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Tsunamis can produce catastrophic damage on vulnerable coastlines, essentially following major earthquakes, landslides or atmospheric disturbances. After the disastrous tsunamis in 2004 and 2011, tsunami science has grown significantly, opening new fields of research for various domains, and also in regions where the tsunami hazard was previously underestimated.
Numerical modeling, complemented with laboratory experiments, are essential to quantify the tsunami hazard. To this end, it is essential to rely on complete databases of past tsunami observations, including both historical events and results of paleotsunami investigations. Furthermore, a robust hazard analysis has to take into account uncertainties and probabilities with the more advanced approaches such as PTHA.
Because the vulnerability of populations, of infrastructures and of the built environment in coastal zones increases, integrated plans for tsunami risk prevention and mitigation should be encouraged in any exposed coastline, consistent with the procedures now in place in a growing number of Tsunami Warning System.

The tsunami session welcomes multidisciplinary contributions covering any of the aspects mentioned here, encompassing field data, regional hazard studies, observation databases, numerical modeling, risk studies, real time networks, operational tools and procedures towards a most efficient warning.

A focus on recent tsunami events all over the globe is encouraged, as well as on the achievements of recent research and operational projects.

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Co-organized by OS2/SM2
Convener: Helene Hebert | Co-conveners: Alberto Armigliato, Miquel Canals, Ira Didenkulova
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| Wed, 06 May, 14:00–18:00 (CEST)

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Session materials Download all presentations (324MB)

Chat time: Wednesday, 6 May 2020, 14:00–15:45

Chairperson: Helene Hebert
D1874 |
EGU2020-7860
| Highlight
Jihwan Kim and Rachid Omira

In the NE Atlantic Ocean, the tsunami hazard is mainly associated to large earthquakes occurring along the Azores-Gibraltar plate boundary, to submarine landslides, or even to the flank collapses in the volcanic Islands. The hazard posed by meteotsunami remains less understood in the region. Yet, the Atlantic coasts of Portugal, Spain and France have experienced at least two meteotsunamis on July 2010 and June 2011. On July 6th and 7th 2010, uncommon sea waves were observed along the coast of Portugal. The Portuguese tide-gauge network recorded the sea-level signals showing tsunami-like waves of heights varying from 0.14 to 0.6 m (crest-to-trough) and of periods in the range of 30 to 60 min. Analysis of both oceanic and atmospheric data
revealed the occurrence of a meteotsunami on the night of July 6th that propagated from Lagos, south, up to Viana de Castelo, north. Here, we present the first investigation of the 2010 meteotsunami that struck the coast of Portugal. We use the atmospheric pressure data to force the sea surface and numerically generate the 2010 meteotsunami. We then simulate the 2010 meteotsunami propagation over high resolution bathymetric models using a validated NLSW code. The comparison of the simulated waveforms with the records shows satisfactory agreement of wave heights and periods in most stations. Taking the 2010 event as a reference of meteotsunamis along the Portuguese coast, we provide an insight on the meteotsunami hazard posed by
events propagating from south to north of the country. This is done by considering a 2D Gaussian shape pressure disturbance that propagates along shelf under varying conditions of speed and incident angle. This allows identifying a number of “hot spots” on the coast of Portugal where the focus of meteotsunami energy is favorable. Our results suggest that meteotsunamis present a real threat on the highly occupied Portuguesecoast and therefore should be considered in tsunami hazard and forecasting strategies of the NE Atlantic countries. This work was supported by the FCT funded project FAST- Development of new forecast skills for meteotsunamis on the Iberian shelf (PTDC/CTA-MET/32004/2017).

D1875 |
EGU2020-771
| Highlight
Alexander Rabinovich, Jadranka Šepić, and Richard Thomson

Meteorological tsunamis are frequently destructive tsunami-like waves generated by small-scale atmospheric disturbances. Several devastating events occurred recently in various regions of the world oceans, including the Balearic Islands, Sicily, the Adriatic and Black seas, the Great Lakes, the west coast of South Korea, the Netherlands and the Persian Gulf. Although this phenomenon has been actively studied for more than 25 years, the exact mechanism (or mechanisms) responsible for producing these extreme events remains a puzzle. One of the major problems making it difficult to determine the physical process generating meteotsunamis is the absence of a network of simultaneously working precise tide gauges and microbarographs in the affected region. A unique set of high-resolution atmospheric data from the meteorological “school network” of 132 school stations became available for 2008-2019 for the area of southern Vancouver Island and nearby Gulf Islands located in the Strait of Georgia. These data, combined with 1-min sea level data from Canadian Hydrographic Service (CHS) and USA National Oceanic and Atmospheric Administration (NOAA) tide gauges, has enabled us to examine both the spatial and temporal features of mesoscale atmospheric disturbances and coincident properties of the associated sea level oscillations. The data analyses, supported by a series of numerical experiments, has made it possible to reconstruct observed events and to determine the specific atmospheric parameters producing the strongest sea level response in the southern part of the Strait of Georgia. These experiments have helped us to recognize the most effective (and hence, most hazardous) directions and speeds of propagating atmospheric disturbances and to identify “hot spots” along the coast that are under the highest risk of large meteotsunamis.

D1876 |
EGU2020-11009
Ryan Mulligan, Alessandro Franci, Miguel Celigueta, and W. Andy Take

Tsunamis generated by highly mobile slides in large-scale flume experiments are simulated with a numerical model called the Particle Finite Element Method (PFEM). The numerical technique combines a Lagrangian finite element solution with an efficient remeshing algorithm, and is capable of accurately tracking the evolving fluid free-surface and velocity distribution in highly unsteady flows. The slide material is water, which represents an avalanche or debris flow with high mobility, and the reservoir depth is varied, thereby achieving a range of different near-field wave conditions from breaking waves to near-solitary waves. Experimental observations of fluid velocity and water surface levels are obtained using high-speed digital cameras, acoustic sensors and capacitance wave probes, and the data are used to analyze the accuracy of the PFEM predictions. The numerical model shows the capability of holistically reproducing the entire problem from landslide motion, to impact with water, to wave generation and propagation. Very good agreement with the experimental observations are obtained, in terms of landslide velocity and thickness, wave time series, maximum wave amplitude, wave speed and wave shape. The results demonstrate the potential of this numerical method for simulating mass flows, impacts with water, and the tsunamis generation process.

D1877 |
EGU2020-9531
Frederic M. Evers and Robert M. Boes

Landslide tsunamis generated by extremely rapid subaerial mass wasting are also referred to as impulse waves and may occur both along coastal areas and in inland waters including engineered reservoirs. The hydraulic process chain comprising wave generation, propagation, and run-up needs to be comprehensively assessed to predict whether these waves represent a threat to the shore and adjacent infrastructure. Hazard assessment studies based on site-specific hydraulic laboratory models and numerical simulations may generally yield quite accurate predictions of the expected wave and run-up heights. While the former involves the availability of specialized lab infrastructure and instrumentation, the latter requires in-depth knowledge of suitable numerical methods as well as experience in their application to scenarios at prototype-scale. Therefore, both approaches are time-consuming, involve high costs, and pose substantial entry thresholds for practitioners. Especially in emergency situations, when first-order estimations need to be quickly at hand, the ad-hoc applicability of these approaches may therefore be limited.

Motivated by an imminent landslide hazard at Carmena reservoir, Switzerland, in 2002, the national supervisory authority for dam safety, the Swiss Federal Office of Energy, commissioned the development of a fast and readily applicable computational procedure. As a result, the first edition of the so-called ‘impulse wave manual’ was published in 2009 and provides an extensive literature review of generally applicable equations derived from lab experiments. It combines selected equations into a coherent computational framework covering all stages of an impulse wave event’s hydraulic process chain. Based on the estimation of e.g. wave and run-up heights, this manual allows to rapidly implement mitigation measures including reservoir drawdown or precautionary evacuation. In addition to an improved emergency planning, the manual proved to be an inexpensive tool to obtain an estimation of an impulse wave event’s magnitude during the preliminary design phase of new reservoirs. Back in 2009, the manual’s literature analysis already identified specific research gaps, leading to the initiation of further experimental investigations. Following these research efforts over the past ten years, a second edition of the manual was published in 2019 featuring an updated computational procedure.

This contribution provides a brief introduction to the updated computational procedure and applies it to prototype events with available survey data, e.g. Chehalis Lake, Canada, in 2007. The comparison to prototype data allows to highlight the procedure’s capabilities as well as its limitations for future ad-hoc estimations of landslide-generated impulse waves.

D1878 |
EGU2020-11838
| Highlight
Hermann M. Fritz, Tubagus Solihuddin, Costas E. Synolakis, Gegar S. Prasetya, Jose C. Borrero, Vassilis Skanavis, Semeidi Husrin, Widjo Kongko, Dinar C. Istiyanto, August Daulat, Dini Purbani, Hadiwijaya Salim, Rahman Hidayat, Velly Asvaliantina, Maria Usman, and Ardito Kodijat

On December 22, 2018, an eruption and partial collapse of the Anak Krakatau volcano generated a tsunami in the Sunda Strait. The tsunami caused catastrophic damage and more than 400 deaths in coastal regions of the Sunda Strait in Lampung (Sumatra) and Banten (Java). An international tsunami survey team (ITST) was deployed 6 weeks after the event to document flow depths, runup heights, inundation distances, sediment deposition, impact on the natural environment and infrastructure. The 4 to 9 February 2019 ITST focused on islands in the Sunda Strait: Rakata, Panjang, Sertung, Sebesi and Panaitan. The survey team logged more than 500 km by small boat. The collected survey data includes almost 100 tsunami runup and flow depth measurements. The tsunami impact peaked along steep slopes facing Anak Krakatau with an 85 m runup on Rakata and an 83 m runup on Sertung. The extreme runup heights were within less than 5 km of Anak Krakatau. Flow depth reached more than 11 m above ground on Sertung where a boat landing was possible and trees remained standing. On Sebesi Island located 15 km northeast of the source tsunami runup heights remained below 10 m. In contrast, tsunami heights exceeding 10 m were observed in the Ujung Kulon National Park located 50 km southwest of Anak Krakatau. The runup distributions on the islands encircling Anak Krakatau highlight the directivity of the tsunami source with the Anak Krakatau collapse towards the southwest. Inundation and damage were mostly limited to within 400 m of the shoreline given the relatively short wavelengths of volcanic tsunamis. Significant variation in tsunami impact was observed along shorelines of the Sunda Strait with tsunami heights rapidly decreasing with distance from the point source. Field observations, drone videos, and satellite imagery are presented. The team interviewed numerous eyewitnesses based on established protocol and educated residents about tsunami hazards. The tsunami caught the locals off guard despite the history and a six-month long eruptive activity in the lead up. Community-based education and awareness programs are essential to save lives in locales at risk from locally generated tsunamis. The 500 m initial height difference between the 1883 Krakatau and 2018 Anak Krakatau collapses provides a perspective on these two tsunamis. Remaining and future tsunami hazards will be affected by volcanic edifice regrowth.

D1879 |
EGU2020-13314
| Highlight
Mohammad Heidarzadeh, Purna Sulastya Putra, Abdul Muhari, and Septriono Hari Nugroho

We report results of field surveys and numerical modeling of the tsunami generated by the Anak Krakatau volcano eruption on 22 December 2018. We conducted two sets of field surveys of the coastal areas destroyed by the Anak Krakatau tsunami in 26-30 December 2018 and 4-10 January 2020. Field surveys provided information about the maximum tsunami height as well as the most damaged area. The maximum tsunami height was up to 13 m. Most locations registered a wave height of 3-4 m. Tsunami inundation was limited to approximately 100 m. For modeling, we considered 12 source models and conducted numerical modeling. The scenarios have source dimensions of 1.5–4 km and initial tsunami amplitudes of 10–200 m. By comparing observed and simulated waveforms, we constrained the tsunami source dimension and initial amplitude in the ranges of 1.5–2.5 km and 100–150 m, respectively. The best source model involves potential energy of 7.14 × 1013–1.05 × 1014 J which is equivalent to an earthquake of magnitude 6.0–6.1.

D1880 |
EGU2020-21558
| Highlight
Thomas Zengaffinen, Finn Løvholt, and Geir Pedersen

The 2018 Anak Krakatoa volcano flank collapse and tsunami caused several hundred fatalities. There was no early warning system in place for the landslide triggered tsunami, and there is a lack in understanding on how the failure mechanism affected landslide dynamics and tsunami generation, which we focus on in this study. While researchers previously have modelled the collapse as an instantaneous release, we here illuminate how different landslide failure scenarios, including a gradually released flank failure, influence the tsunami generation. We simulate the material movement by using a viscoplastic flow model with Herschel-Bulkley rheology and we employ a depth-averaged model to both the landslide and the tsunami propagation. A sensitivity study to the gradual mass release, total release volume, the material yield strength, the remoulding coefficient, and landslide directivity is used to shed light on the tsunami generation. Our analysis indicates that an instantaneous mass release in 125 degree SW direction fits the observed waveforms at coastal gauge stations best. In our simulations, we observe, as many other authors, discrepancies between simulated and observed arrival times and wave periods offshore Sumatra. Hence, we have also investigated sensitivity to the bathymetric depth by varying the water depth in areas near the source. Finally, we simulate the tsunami inundation at two coastal sites in southwestern Java using open-source topographic data. Given the limitations in the topographic data, a reasonably good agreement between the simulations and observations are obtained.

D1881 |
EGU2020-436
Cristina Sanchez Serra, Eulàlia Gràcia Mont, Roger Urgeles Esclasans, Sara Martínez-Loriente, Rafael Bartolome, Manuela Volpe, Francesco Maesano, Roberto Basili, Fabrizio Romano, Antonio Scala, and Laura Gómez de la Peña

The Lineament South (LS) is a major WNW-ESE trending dextral strike-slip fault located along all the Gulf of Cadiz (SW Iberian margin), and it has been considered as the plate boundary between Africa and Eurasia. The SW Iberian margin hosts a moderate to intermediate seismic activity, however, largest and destructive earthquakes and tsunamis have occurred in this area, such as the 1st of November 1755 Lisbon earthquake and tsunami (Mw ≥ 8.5) and the 28th February 1969 earthquake (Mw 7.8). Our work focus on the LS active structure and their potential seismic and tsunami hazard. To study the LS, we integrated the most advanced technologies in marine geosciences covering different scales of resolution, such as: a) Multibeam echosounder that allows us to obtain a bathymetric map that provides information of the seafloor; b) Sub-bottom profiler to acquire high-resolution seismic profiles of the uppermost layers below seafloor; c) Autonomous Underwater Vehicle (AUV) “Abyss” to carry out a micro-bathymetric survey (2 m resolution); and d) High-resolution 2D multichannel seismic profiles. With these dataset, we characterized the LS structure and their sub-surface, calculated the maximum magnitude earthquake and modelled the worst-case tsunami scenario that this fault may produce. The workflow to develop the tsunami modelling involves the following tasks: 1) Interpretation of the high-resolution seismic profiles; 2) Map the trace of the LS fault; 3) Generate a seismo-stratigraphic model of the fault subsurface; 4) Define the specific attributes and seismic/tsunamigenic parameters of the LS fault system; 5) Determine the maximum magnitude and slip according to Leonard (2014) scaling-laws; and 6) Run the tsunami simulation using the Tsunami-HySEA software. The LS extends for more than 370 km, from the Horseshoe Abyssal Plain to the Gulf of Cadiz Imbricated Wedge, as demonstrated for the sequence of MCS profiles across the lineament. In the AUV map, we can recognize fault traces, which are not continuous and show a set of crests and troughs of a width of 100s of meters. The deformation associated to LS span’s about 2-3 km at the seafloor cutting the seismo-stratigraphic sequences, including the Quaternary unit, which reach up to the seafloor. According to the scaling-law of Leonard (2014), the maximum magnitude earthquake that LS can generate is up to Mw 7.9. An earthquake of this magnitude can produce a tsunami that may affect the SW Iberian Peninsula, with a wave amplitude higher than 1 m. Eventually, the LS may generate a significant earthquake and tsunami along the Portuguese, Spanish and Moroccan coasts.

D1882 |
EGU2020-3972
Emile Okal and Costas Synolakis

The classic approach to tsunami simulation by earthquake sources consists
of computing the vertical static deformation of the ocean bottom due to
the dislocation, using formalisms such as Mansinha and Smylie's [1971] or
Okada's [1985], and of transposing that field directly to the ocean's
surface as the initial condition of the numerical simulation.
We look into the limitations of this approach by developing a very
simple general formula for the energy of a tsunami, expressed as the
work performed against the hydrostatic pressure at the bottom of
the ocean, in excess of the simple increase in potential energy
of the displaced water, due to the irreversibility of the process.
We successfully test our results against the exact analytical solution
obtained by Hammack [1972] for the amplitude of a tsunami generated
by the exponentially-decaying uplift of a circular plug on the ocean
bottom. We define a "tsunami efficiency" by scaling the resulting energy
to its classical value derived, e.g., by Kajiura [1963]. As expected, we
find that sources with shorter rise times are more efficient tsunami
generators; however, an important new result is that the efficiency is
asymptotically limited, for fast sources, to a value depending on the
radius of the source, scaled to the depth of the water column; as this
ratio increases, it becomes more difficult to flush the water out of
the source area during the generation process, resulting in greater
tsunami efficiency. Fortunately, this result should not affect
significantly the generation of tusnamis by mega-earthquakes.

D1883 |
EGU2020-3152
Raissa Mazova, Leopold Lobkovsky, Jorge Van Den Bosch F, Natalya Baranova, and Gustavo Oses A

Numerical modeling of the generation and propagation of tsunami waves during the earthquake of 1877 in Chile was performed. The possible dynamics of the seismic source are estimated, the wave characteristics of the process and the distribution of the maximum tsunami wave heights along the coast of the considered water area are obtained. On May 9, 1877, at 9:16 pm local time, an earthquake and subsequent tsunami were recorded in the area of ​​Iquique. The epicenter of the earthquake was in the Pacific Ocean near the city of Iquique. The calculated magnitude of the earthquake was estimated at 8.5-8.8. The highest intensity was noted between the cities of Arica, Iquique and Antofagasta, Tokopiglia, Gatiko and Kobikha were also severely affected. All these cities were destroyed. Earthquake victims were reported from Pisco to Antofagasta. In the area of ​​the cities of Iquique, Gatico and Kobiha, five minutes after the earthquake, tsunami waves arrived with a first wave height of 10 to 15 meters. The second wave she came in 15 minutes after the main shock, she was more powerful - her height was from 20 to 23 meters. It should be noted that in various documentary sources the data for a number of points on the Chilean coast are contradictory. So, for example, in Arica the spread of wave heights from 9 to 20m, in Iquique 6-9m, in Kobikha 9-12m, in Mejilones a spread from 12 to 21m. Given the very diverse information on the tsunami wave height on the coast and based on the conclusions of the authors of [1] on the similarity of the continental slope of the deep sea trench near Arica city and Kuril-Kamchatka area, for which the earthquake key model was successfully applied in [2] [3], we suggested that the 1877 earthquake had complex dynamics. For the numerical implementation of this process, it was decided to use the key model of the earthquake, which allows breaking the earthquake source into a large number of block keys, taking into account aftershock activity and bathymetry of the earthquake source area. In this process, the displacement of each block in the source of the earthquake occurs by a different amount at different times. When numerically simulating an earthquake and generating tsunami waves, the key model of the earthquake source allows you to obtain a complex distribution of the maximum wave heights on the shore, for a given dynamics of blocks in the earthquake source.

 

[1] Mazova R.Kh,  Ramirez J.F. Tsunami waves with an initial negative wave on the Chilean coast // Natural Hazards 20 (1999) 83-92. 

[2] Lobkovsky, L. I., Mazova, R. Kh, Kataeva, L Yu., & Baranov, B.V.  Generation and propagation of catastrophic tsunami in the basin of Sea of Okhotsk. Possible scenarios, // Doklady, 410, 528–531 (2006).

[3] Lobkovsky L.I., Baranov BV. Keyboard model of strong earthquakes in island arcs and active continental margins // Doklady of the Academy of Sciences of the USSR. V. 275. № 4. P. 843-847. 1984.

D1884 |
EGU2020-10927
Viacheslav Karpov, Sergey Kolesov, Mikhail Nosov, Anna Bolshakova, Gulnaz Nurislamova, and Kirill Sementsov

In this talk the fully automatic system for estimate of tsunamigenicity of an earthquake is presented. The system is focused on simplicity and speed with usage of minimum of input data. The input dataset for the system includes (1) earthquake coordinates, (2) earthquake depth, (3) seismic moment, (4) focal mechanism. We use datasets provided by USGS and GEOFON. Upon receiving earthquake data the system performs the following consecutive actions. At first, the vector field of co-seismic bottom deformation is obtained using earthquake fault parameters and empirical relationships. Then the initial elevation in tsunami source is calculated and estimation of Soloviev-Imamura tsunami intensity is performed. Initial elevation is calculated taking into account vertical and horizontal components of bottom deformation, local bathymetry (GEBCO) and smoothing effect of water layer. An auxiliary study was conducted to obtain relationship between potential energy of initial elevation of water in tsunami source and intensity of resulting tsunami. More than 200 historical events from HTDB/WLD and NGDC/WDS databases was statistically processed. The obtained relationship is used to assess the intensity of tsunami generated by earthquake under consideration. Finally, if event is considered significant (energy > 109 J), the numerical simulation of propagation of tsunami waves is performed. As a result of numerical simulation, animations of wave propagation, distribution of maximum tsunami heights, and water surface time-histories in a number of given points are produced. Details of implementation, physical constraints, future development of system as well as 2-years experience of the system operation will be discussed during the talk.

Acknowledgements

This work was supported by the Russian Foundation for Basic Research, projects 20-07-01098, 20-35-70038, 19-05-00351.

D1885 |
EGU2020-19848
Jorge Macias, Manuel J. Castro, Marc de la Asunción, José Manuel González-Vida, Carlos Sánchez-Linares, Finn Lovholt, and Stefano Lorito

Tsunami simulation in the framework of Tsunami Early Warning Systems (TEWS) is a quite recent achievement, but still limited regarding the size of the problem and restricted to tsunami wave propagation. Faster Than Real Time (FTRT) tsunami simulations require greatly improved and highly efficient computational methods to achieve extremely fast and effective calculations. HPC facilities have the role to bring this efficiency to a maximum possible and drastically reducing computational times. Putting these two ingredients together is the aim of Pilot Demonstrator 2 (PD2) in ChEESE project. This PD will comprise both earthquake and landslide sources. Earthquake tsunami generation is to an extent simpler than landslide tsunami generation, as landslide generated tsunamis depend on the landslide dynamics which necessitate coupling dynamic landslide simulation models to the tsunami propagation. In both cases, FTRT simulations in several contexts and configurations will be the final aim of this pilot.

Among the objectives of our work in ChEESE project are achieving unprecedented FTRT tsunami computations with existing models and investigate the scalability limits of such models; increasing the size of the problems by increasing spatial resolution and/or producing longer simulations while still computing FTRT, dealing with problems and resolutions never done before; developing a TEWS including inundation for a particular target coastal zone, or numerous scenarios allowing PTHA (PD7) and PTF (PD8), an aim unattainable at present or including more physics in shallow water models for taking into account dispersive effects.

Up to now, the two European tsunami flagship codes selected by ChESEE project (Tsunami-HySEA and Landslide-HySEA) have been audit and efficiency further improved. The improved code versions have been tested in three European 0-Tier HPC facilities: BSC (Spain), CINECA (Italy) and Piz Daint (Switzerland) using up to 32 NVIDIA Graphic Cards (P100 and V100) for scaling purposes. Computing times have been drastically reduced and a PTF study composed by around 10,000 scenarios (4 nested grids, 12 M cells, 8 hours simulations) have been computed in 6 days of wall-clock computations in the 64 GPUs available for us at the BSC.

 Acknowledgements. This research has been partially supported by the Spanish Government Research project MEGAFLOW (RTI2018-096064-B-C21), Universidad de Málaga, Campus de Excelencia Internacional Andalucía Tech and ChEESE project (EU Horizon 2020, grant agreement Nº 823844), https://cheese-coe.eu/

D1886 |
EGU2020-4675
Yuichiro Tanioka, Mayu Inoue, and Yusuke Yamanaka

A dense cabled observation network, called the seafloor observation network for earthquakes and tsunami along the Japan Trench (S-net), was installed in Japan. This study aimed to develop a near-real time tsunami source estimation technique using a simple classification of waveforms observed at the ocean bottom pressure sensors in S-net. To investigate the technique, synthetic pressure waveforms at those sensors were computed for 64 tsunami scenarios of large earthquakes with magnitude ranging between M8.0 and M8.8. The pressure waveforms within a time window of 500 s after an earthquake were classified into three types. Type 1 has the following pressure waveform characteristic: the pressure decreases and remains low; sensors exhibiting waveforms associated with Type 1 are located inside a co-seismic uplift area. The pressure waveform characteristic of Type 2 is that one up-pulse of a wave is within the time window; sensors exhibiting waveforms associated with Type 2 are located at the edge of the co-seismic uplift area. The other pressure waveforms are classified as Type 3.

Subsequently, we developed a method to estimate the uplift area using those three classifications of pressure waveforms at sensors in S-net and a method to estimate earthquake magnitude from the estimated uplift area using a regression line. We systematically applied those methods for two cases of previous large earthquakes: the 1952 Tokachi-oki earthquake (Mw8.2) and the 1968 Tokachi-oki earthquake (Mw8.1). The locations of the large computed uplift areas of the earthquakes were well defined by the estimated ones. The estimated magnitudes of the 1952 and 1968 Tokachi-oki earthquakes from the estimated uplift area were 8.2 and 7.9, respectively; they are consistent with the moment magnitudes derived from the source models. Those results indicate that the tsunami source estimation method developed in this study can be used for near-real time tsunami forecasts.

This method is so simple that we do not need any numerical tsunami simulation or other sophisticated techniques but only need the classification of observed pressure data into three types.

D1887 |
EGU2020-11411
Aditya Gusman, Anne Sheehan, and Kenji Satake

Tsunami warnings in New Zealand rely on first locating and determining size of a large earthquake and then using precomputed simulation results to forecast the threat level and timing of the resulting tsunami. The number of offshore pressure gauges for tsunami monitoring around the world is increasing and it provides the opportunity to develope new methods to forecast tsunamis. In cases where a dense array of offshore pressure gauges is available, a data assimilation method can be applied to estimate the tsunami using the observations of pressure changes. Here we apply the data assimilation method to the tsunami generated from the 2009 Dusky Sound, New Zealand, magnitude 7.8 earthquake and determine a rapid and accurate estimate of the tsunami wave arrival time and size along the west coast of New Zealand.  The tsunami was recorded by the Marine Observations of Anisotropy near Aotearoa (MOANA) OBS network which consists of a total of 30 differential pressure gauges.

We use tsunami waveform inversion applied to Deep‐ocean Assessment and Reporting of Tsunamis (DART) offshore pressure gauge and coastal tide gauge data to estimate the fault slip distribution of the Dusky Sound earthquake. The tsunami from this fault slip estimate is then used as a reference to measure the forecast accuracy from different methods to forecast the tsunami threat in New Zealand’s tsunami warning zones. Methods that are evaluated here include the currently operational tsunami warning procedure in New Zealand, tsunami data assimilation that relies only on the dense pressure gauge array data, and tsunami data assimilation with an initial condition model from W-Phase inversion result.

A good match was found between the forecast from the data assimilation method and observed tsunami waveforms at the Charleston tide gauge station on the west coast of New Zealand's South Island. However, this method gives an accurate forecast only along the west coast of New Zealand because the offshore pressure gauge network is located off the west coast of the South Island. While an advantage of the data assimilation is that no initial condition is needed, we find that our forecast is improved especially along the south and east coasts of the South Island by merging tsunami forward modelling from a rapid W‐phase earthquake source solution with the data assimilation method.

D1888 |
EGU2020-4349
| Highlight
Ian Robertson

ABSTRACT:

Virtually every tsunami that has affected coastal communities in the past few decades has resulted in loss of life, often in the tens of thousands or more. Increased population density along tsunami-prone coastlines will only increase the potential for loss of life during future tsunamis. Conventional evacuation planning focuses on early warning systems and horizontal evacuation to the nearest available high ground. While  this approach should be encouraged and improved, there is also a need for vertical evacuation options for areas where horizontal evacuation is not possible, or where residents, for whatever reason, are still in the inundation zone when the tsunami waves arrive.

Vertical evacuation into sturdy buildings that are tall enough to provide refuge areas above the inundation elevation has saved innumerable lives during past tsunamis. Most of these buildings were never designed for tsunami loads, but nevertheless remained intact and protected those who sought refuge in the upper floors.  Seismic design requirements are common in tsunami-prone areas, which increases a building’s potential to survive the tsunami loads.  However, consciously designing for tsunamis would increase the reliability of vertical evacuation significantly.

The 2016 edition of “ASCE 7 – Minimum Design Loads and Associated Criteria for Buildings and Other Structures” includes a new Chapter 6 on Tsunami Loads and Effects. This chapter provides a comprehensive approach to probabilistic tsunami design of buildings and other structures for various performance levels. One section of this chapter provides specific requirements for design of vertical evacuation refuge structures for tsunamis, which results in less than 1% probability of failure during a design level tsunami. It is also strongly recommended that all buildings in the tsunami inundation zone that are tall enough to provide safe refuge should include tsunami design, even if at a less stringent level of performance.

This presentation will discuss the implications of adding tsunami design, evaluate the cost premium involved, and present some recent VERT design and construction projects.

D1889 |
EGU2020-3815
Hiroshi Kitazato, Yuri Oki, and Soichiro Yasukawa

Coastal land- and sea-scapes are composed of diverse habitats such as reed bed, salt marsh, tidal-flats, sea grass fields, seaweed grounds, sandy and rocky-shores. Coastal habitats harbor both biodiversity and abundance of coastal lives. These complex coastal ecosystems are sustained by the function of land-sea linked material cycles. Coastal ecosystems provide wide ranges of ecosystem services and processes among natural environments, fisheries, and human livelihoods.  Protecting coastal ecosystems secure material cycle, which is fundamental for sustainable human livelihood in coastal communities prone to disasters. In addition, bio-diverse coastal species such as sea grasses, function as nursery areas for commercially important seafood species such as fishes, clams, shrimps, and others. On the other side, coastal ecosystems provide natural infrastructure for both prevention and reduction from hazardous events, known as ecosystem-based disaster risk reduction (eco-DRR).  For establishing concept of eco-DRR, we need to prepare precise coastal biological, geological and other data including human and social activities.  Habitat map projection is effective way to pile multi-disciplinary data on same GIS grid.  Habitat map, thus, provides common data sets to multiple stakeholders, such as scientists, fishermen, local fish markets and local and federal governments for planning coastal management systems.

    Earthquakes and Tsunamis should give heavy damages on coastal lives and ecosystems in global scale.  Because, more than half of world populations concentrate into vulnerable coastal areas.  Together with the conventional hard-infrastructure measures, we have witnessed in previous disasters, that eco-DRR is both affordable and sustainable solution.  Eco-DRR should be further promoted, not only in the preparedness and mitigation, but also for the better reconstruction from the disasters so to "Build Back Better". We plan to show a couple of best practices in terms of Eco-DRR activities from March 11, 2011 Earthquake and Tsunamis.

D1890 |
EGU2020-4033
Yo Fukutani

For a probabilistic tsunami risk assessment of multiple sites, it is important to consider the spatial correlation between tsunami inundation depth and the sites because it affects the aggregated probability distribution of site damages. Various uncertainties such as ground motion, building response characteristics, and material strength are considered in the probabilistic seismic risk assessment. However, any research that evaluates the spatial correlation characteristics of tsunamis is yet to be reported. In this study, we evaluate the macro spatial correlation coefficient of the tsunami inundation depth according to the relative distance in the tsunami run-up region. We firstly constructed the fault parameters of the Sagami trough earthquake which has a large slip off the Kanto area in Japan. The moment magnitude of the earthquake is 8.7, and there are 6,149 small faults. Using the initial water level calculated from the earthquake parameters as input data, we solved the continuous equation and 2D linear long wave equation, targeting Zushi city, Kanagawa Prefecture. The maximum tsunami inundation depth was 8.71 m. We regressed the exponential function (ρ(x) = aexp(bx) + cexp(dx)) for the relationship between the distance from the coastline and the tsunami inundation depth. As a result, we obtained an evaluation formula with a relatively high accuracy. The coefficient were a = 0.4555, b = −0.1653, c = 0.5434, d = −0.007345 and the determination coefficient was 0.992. The results of this study can be used for a probabilistic tsunami risk assessment for multiple sites.

D1891 |
EGU2020-5554
Viviane Souty and Audrey Gailler

Probabilistic Tsunami Hazard Assessment (PTHA) is a fundamental tool for producing time-independent forecasts of tsunami hazards at the coast using data from tsunami generated by local, regional and distant earthquake source. If high resolution bathymetry and topography data at the shoreline are available, local tsunami inundation models can be developed to identify the highest risk areas and derive evidence-based evacuation plans to improve community safety.
This study takes part of the H2020-Euratom NARSIS project (2017-2021), which aims at making significant scientific updates of some elements required for the Probabilistic Safety Assessment, focusing on external natural events (earthquake, tsunami, flooding, high speed winds...). In this framework, we are developing a PTHA approach to estimate the tsunami hazard along the French Mediterranean coasts at a local level. The probability of occurrence of tsunamigenic earthquakes is the foundation of our work as wrong probabilities would lead to a wrong evaluation of the tsunami hazard. We first discuss the various uncertainties from the determination of the tsunami sources to the simulation of the propagation of the tsunami to the coast. We then present the results of tsunami hazard in the city of Cannes (French Riviera).

D1892 |
EGU2020-3227
Yan Xiong, Qiuhua Liang, Gang Wang, and Yunsong Cui

Extreme natural hazards such as tsunamis or storm surges have been frequently reported in recent years, posting serious threat to people and their properties. Numerical modelling has provided an indispensable tool to predict these hazardous events and assess their risks. However, most of the current models are based on the assumption of “clean” water and neglect the impact of floating debris as observed in reality. The interactive processes between the floating debris and the background fluid flow have not been well explored and understood. Few reliable modelling tool has been reported for simulating and predicting these complicated processes.

This work presents a two-way dynamic method to couple a 2D shallow flow hydrodynamic model with a discrete element method (DEM) model for simulating and analyzing the interactive process between fluid flow and floating debris under the extreme hydraulic conditions induced by tsunami or flash flooding. The proposed two-way coupling approach uses the high-resolution water depth and velocity predicted by the hydrodynamic model to quantify the hydrostatic and dynamic forces acting on the floating objects; the corresponding counter forces on the fluid are subsequently taken into account by including extra source terms in the governing shallow water equations (SWEs) of hydrodynamic model. This new approach lifts the limitation of traditional approaches that reply on calibrated empirical parameters to quantify the forces. In developing the resulting coupled model, a multi-sphere method (MSM) is adopted and implemented in the DEM model to simulate solid debris. This method ensures that the interaction of fluid and solid is realistically modelled and the application is not restricted by shapes and sizes of debris.

The new coupling model is validated against a dam-break flume experiment with three floating objects impacting two fixed obstacles. The predicted results in terms of water depth and floating object displacements in both horizontal and vertical directions compare well with the experimental observations. Furthermore, the new coupled model is computationally accelerated by implementation on modern GPUs to achieve high-performance computing. It provides a robust and innovative modelling tool for the simulation of large-scale flooding process including debris impact and assess the resulting risk.

D1893 |
EGU2020-12410
Marine Le Gal and Satoshi Mitarai

In 1771, a major tsunami event hit the Yaeyama Islands (Japan) and particularly Ishigaki Island, where 30m run-ups were estimated. As with many other Pacific Islands, Ishigaki Island is surrounded by a reef. Interactions between tsunami waves and reefs have generally been analyzed with idealized models and studies focusing on a specific reef are rare. It has been shown that the influence of the reef is two-fold : it can either amplify or buffer waves. For the particular 1771 event, this influence is still unknown and the present study aims to identify it. Several numerical models were developed using the 2D Nonlinear Shallow Water model of the Telemac system. First, a reference model was build, simulating the real event with an accurate reef representation. Then, altered bathymetry models were generated and compared to the reference model. In our simulations, overall, the reef protected the coast with a 12,5% decrease of the water depth at the shoreline. However channels, disrupting the continuity of the reef, strongly amplified inundations on the nearby coast, with up to 40% increase of the water depth at the shoreline. To go further, this results could provide inside to better manage the coast for future events.

D1894 |
EGU2020-7542
Ivana Bosnic and Pedro Costa

Understanding past tsunami events is key to assess tsunami hazard and numerical modelling is a powerful tool to better understand these events. A rising number of studies focusing on palaeotsunami numerical modelling reinforce the potential of this tool to unravel unknown features of past tsunami events. The AD 1755 Lisbon is the largest historical tsunami registered on Western Europe and despite its relevance there are still uncertainties regarding its source, magnitude and wave characteristics.   

This work contributes to a better understanding of the AD 1755 tsunami through the evaluation of the wave characteristics and of the onshore and offshore sedimentary dynamic using Delft3D software (Flow module).  

The study site, Almargem lowland, is located on the Portuguese southern coast (central Algarve) where a two-dimensional vertical (2DV) morphodynamic modelling approach was carried out along 10 vertical layers. Bathymetry is represented by a across-shelf profile with 7 kilometers long thus, extending from the coast up to 50 m deep. Bottom sediments and roughness vary along the profile according to the sediment characteristics of each coastal sector (shelf, beach, dune and lowland area). Boundary conditions were imposed according to three scenarios represented by offshore sinusoidal tsunami waves of 3, 4- and 5-meters height. Tsunami-induced sedimentary dynamics results show that the 3 m wave scenario (50 m depth) present the most compatible scenario with the observed onshore deposit, in particular its 600 m inland extension. Moreover, the dune was singled-out as the main sediment source of the deposit. This source-to-sink relationship confirms previous field and sedimentary results (Costa et al., 2012, Sed Geol).  

A 3D morphodynamic modelling approach carried out by Dourado et al. (in press) on an adjacent study area (Salgados, central Algarve) also pointed to a 3-meter tsunami wave height (at 50 meters deep) and further corroborates the results of this work. Despite good initial results, with harmonization and validation of modelling results, further efforts are necessary to incorporate backwash influence on the onshore sediment dynamics as well as a detailed analysis on the vertical sediment distribution. 

The authors would like to acknowledge the financial support from FCT through projects UIDB/50019/2020 – IDL and PTDC/CTA-GEO/28941/2017 - OnOff. 

D1895 |
EGU2020-9875
| Highlight
Filippo Zaniboni, Gianluca Pagnoni, Glauco Gallotti, Stefano Tinti, and Alberto Armigliato

The recent paroxysmal crisis occurring on the island of Stromboli (Tyrrhenian Sea, Italy), manifesting into two main events during summer 2019 (3rd July and 28th August), renovated the attention on the possibility of tsunami generation induced by volcanic activity. The Stromboli edifice is characterized by the Sciara del Fuoco scar on its north-western flank channeling most of the material ejected from the crater to the sea.

In this area, in December 2002, two landslides (the first submarine, the second subaerial) triggered large waves affecting the whole coast of the island, causing severe damages but fortunately no casualties, due to the non-touristic period. The tsunami rapidly dissipated with distance, being observed in Panarea (20 km south-east of Stromboli), as is typical of non-seismic tsunamigenic sources. A similar occurrence during summer would have resulted into dramatic consequences, especially along the Stromboli coasts.

In this study, the tsunamigenic potential associated with destabilized mass along Stromboli flanks is evaluated by means of numerical, in-house developed, codes with the aim of providing insights on the tsunami hazard along the coasts of Stromboli, of the surrounding Aeolian archipelago and in general in a larger domain covering the southern coasts of Tyrrhenian Sea as well.

D1896 |
EGU2020-11292
Yibin Liu and Hermann M. Fritz

Among the wide spectrum of volcanic tsunamis, the most devastating events have been caused by extremely explosive eruptions, pyroclastic flows and debris avalanches of underwater or near surface volcanos. The 2015 “orange” alert at the Kick ‘em Jenny submarine volcano in the Caribbean Sea highlighted the challenges in characterizing the tsunami waves for a potential submarine volcanic eruption. The 2018 Anak Krakatau eruption and flank collapse generated tsunami resulted in a near water surface setting of the volcanic vents similar to these laboratory experiments and relevant for the remaining and future tsunami hazards.

Source and runup scenarios are physically modeled using generalized Froude similarity in the three dimensional NHERI tsunami wave basin at Oregon State University. A novel volcanic tsunami generator (VTG) was deployed to study submarine volcanic eruptions with varying initial submergence and kinematics. The VTG consists of a telescopic eruptive column with an outer diameter of 1.2 m. The top cap of the pressurized eruptive column is accelerated vertically by eight synchronized 80 mm diameter pneumatic pistons with a stroke of 0.3 m. More than 300 experimental runs have been performed which include around 120 combinations of velocities and water depths. The variable eruption velocities of the VTG can mimic a wide range of processes ranging from relatively slow mud volcanoes and rapid explosive eruptions. The gravitational collapse of the eruptive column represents the potential engulfment and caldera formation. Water surface elevations and onshore runup are recorded by an array of resistance wave gauges and runup gauges. The VTG displacement is measured with an internal linear potentiometer and above and underwater camera recordings. Water surface reconstruction and kinematics are determined with a stereo particle image velocimetry (PIV) system. The water surface spike from the concentric collision of wave crest is observed under a limited range of Froude numbers. The energy conversion rates from the volcanic eruption to the wave train are quantified for various scenarios. Predictive equations of wave and spike characteristics are obtained and compared with existing linear and non-linear theories. The measured volcanic eruption and tsunami data serve to validate and advance three-dimensional numerical volcanic tsunami prediction models.

D1897 |
EGU2020-22056
Moisés Brito, Daniel Conde, José M. Domínguez, and Rui M.L. Ferreira

The tragic tsunami events of Indonesia, the 28th September 2018 Palu Bay landslide and the partial collapse of the Anak Krakatau volcano on the 22nd December 2018, and Greenland, the Karrat Fjord landslide on the 17th June 2017, have brought new attention to slope-failure tsunami genesis. Earlier modelling attempts, based on the Lituya bay tsunami were mostly based on mesh-based solvers of the Navier-Stokes (NS) and incompressible continuity equations. This entailed tracking the interfaces between solid and liquid phases as the granular landslide enters the water.

In this work, we attempt to overcome the limitations of mesh-based models while maintaining affordable the total computational time. For this purpose, we present a methodology to couple the 2D shallow-water solver HiSTAV with the 3D Smooth Particle Hydrodynamics based NS solver DualSPHysics. Recently, DualSPHysics has been coupled with the Chrono-Engine library, developed as general-purpose simulator for three-dimensional multi-body problems with support for very large systems, which benefits from advances the in parallel and distributed computing solutions for fluids and multibody systems. Furthermore, Lagrangian, meshless SPH solvers present many advantages when computing interactions between objects or structures and the flow, naturally dealing with unsteady and nonlinear flows, extreme deformations and complex topological evolutions.

The shallow-water model HiSTAV, developed at CEris, Instituto Superior Técnico, benefits from a computational implementation, featuring a distributed and heterogeneous computing framework for hyperbolic solvers, that makes it particularly suitable to integration with 3D solvers. The mathematical core of HiSTAV is governed by the hyperbolic shallow-water equations, with depth-averaged transport of granular-fluid mixtures, solved by a 1st order explicit and fully conservative method.  Specific changes to the numerical scheme, namely 2nd order discretization and non-hydrostatic pressure terms, are proposed and evaluated regarding the obtained solution quality improvements. The most notable influence of these terms is on breaking wave cases, where 1st order schemes are unable to capture the waveform with an acceptable error.

The proposed modifications, coupled with the computational gains in HiSTAV, aim at providing a fast and robust platform for tsunami modelling at all relevant scales, from source to run-up, in both natural and built environments.

The strategy to couple DualSPHysics and HiSTAV is based on the bi-directional link at the 3D-2D interfaces modified to take into account that the 3D information is not organized in cells or nodes. The solution of the NS equations is integrated in an overlapping region of the domain and provides data that is passed to the 2D domain by the boundary eigenvalues. This strategy is mathematically exact in the absence of complex topography or bottom friction. Boundary conditions for pressure and velocity are then updated at the boundary of the 3D model for the next relevant SPH time step. Computational gains are attained by the fact that the 2D simulations are run in accordance with the 2D CFL condition and thus not at all 3D time steps.

The method is applied to the problem of forecasting the impacts of a landslide induced tsunami in the Tagus estuary.

D1898 |
EGU2020-18230
Zhenzhu Meng, Christophe Ancey, and Ivan Maeder

Tsunami generated by landslides is one of the major threats to populations in coastal areas. A recent example is the 2017 Nuugaatsiaq tsunami. The village in Greenland was partially swept by a tsunami created by a landslide that fell into the Karrat Fjord.

We carried out laboratory experiments to understand how the wave characteristics are related to the landslide features. Emphasis was put on slide-water interactions and efficiency of momentum transfers between the two media. We manufactured granular slides made of differently sized particles using plasticine clay, whose density is close to that of real-world materials. The granular mixture could be shaped, which made it possible to study how the leading edge’s shape affected momentum transfer. The mixture was initially placed in a reservoir upstream of a chute, which entered into a water basin. The angle of chute and water depth were kept constant in all our experiments, whereas the material properties and volume were varied systematically. Wave amplitudes and heights were determined from the free-surface variations, which were recorded using a high-speed camera. The velocity field within the water basin was measured using Particle image velocimetry (PIV).  

To compare the waves generated by slides exhibiting different properties, empirical equations for prediction of wave characteristics were used. We discuss the differences between experimental results and predictions based on empirical equations. Among other things, we found that the lower the material’s permeability, the larger the wave amplitude.

Chat time: Wednesday, 6 May 2020, 16:15–18:00

Chairperson: Alberto Armigliato
D1899 |
EGU2020-20733
Paola Bacigaluppi, Robert M. Boes, and David F. Vetsch

When simulating tsunamis, one of the major questions that arises in the coastal community is whether a certain set of equations is adequate to predict the behavior of generated waves and their effective impact on the shoreline. This aspect has been analyzed in several studies during the past decades in the context of ocean scales, focusing, for example, on the 2004 Sumatra and 2011 Tohoku events. 

Investigations concerning lake scales, which appear to be very different from ocean ones, have not been considered in-depth yet, to the authors' knowledge. Nevertheless, the urge to have ready-to-use tools to allow a prediction of possible hazardous events due to tsunamis in lakes has grown in the past decades (e.g. Laguna Palcacocha, Peru), especially due to climate warming that tends to enhance slope instabilities.

This contribution provides a sensitivity analysis on lake scales, considering different typologies of modeling equations and softwares. The goal is to allow for an overview and a quantification of possible errors that might occur for specific choices of modeling equations.
This study is part of an ongoing project that aims at investigating the workflow of the processes linked with the tsunami hazard of lakes, triggered by submerged and subaerial landslides.

D1900 |
EGU2020-4711
| Highlight
Katrina Kremer, Flavio S. Anselmetti, Paola Bacigaluppi, Robert M. Boes, Frederic M. Evers, Donat Fäh, Helge Fuchs, Michael Hilbe, Achim Kopf, Agostiny M. Lontsi, Valentin Nigg, Anastasiia Shynkarenko, Sylvia Stegmann, Michael Strupler, David F. Vetsch, and Stefan Wiemer

Tsunamis can occur in lacustrine environments, similar to marine settings. In lake settings, these tsunamis are mainly generated by mass-movement processes displacing large volumes of water, and triggered by seismic or aseismic phenomena. In Swiss lakes, several historical tsunamis are reported. Some of the most prominent examples are: the 563 AD Lake Geneva tsunami presumably caused by a rockfall-induced delta failure, the 1601 AD Lake Lucerne tsunami caused by earthquake-triggered sublacustrine mass movements, and the 1687 AD Lake Lucerne tsunami that was caused by a delta failure.

 

Nowadays, the shorelines of many Swiss lakes are densely populated and host important infrastructures. The occurrence of lake tsunamis in Switzerland is known, however, we still miss a workflow to assess the hazard related to tsunamis. Within the framework of a multidisciplinary project (Lake Tsunamis: Causes, Consequences and Hazard), funded by the Swiss National Science Foundation and the Federal Office for the Environment, we aim towards better understanding lake-tsunami processes using Swiss lakes as laboratories.

 

The major objectives of this project are to investigate a) the diverse causes of lake tsunamis, b) the geotechnical and sedimentological properties of unstable slope sediment, c) the potentially unstable sediment volumes on charged slopes, d) the wave generation, propagation and shore run-up, e) the onshore and shallow offshore tsunami deposits and d) their related hazard.

 

Since 2018, extensive field work using ocean bottom seismometers and cone penetration tests, as well as laboratory tests on sediment sample have been performed to assess the slope stability during seismic shaking on Lake Lucerne. Tsunami waves have been reproduced at laboratory scale to benchmark the numerical simulations of generation, propagation and run-up of tsunamis in lakes. To characterize and date historical and prehistorical tsunami deposits, on and off-shore sediment cores have been retrieved at Lake Lucerne, Geneva, Zurich and Sils. A first work-flow to assess the tsunami hazard related to earthquake-triggered sublacustrine mass movements is proposed. In this contribution, we will summarise the current status of this project.

D1901 |
EGU2020-1613
Jochen Woessner and Rozita Jalali Farahani

A series of large subduction interface earthquakes along the South American coast caused large tsunamis in recent years. Each of these events, such as the 2010 Mw8.8 Maule and the 2015 Mw8.3 Illapel events, provided novel insights to improve tsunami hazard and risk modeling for the region, in particular due to the amount of data collected during post-seismic/ tsunami surveys reporting on coastal deformation, tsunami inundation, and building stock damage. These data are genuinely relevant to evaluate scenario modeling results supporting general approaches to model the tsunami hazard and risk.

Despite the usefulness of rapidly determined finite-fault slip inversions for tsunami warning systems, the reliability of calculated elastic deformations along the coastline based on these models and subsequently tsunami flow depth and runup estimates might be questionable. We primarily shed light on the possible impact of using various solutions for selected historical events by performing full tsunami scenario calculation. We evaluate the inverted slip model solutions from the perspective of a tsunami modeler, i.e. we compare results of the elastic deformation modelling to observed coastal uplift and tsunami inundation against post-seismic survey data. These are important as coastal deformation strongly affects tsunami inundation results. Secondly, we compare observed data to modeled data from inverted slip distributions to solutions based on simulated slip distributions on the same fault geometries to understand the possible range of outcomes. .

Given an inverted slip distribution, we first map those onto the Slab2.0 subduction interface and then calculate stochastic slip distributions. Thereafter, vertical seafloor/coastline deformations are computed using a triangular elastic dislocation model that captures the complexities of the subduction zone geometry. The deformations serve as initial conditions to a high-resolution numerical model that simulates the tsunami wave propagation and coastal inundations. Parallel computations are applied to overcome the large numerical computational efforts needed. Variable land surface roughness based on land cover data is used to simulate the accurate hydraulics of coastal inundation.

Based on our modelling approach, we find that some published slip inversion models are deficient in modelling observed coastal deformation using an elastic deformation model. Only when including tsunami data for the inversions, these models tend to be better constrained. Without these data, finite fault slip inversions for local tsunami forecasts might be misleading in spatial inundation estimates as deformation results may be incorrect. This can happen both ways, either underestimating or overestimating tsunami inundations. While there are many additional aspects in the tsunami modelling procedure, this is an important basic aspect.

Our results show that simulating stochastic slip distributions enables to cover the range of possible deformation and inundation results well. This result underlines that this approach is a useful tool to generate local probabilistic tsunami hazard and risk models.

D1902 |
EGU2020-11048
Anna Bolshakova, Mikhail Nosov, Sergey Kolesov, Gulnaz Nurislamova, and Kirill Sementsov

Usually tsunami warning is issued if a submarine earthquake is registered of magnitude exceeding a threshold, the value of which varies depending on the region where the earthquake took place and on the earthquake depth. Being simple and fast this approach is characterized by quite a low accuracy in the tsunami run-up heights estimate. The forecast accuracy can be improved if, instead of magnitude, we use the potential energy of the initial elevation in the tsunami source, calculated taking into account the earthquake focal mechanism. Automatic system for estimate of tsunami hazard using focal mechanism (Tsunami Observer, http://ocean.phys.msu.ru/projects/tsunami-observer/) was recently developed and implemented. Focal mechanisms derived from analysis of the recorded seismic waveforms has two possible solutions, i.e. two nodal planes. Short after an earthquake it is not possible to determine automatically which of the nodal planes is in fact the fault plane.

The main purpose of this study is to reveal a difference in estimates of the potential energy of the initial elevation obtained making use of the first (NP1) and the second (NP2) nodal planes. All earthquake data including focal mechanism solutions were extracted from the Bulletin of the International Seismological Centre. Totally we processed nearly 6000 earthquakes Mw>6 occurred within the time period 1976 – 2019. All calculations were performed by means of the Tsunami Observer system. It was established that the potential energy calculated with use of NP1 (ENP1) and NP2 (ENP2) datasets can vary more than an order. However for overwhelming majority of seismic events (96.3%) the difference does not exceed two times, for significant number of events (74.1%) the difference does not exceed 1.2 times. In our presentation, we shall provide detailed description of calculation methods we use and the distribution of the ratio ENP1/ENP2. Also we shall discuss the influence of the focal depth and magnitude on the ratio ENP1/ENP2.

Acknowledgements

This work was supported by the Russian Foundation for Basic Research, projects 19-05-00351, 20-07-01098, 20-35-70038

D1903 |
EGU2020-5375
| Highlight
Amir Salaree, Yihe Huang, and Marlon Ramos

The Cascadia Subduction Zone (CSZ) is a 1,200 km plate boundary that poses the greatest seismic hazard in the Pacific Northwest United States. Cascadia tsunamis have been the primary subject of studies on tsunami scenarios along the United States west coast. However, the geographic extent as well as the final size of potential future ruptures in Cascadia are poorly known. This has caused the result of previous studies to remain mostly hypothetical and simply serve as “worst-case scenarios”.

In this study, we calculate the hazard of M7-9 earthquakes using more realistic models that systematically vary both the geographic extent and slip of the rupture. To achieve this goal, we use rupture simulations derived from locking models to provide estimates of coseismic deformation at the ocean floor, and design several rupture scenarios with variable hypocenters and rupture propagation. We then apply shallow water approximation to simulate the full tsunami waveforms and generate tsunami amplitude profiles along the Cascadia coastline. By varying the seismic moment thresholds of the rupture models, we find that regional maximum coastal amplitudes are not unique for a given rupture size. This phenomenon is mostly due to the special coastal geometry as well as the particular slip partitioning of the elongated north-south rupture. In fact, our simulations reveal that beyond a magnitude of Mw≈8.5, increasing the rupture size will not significantly vary the tsunami hazard, especially in southern Cascadia, with the central segments playing the most crucial role. This result has significant implications in identifying the main sources of tsunami hazard along the US west coast, especially as the worst-case rupture scenario does not uniquely correspond to the worst-case tsunami scenario at a given location.

D1904 |
EGU2020-10505
Alberto Armigliato, Enrico Baglione, and Stefano Tinti

The study presented here takes the move from two well-known premises in tsunami science: the slip distribution on earthquake faults is heterogeneous and, in the case of tsunamigenic earthquakes, slip heterogeneity influences significantly the distribution of tsunami run-ups, especially for near-field areas. In the perspective of tsunami early warning, a crucial issue is to obtain a reasonable slip distribution within a time significantly shorter than the time taken by the waves to impact the nearest coastlines.

When an earthquake occurs, the only information that becomes available after a few minutes concerns the location of the earthquake and its magnitude. The first finite-fault models (FFM), based on seismic/geodetic data inversion, become available several hours or even days after the earthquake origin time. In the case of tsunamigenic earthquakes, tsunami waveforms useful for inversion become available after the tsunami passage at the recording stations. From the warning perspective, the time to get FFM representations is therefore too long for the near-source coastal areas.

We propose and describe a strategy whose goal is to derive in quasi-real-time a reasonable representation of the heterogeneous slip distribution on the fault responsible for a given tsunamigenic earthquake and to forecast the run-up distribution along the nearest coastlines. The strategy is illustrated in its application to the 16 September 2015 Illapel (Chile) tsunamigenic earthquake.

Realistically, the hypocentre location and the magnitude of the event can be available within two-three minutes. Knowing the hypocentre location permits us to place the fault plane in a definite geographical reference, while the knowledge of magnitude allows to derive the fault dimension and the slip model. A key point here is that we can derive slip models only knowing the magnitude and the location of the hypocenter. Among these models, we adopt simple 2D Gaussian Distributions (GDs), representing the main asperity, whose parameters can be deduced from properly defined regression laws. The 2D-GD simple representation takes a very short time to be derived. To complete the characterization of the tsunamigenic source, focal parameters can be safely derived from seismological databases, while the position of the fault represents a trickier point, as the fault plane is not necessarily centered at the earthquake hypocentre. To take this uncertainty into account, as a first approach three faults for each slip model are considered: 1) a plane centered on the hypocentre, 2) a fault shifted northwards, 3) a fault shifted southwards.

We run tsunami simulations for each adopted slip distribution and for each fault position, and compare the results against the available observed tide-gauge and run-up data in the near-field. We compare the performance of our 2D-GD models with respect to the finite-fault models retrieved from inversion procedures, published months after the 2015 event. We demonstrate that the 2D-GD method performs very satisfactorily in comparison to more refined, non-real-time published FFMs and hence permits to produce reliable real-time tsunami simulations very quickly and can be used as an experimental procedure in the frame of operational tsunami warning systems.

D1905 |
EGU2020-6836
Kirill A. Sementsov, Mikhail A. Nosov, Sergey V. Kolesov, Viacheslav A. Karpov, Hiroyuki Matsumoto, and Yoshiyuki Kaneda

The DONET (Dense Oceanfloor Network System for Earthquakes and Tsunamis) is a submarine cabled real-time seafloor observatory network for precise earthquake and tsunami monitoring. Ten DONET observatories were in operation during the 2011 Tohoku-Oki event near the Pacific coast of Honshu Island. Each observatory was equipped with an ocean bottom pressure gauge (PG) and a three-component ocean bottom seismometer (OBS). A comparative analysis of the PG and OBS records revealed that shortly after seismic surface waves traversed the DONET region, free gravity waves were observed within the water layer. The period of these gravity waves was approximately 170 s, the peak-to-peak amplitude was approximately 3.5 cm, the length was on the order of 22 km, and the phase velocity was 134 m/s. We performed numerical simulations of the observed gravity waves using a combined 2D/3D numerical model. The ground motions required for the simulation were reconstructed from records provided by the DONET OBSs and the nearest ground-based GPS stations. The synthetic bottom pressure variations are in good agreement with the DONET PG records. The synthetic displacements of the ocean surface throughout the simulation domain showed that the observed gravity waves were excited directly above the submarine slopes. Theoretical estimates and numerical experiments revealed the generation mechanism of the observed gravity waves. The results showed that (1) horizontal, rather than vertical, bottom movements play a key role in their generation, (2) the amplitude of the excited gravity waves is determined by the amplitude of the dynamic horizontal bottom motions, while the contribution of horizontal static bottom displacements is insignificant, and (3) the amplitude of the excited gravity waves depends on the relative orientation of the slope and the propagation direction of the seismic surface waves.

The study was supported by Russian Foundation for Basic Research (projects 20-35-70038, 19-05-00351, 20-07-01098).

Sementsov, K. A., Nosov, M. A., Kolesov, S. V., Karpov, V. A., Matsumoto, H., & Kaneda, Y. (2019). Free gravity waves in the ocean excited by seismic surface waves: Observations and numerical simulations. Journal of Geophysical Research: Oceans, 124, 8468–8484. https://doi.org/10.1029/2019JC015115

Nosov, M. A., Sementsov, K. A., Kolesov, S. V., Matsumoto, H. & Levin, B. W. (2015). Recording of gravity waves formed in the ocean by surface seismic waves during the earthquake of March 11, 2011, off the coast of Japan. Doklady Earth Sciences, 461 (2), 408-413. https://doi.org/10.1134/S1028334X15040121

D1906 |
EGU2020-21209
Cipriano Escalante Sanchez, Manuel J. Castro Díaz, José Manuel González Vida, Jorge Macías Sánchez, Stefano Lorito, and Fabrizio Romano

When tsunamigenic events are simulated in deep to moderately deep waters, frequency dispersion effects may become mandatory. In the framework of dispersive systems, non-hydrostatic pressure type models have been shown to be able to describe weakly dispersive waves [2,3]. Although promising results begin to glimpse nowadays, dispersive solvers are still far from being robust, efficient and able to compute on a faster than real-time (FTRT) basis. The main difficulty that presents this type of systems is that at each time step a parabolic-elliptic problem has to be numerically solved and a high computational effort is required.

In [1] a novel weakly non-linear and weakly dispersive system that takes into account dispersive effects is presented. The main advantage is that the system is strictly hyperbolic and that any explicit numerical scheme can be applied to solve numerically the equations.

We will present new numerical results from an upgrade of the system presented in [1], considering curvature effects through a rewriting of the system in spherical coordinates. The numerical results will cover some standard field validation tests involving tsunami propagation waves. Besides, the explicit numerical scheme has been implemented exploiting the power of modern GPU architectures (CUDA). Then, numerical results along with some computational times will show that this numerical model opens a new line on tsunami simulation scenarios, using a new, efficient and accurate procedure to produce FTRT tsunami propagation including dispersive effects.

Acknowledgments: This research has been partially supported by the Spanish Government Research project MEGAFLOW (RTI2018-096064-B-C21), Universidad de Málaga, Campus de Excelencia Internacional Andalucía Tech and ChEESE project (EU Horizon 2020, grant agreement Nº 823844), https://cheese-coe.eu

[1] C. Escalante, M. Dumbser, M. Castro, An efficient hyperbolic relaxation system for dispersive non-hydrostatic water waves and its solution
with high order discontinuous galerkin schemes, Journal of Computational Physics 394 (2019) 385 – 416.

[2] C. Escalante, T. Morales, M. Castro, Non-hydrostatic pressure shallow flows: Gpu implementation using finite volume and finite difference
scheme, Applied Mathematics and Computation (2018) 631–659.

[3] Y. Yamazaki, Z. Kowalik, K. Cheung, Depth-integrated, non-hydrostatic model for wave breaking and run-up, Numerical Methods in Fluids
61 (2008) 473–497.

D1907 |
EGU2020-6900
Natalja Rakowsky, Harig Sven, Androsov Alexey, Goubier Thierry, Neuwirth Hannah, and Kersten Lucas

State of the art tsunami warning systems employ a combined approach of pre-computed scenarios and on the fly tsunami simulation in case of an event. The on the fly simulations are performed on rather coarse meshes (approx. 1km resolution), usually neglect e.g., the non-linear advection in the shallow water equations, and can deliver a reasonable estimate of the wave height at the coast within a few seconds of computation time. As in the early warning situation, the earthquake source is the major unknown, they can improve the hazard assessment compared to pre-computed scenarios based on idealized sources.

On the other hand, it requires a resolution of approximately 10m on land and the non-linear shallow water equations augmented by terms like the bottom roughness to simulate the inundation in the quality needed to derive risk maps for civil protection measures. With the simulation code TsunAWI, which employs an unstructured triangular mesh to seamlessly change the spatial resolution from a few meters in an area of interest to a few kilometers in the deep ocean, such simulations can be performed with a regional focus in less than 20min computation time.

Hence, with a coarsened resolution, a first estimate of the inundation could be provided within a few minutes, improving the near-realtime assessment of the hazard. We investigate which quality of inundation result can be achieved within a limited computation time, regarding computing platforms based on various generations of Intel Xeon from Broadwell to Cascade Lake.

This investigation is part of the EU funded LEXIS project lead by It4Innovations, Ostrava, Czech Republic. The overall aim is to build an advanced engineering platform at the confluence of HPC, Cloud and Big Data. Of particular interest is the development of time constrained workflows over HPC and cloud resources, with a pilot combining tsunami simulations and earthquake damage assessment. Fast tsunami inundation estimates are a key element of that pilot.

 

 

D1908 |
EGU2020-7412
Audrey Gailler and Daniel Giles

In the framework of operational conditions, the real time coastal modeling in near field is challenging to obtain accurate and reliable tsunami warning products for flooding hazard. Two main approaches are usually developed to generate maps of forecasting inundation and impacts for planning community response. One produces coastal predictions with run-up computation by solving numerically high-resolution forecast models in real time, taking into account all local effects. However, these runs depend on the availability of fine bathymetry/topography grids along the shore and are too time consuming in near field and operational context. The second approach is based on early prediction tools of the coastal wave amplitude calculated from empirical laws or transfer functions derived from these laws. Such tools are suitable in near field context (almost ten times faster than the high-resolution runs), but all local effects are not well taken into account and the assessment of run-up is missing. The linear approximations of coastal tsunami heights are provided very quickly, with global and conservative estimates.

Within the French Tsunami Warning Center (CENALT), a forecast method based on coastal amplification laws is being implemented. This fast prediction tool provides a coastal tsunami height distribution, calculated from the numerical simulation of the deep ocean tsunami amplitude and using a transfer function derived from the Green’s law. The method involves maps of regionalized values of the empirical correction factor function of the coastal configuration, as a way to amplify or attenuate specific local geometries. Due to a lack of tsunami observations in the NEAM basin, coastal amplification parameters are defined by trial and error regarding high resolution nested grids simulations on the basis of a set of historical and synthetic sources. A method to optimize these local amplification factors by minimizing a cost function is being developed at UCD. Comparisons are shown for several French coastal sites.

The local tsunami wave heights modeled from the extended Green’s law present a good agreement with the time-consuming high resolution models. The linear approximation is obtained within 1 min and provides estimates within a factor of two in amplitude. Although the resonance effects in harbors and bays are not reproduced and the horizontal inundation calculation needs to be studied further, this method is well suited for an early first estimate of the coastal tsunami threat forecast.

D1909 |
EGU2020-557
Martin Wronna, Utku Kânoğlu, and Maria Ana Baptista

We present a new Tsunami Runup Predictor (TRP). The TRP includes the length of the beach slope, the length of the accelerating phase of the wave plus the amplitude ratio for leading depression waves.

We use numerical and analytical tools to compute the runup for a dataset of 210 initial tsunami waveforms. In our tests, the slope angle of the beach varies between 1 and 5 degrees and the distance of the initial wave to the coast varies between 50 and 360 km. The results show a high correlation between the TRP and the dimensionless runup, enabling the definition of an empirical formula to predict the runup.

We further test the empirical formula using a set of past events with field data. The comparison of the empirical estimates with the runup measurements of post-tsunami surveys gives promising results.

The TRP allows estimating the tsunami runup in real-time once the offshore waveform is known.

The capacity to predict the maximum runup along the coast in real-time and include it in routine operations of Tsunami Early Warning Systems will constitute an enormous advance.

The authors would like to acknowledge the financial support  FCT through project UIDB/50019/2020 – IDL.

D1910 |
EGU2020-18639
Sebastiano D'Amico, Matthew Agius, Daniela Farrugia, and Pauline Galea

Within the SIMIT-THARSY project, the Maltese islands are upgrading their infrastructure for real-time earthquake and tsunami monitoring. The addition, through the project, of further broadband seismic stations to the Malta Seismic Network (MSN), managed by the Seismic Monitoring and Research Group (SMRG) of the University of Malta, has greatly improved the coverage for earthquake observations. The MSN now consists of eight broadband stations which will all feature online transmission, while a further three stations are planned. This upgrading means that smaller magnitude earthquakes occurring in all areas around the Maltese islands can be better detected and located. Such seismicity and microseismicity, although not generally presenting a threat to the islands, is helping to understand the nature and configuration of active faults on- and offshore the Maltese islands, which could potentially generate larger- magnitude events. Real-time earthquake monitoring, archiving and routine processing is carried out through SeisComP3 software, which is also used to create a virtual Mediterranean network for the monitoring of seismic activity in the Mediterranean basin and beyond. Also through the SIMIT-THARSY project, the SMRG has installed the tsunami monitoring package TOAST ((Tsunami Observation And Simulation Terminal) which integrates with SeisComP3 to detect tsunamigenic earthquakes, rapidly generate wave propagation simulations and predict arrival times and wave parameters at a pre-determined set of points of interest. This system, which is now operative, will contribute information to an eventual tsunami alert and preparedness programme that will be adopted by the national Civil Protection Department. A sea-level monitoring gauge will also be installed in the study area of Marsaxlokk Bay, southeast of Malta, which will contribute to the IOC online sea-level network that is integrated into the TOAST software for tsunami verification and modelling purposes.

Within the SIMIT-THARSY programme we are also implementing a seismic and tsunami-vulnerability index survey of buildings in the study area, together with geophysical investigations, which will be used to elaborate earthquake shaking and tsunami scenarios and form part of a Web-GIS database for preparedness and emergency management. In particular, single-station ambient noise measurements and seismic array analysis have been carried out in the test sites and earthquake scenarios will be computed combining both low and high frequency simulation methods. The results will be used to integrate the decision system mechanism in support of emergency planning.

SIMIT-THARSY is funded by the INTERREG V-A Italia-Malta Operational Programme (2014 – 2020)). The project partners are the Civil Protection Departments of Sicily and Malta and the Universities of Palermo, Catania and Malta.

D1911 |
EGU2020-13990
Zili Zhou and Patrick Lynett

The nonlinear deformation and run-up of tsunami waves on a plane beach and in a constant depth section are studied numerically and analytically based on a Meshfree Shallow Water Model. Because of the strong nonlinearity on the boundary of the propagation, issues like mesh distortion and discontinuous oscillation easily happen in the traditional mesh-based methods (e.g., FVM, FDM). But in the meshfree method, the drastic nonlinear changes can be well approximated by the high spectrum.

The study region is a rectangle, and the boundary condition is homogeneous, so the model meets the spectral expansion condition. And then, the trigonometric functions of a high order and high frequency can be used to solve mesh distortion and discontinuous oscillation problems. This means that the waves are simulated by multiple overlaid wavelets, making the simulation more similar to actual scenarios. The wave height (H) and horizontal wave speeds (U, V) are described by different trigonometrical series combinations.

Analytical methods including Fourier series expansion are used in the spatial dimension. After the expansion, we have the nonlinear partial differential equations with unknown coefficients, and they are functions of time. The Finite Difference Method is used in the time dimension. We choose the semi-implicit scheme to discretize the equations. This scheme saves much time since the model does not need to calculate the inversion matrix in every time step. Without this time-consuming task, compared to traditional mesh-based methods, the meshfree method can do less work, and the result will still be better, because the meshfree method (spectral method) can still be stable with a relatively big time step, while big time steps can cause inaccurate results in traditional mesh-based methods. Also, even though the numerical method is applied in the time dimension, time is only one dimensional, which makes the results not far away from the exact solutions. Since the series (or kernel, or basis) used to describe H, U, V is the orthogonal set. And All orthogonal sets remain continuous and smooth even when they oscillate strongly at a higher order. In this way, the leading causes of the drastic change problem are reduced to: 1. the calculation error, which means we need to try different integrations and find the optimal one; 2. the time step size is not small enough, which leads to more partial analysis on the boundary.

D1912 |
EGU2020-1956
Mauricio Fuentes, Francisco Uribe, Sebastian Riquelme, and Jaime Campos

There are only a few analytical 2+1 D models for tsunami propagation, in which most of them treat the tsunami generation as an isolated part from a static deformation field, usually obtained from seismic models. This work examines the behavior of the tsunami propagation in a simple set-up including a time source function which accounts for a time description of the rupture process on the seismic source. An analytical solution is derived in the wavenumber domain, which is quickly inverted to space with the Fast Fourier Transform. The solution is obtained in closed form in the 1+1D case. The inclusion of temporal parameters of the source such as rise time and rupture velocity reveals a specific domain of slow earthquakes that enhance the tsunami amplitudes and produce non-negligible shifts on the arrival times. The obtained results confirm that amplification occurs when the rupture velocity matches the long-wave tsunami speed and the static approximation corresponds to a limit case for (relatively) fast ruptures. 

D1913 |
EGU2020-8041
Steven J. Gibbons, Manuel J. Castro Díaz, Sylfest Glimsdal, Carl Bonnevie Harbitz, Maria Concetta Lorenzino, Stefano Lorito, Finn Løvholt, Massimo Nazaria, Fabrizio Romano, Jorge Macías Sánchez, Jacopo Selva, Roberto Tonini, José Manuel González Vida, Manuela Volpe, and Malte Vöge

Probabilistic Tsunami Hazard Analysis (PTHA) is an approach to quantifying the likelihood of exceeding a specified metric of tsunami inundation at a given location within a given time interval. It provides scientific guidance for decision making regarding coastal engineering and evacuation planning. PTHA requires a discretization of many potential tsunami source scenarios and an evaluation of the probability of each scenario. The classical approach of PTHA has been the quantification of the tsunami hazard offshore, while estimates of the inundation at a given coastal site have been limited to a few scenarios. PTHA, with an adequate discretization of source scenarios, combined with high-resolution inundation modelling, has been out of reach with existing models and computing capabilities with tens to hundreds of thousands of moderately intensive numerical simulations being required. In recent years, more efficient GPU-based High Performance Computing (HPC) facilities, together with efficient GPU-optimized shallow water type models for simulating tsunami inundation, have made a regional and local long-term hazard assessment feasible. PTHA is one of the so-called Pilot Demonstrators of the EC-funded ChEESE project (Center of Excellence for Exascale Computing in the Solid Earth) where a workflow has been developed with three main stages: source specification and discretization, efficient numerical inundation simulation for each scenario using the HySEA numerical tsunami propagation model, and hazard aggregation. HySEA calculates tsunami offshore propagation and inundation using a system of telescopic topo-bathymetric grids. In this presentation, we illustrate the workflows of the PTHA as implemented for HPC applications, including preliminary simulations carried out on intermediate scale GPU clusters. Finally, we delineate how planned upscaling to exascale applications can significantly increase the accuracy of local tsunami hazard analysis.

This work is partially funded by the European Union’s Horizon 2020 Research and Innovation Program under grant agreement No 823844 (ChEESE Center of Excellence, www.cheese-coe.eu).

D1914 |
EGU2020-607
Natalia Zamora and Andrey Y. Babeyko

Historical data indicate that the Middle America subduction zone represents the primary tsunamigenic source that affects the Central American coastal areas. In recent years, the tsunami potential in the region has mainly been assessed using maximum credible earthquakes or historical events showing moderate tsunami potential. However, such deterministic scenarios are not provided with their adequate probability of occurrence. In this study, earthquake rates have been combined with tsunami numerical modeling in order to assess probabilistic tsunami hazard posed by local and regional seismic sources. The common conceptual framework for the probabilistic seismic hazard assessment has been adapted to estimate the probabilities of exceeding certain tsunami amplitudes along the Central American Pacific coast. The study area encompasses seismic sources related to the Central America, Colombia and Ecuador subduction zones. In addition to the classical subduction inter-plate events, this study also incorporates sources at the outer rise, within the Caribbean crust as well as intraslab sources. The study yields conclusive remarks showing that the highest hazard is posed to northwestern Costa Rica, El Salvador and the Nicaraguan coast, southern Colombia and northern Ecuador. In most of the region it is 50 to 80% likely that the tsunami heights will exceed 2 m for the 500 year time exposure (T). The lowest hazard appears to be in the inner part of the Fonseca Gulf, Honduras. We also show the large dependence of PTHA on model assumptions. While the approach taken in this study represents a thorough step forward in tsunami hazard assessment in the region, we also highlight that the integration of all possible uncertainties will be necessary to generate rigorous hazard models required for risk planning.

D1915 |
EGU2020-6764
Sven Harig, Natalia Zamora, Alejandra Gubler, and Natalja Rakowsky

There is a growing number of numerical models for tsunami propagation and inundation available, based on different spatial discretizations and numerical approaches. Since simulations carried out with such models are used to generate warning products in an early warning context, it is crucial to investigate differences emerging from the chosen algorithms for simulation and warning product determination. Uncertainties regarding the source determination within the first minutes after a tsunami generation might be of major concern for an appropriate warning at the coast, still, the sensitivity of warning products with respect to pre-computed simulation database contents or on-the-fly calculations are of crucial importance as well.

In this study, we investigate the performance of three models (TsunAWI, HySEA, COMCOT) in the oceanic region offshore central and northern Chile with inundation studies in Valparaíso and Viña del Mar. The investigation forms part of the tsunami component in the RIESGOS project dealing more general with multi hazard assessments in the Andes region. The numerical implementation of the models include both a finite element approach with triangular meshes of variable resolution as well as finite difference implementations with nested grids for the coastal area. The tsunami sources are identical in all models and chosen from an ensemble of events used in an earlier probabilistic study of the region. Additionally, two historic events are considered as well to validate the models against the corresponding measurements.

We compare results in virtual gauges as well as actual tide gauge locations at the Chilean coast. Inundation areas are determined with high resolution and employing the model specific wetting and drying implementations. We compare the model results and sensitivities with respect to spatial resolution and parameters like bottom friction and bathymetry  representation in the varying mesh geometries.

D1916 |
EGU2020-4021
| Highlight
Yuchen Wang, Natalia Zamora, Marco Quiroz, Kenji Satake, and Rodrigo Cienfuegos

Tsunami resonance in the bays/harbors and the continental shelf leads to amplification of the wave heights and extends the duration of wave activity. Therefore, for the early warning systems and emergency response, it is important to understand the resonance behavior and mechanism. Tsunami resonance is caused by reflection and interference of tsunami waves from the edge of a harbor or continental shelf. The resonance over continental shelf is controlled by the bathymetry characteristics, and the bay/harbor resonance is mostly due to the features of the coastline. However, quantifying the impact in Japan from transpacific sources has not been systematically conducted. In this study, we assess the tsunami resonance processes from transoceanic and local sources in the ports of Japan. We first analyze the characteristics of the resonance behavior based on past events and also generate a set of ruptures like the 1730 Valparaiso earthquake to forecast these effects in Japan for a future event along the central Chilean margin. With the synthetic earthquake sources, we are able to further characterize the area using a larger number of tsunami events.

D1917 |
EGU2020-2557
Kei Ioki, Yusuke Yamashita, and Yoshihiro Kase

Hyuga-nada region is located at the south-western part of Nankai Trough, in the Pacific Ocean. M7-class interplate earthquakes are repeatedly occurred by the subducting Philippine Sea plate beneath the Eurasian plate. The largest earthquake in this area was the 1662 Hyuga-nada earthquake (M=7.6) which occurred off Miyazaki Prefecture, south-eastern area of Kyushu region, Japan, and generated tsunami (after called the 1662 tsunami). Strong ground motion hit and many structures were broken near the coast of Miyazaki Prefecture. The tsunami heights were estimated at least 4-5 m along the coast of Miyazaki city, and more than 200 people died by the earthquake and tsunami by historical records. This region is also active area of the shallow slow earthquakes. The 1662 tsunami was much larger than tsunamis generated by usual M7-class interplate earthquakes. It is known by the 2011 Tohoku earthquake that focal area of shallow slow earthquakes also become a tsunami source area. So, we hypothesized that the 1662 unusual large tsunami was caused by the coseismically slipping of focal area of shallow slow earthquakes. We firstly constructed the fault model of the 1662 earthquake based on the recent result of geophysical observation. To examine the tsunami source of the 1662 earthquake, we surveyed the 1662 tsunami deposits in the lowland along the coast of south-eastern Kyushu region. As a result, sandy event deposits interbedded with clay (organic clay) were recognized at several surveyed points. Based on facies features, these event deposits were possibly formed by the 1662 tsunami. Numerical simulation of the tsunami was carried out using the constructed fault model. Calculated tsunami inundation area can explain distribution of the likely tsunami event deposits at Komei, Miyazaki Prefecture. Furthermore, this study compares calculated tsunami inundation areas, distribution of other surveyed tsunami deposits and tsunami heights of historical records. Tsunami source of the 1662 earthquake proposed by our study could better explain geophysical, geological and historical records.

D1918 |
EGU2020-3006
CFD simulations of tsunamis from large scale propagation up to local coastal impacts
(withdrawn)
Richard Marcer, Camille Journeau, and Kévin Pons
D1919 |
EGU2020-13940
| Highlight
Oleksandr Pylypenko, Mark Zheleznyak, Raisa Demchenko, Sergii Kivva, Maxim Sorokin, and Pavlo Dykyi

The coastal areas of three nuclear power plants (NPP) in the Tohoku region of Japan were impacted by the tsunami waves of the earthquake on 11 March 2011. The overtopping of the tsunami protective dikes of Fukushima Daiichi NPP and inundation of the NPP site was followed by the nuclear accident with a large scale environmental contamination. The site of the “sister” NPP Fukushima Daini at 10 km southward from Fukushima Daichi was also inundated by waters of similar depths; however, quick reconstruction the emergency energy supply of the reactors has prevented a nuclear accident on this site. Onagawa NPP located 115 km North-East of Fukushima Daiichi is the closest NPP to the epicenter of the earthquake – the source of tsunami waves. The tsunami protection dike of this NPP was not overtopped.

To simulate the consequences of the radioactive contamination of the coastal waters at Fukushima Daiichi NPP we use the modelling system that includes the module of the numerical solution of the nonlinear shallow water equation (SWE). This module can also be used for the modelling of tsunami propagation and inundation of the coastal areas. For the testing of the SWE module, we provided the modeling of the tsunami propagation and coastal inundation in at the coast of Miyagi and Fukushima prefectures from Onagawa to Iwaki 11 March 2011. The presented part of the work includes the results of the model verification and analyses of the dynamics of the inundation of the sites of three NPPs.

The development of the 2D model COASTOX has started after the Chernobyl accident for simulations radionuclide transport in the rivers at ChNPP (Zheleznyak et al, 1989-2000). The hydrodynamic module is based on the shallow water equations. The 2-D depth-averaged advection-diffusion equations with sink source terms are used to describe the transport of suspended sediments and radionuclide in solute and with suspended sediments. The contemporary version of COASTOX code is based on the solution of 2-D shallow water equations on unstructured triangular grids using the Finite Volume Method with the verified possibilities for the modelling of wetting-drying flows. We implement a Godunov-type flux calculation scheme with approximate HLLC or Roe methods of solving a Riemann problem. The shock waves are resolved by using TVD flux limiting. COASTOX code includes two finite-difference algorithms for the numerical solution of sediment and radionuclide transport equations: explicit and implicit. For the solution of erosion-deposition equation and bottom contamination equation source, terms in transport equations are treated implicitly. The numerical code is parallelized for the CPU multi-processors systems and GPU. The SWE module was tested for the river floodplain inundation for the number of the cases and for the simulation of the radionuclide wash off from the floodplain of the Pripyat river at Chernobyl NPP. The model was implemented for the Tohoku coast on a grid of 2 million cells. The modelling results were compared with the published tsunami gage data.  The dynamics of the inundation of three NPPs sites were analyzed.

D1920 |
EGU2020-14532
Ira Didenkulova, Andrey Kurkin, Artem Rodin, Ahmed Abdalazeez, and Denys Dutykh

The goal of this study is to investigate the effect of the bottom shape on wave runup. The obtained results have been confronted with available analytical predictions and a dedicated numerical simulation campaign has been carried out by the team. We study long wave runup on composite coastal profiles. Two types of beach profiles are considered. The Coastal Slope 1 consists of two merged plane beaches with lengths 1.2 m and 5 m and beach slopes tan α = 1:10 and tan β = 1:15 respectively. The Coastal Slope 2 also consists of two sections: plane beach with length 1.2 m and a beach slope α, which is merged with a convex (non-reflecting) beach. The latter is constructed in the way, that its total height and length remain the same as for the Coastal Slope 1.

The study is conducted with numerical (in silico) and experimental approaches.

Experiments have been conducted in the hydrodynamic flume of the Nizhny Novgorod State Technical University n.a. R.E. Alekseev. Both composite beach profiles were constructed in 2019. The Coastal Slope 1 consists of three parts made of aluminum. The plain beach part of the Coastal Slope 2 is also made of aluminum, and the convex profile consists of two parts made of curved PLEXIGLAS organic glass. The water surface oscillations are measured using capacitive and resistive wave gauges with recording frequencies of up to 80 Hz and 100 Hz respectively. Wave runup is measured by a capacitive string sensor installed along the slope.

A series of experiments on the generation and runup of regular wave trains with a period of 1s, 2s, 3s and 4s were carried out. The water level was kept constant for all experiments and was equal to 0.3 meters. Up to now, 21 experiments have been carried out (10 and 11 experiments for each Coastal Slope respectively).

A comparative numerical study is carried out in the framework of the nonlinear shallow water theory and the dispersive theory in the Boussinesq approximation.

As a result, we compare the long wave dynamics on these two bottom profiles and discuss the influence of nonlinearity and dispersion on the characteristics of wave runup. It is shown numerically that, in the framework of the nonlinear shallow water theory, the runup height on the Coastal Slope 2 tends to exceed the corresponding runup height on the Coastal Slope 1, that also agrees with our previous results (Didenkulova et al. 2009; Didenkulova et al. 2018). Taking dispersion into account leads to an increase in the spread in values of the wave runup height. As a consequence, individual cases when the runup height on the Coastal Slope 1 is higher than on the Coastal Slope 2 have been observed. In experimental data, such cases occur more often, so that the advantage of one slope over another is no longer obvious. Note also that the most nonlinear breaking waves with a period of 1s have a greater runup height on Coastal Slope 2 for both models and most experimental data.

D1921 |
EGU2020-13420
| Highlight
Carlos Sánchez-Linares, Jorge Macías, Íñigo Aniel-Quiroga, Ignacio Aguirre-Ayerbe, Mauricio González, and Bernardo Aliaga
The Intergovernmental Coordination Group for the Tsunami and other Coastal Hazards Warning System for the Caribbean and Adjacent Regions (ICG/CARIBE EWS) was established in 2005 as a subsidiary body of the IOC-UNESCO with the purpose of providing efficient assistance on tsunami risk reduction to Member States in the Caribbean region after the lessons learnt from the 2004 Indian Ocean tsunami.
 
The aim of the work that we present here, is strengthen the capacities of early warning and response for tsunamis in the Caribbean through the development of community-level tsunami inundation maps for select coastal communities and a technical guide; both to support their preparation for and response to tsunamis. The selected communities under study are in Antigua and Barbuda, Barbados, Dominican Republic, St. Vincent and the Grenadines, and Trinidad and Tobago.
 
To this end, we use Tsunami-HySEA model, developed by EDANYA Group, which implements in the same code the three phases of an earthquake generated tsunami: generation, propagation and coastal inundation. At the same time it is implemented in nested meshes with different resolution and multi-GPU environment, which allows much faster than real time simulations. Due to this advantage it can produce a 4 h simulation in a 60 arcsec resolution grid for the whole Caribbean Sea in less than 4 min with a single general-purpose GPU.
 
Once provided the seismic parameters to reproduce the main scenarios that could affect to the nominated communities, and the topobathymetry data available from the study area, an exhaustive process of construction of 4 levels nested meshes was performed for each localization. Secondly, the events are simulated in order to obtain, among others, maximum depth in coast inundation with 5 meters resolution. Finally, all of these data allow us to make a detailed inundation map as a contribution to furthering tsunami risk assessment.
 
Acknowledgements. This work was done under the auspices of IOC-UNESCO and funded by EU (DG-ECHO)
D1922 |
EGU2020-714
Büşra Çelikbaş, Duygu Tufekci Enginar, Gozde Guney Dogan, Mehmet Lutfi Suzen, Cagil Kolat, Ahmet Cevdet Yalciner, Ocal Necmioglu, Alessandro Annunziato, Marzia Santini, and Siret Bali

Turkey suffered from devastating earthquakes and faced with a considerable number of tsunamis in its past. Although, tsunamis occurred in Turkey are not catastrophic as the ones in Pacific Ocean, they may still cause substantial damage in highly populated and/or touristic coastal areas. On July 21, 2017 at 22.31 UTC, a strong earthquake in the Gulf of Gokova (Mediterranean Sea) with a magnitude (Mw) of 6.6 (KOERI) was recorded. The earthquake caused a tsunami that affected the southern coast of Bodrum, Turkey and the northern parts of Kos island, Greece. The largest tsunami run-up was about 1.9 m and observed at Gumbet Bay, Bodrum (Dogan et al., 2019). Fortunately, there were no causalities as tsunami occurred at night time when there were few people on the coast, despite summer season. However, if the same event had occurred during daytime, its impact to the coastal localities would be much higher and it would cause panic among more people.

After the 2017 Bodrum-Kos tsunami, numerical simulations based on critical worst-case tsunami scenarios are performed with NAMI DANCE numerical model. According to the simulation results, a seismic scenario based on 1956-Amorgos earthquake and a combined scenario of Gokova fault and North Datca landslide scenario which is a possible submarine landslide assumed to be triggered by the seismic mechanism of Gokova scenario, give the maximum inundation distances and flow depth values at Southern coast of Bodrum Peninsula mainly in Central Bodrum town, Gumbet Bay, Bitez Bay, Yahsi Bay and Akyarlar-Karaincir-Aspat Bays where most of the settlements and touristic facilities are located.

In this study, evacuation walk time maps are prepared for the coastal settlements at Southern Coastline of Bodrum Peninsula by using Pedestrian Evacuation Analyst Tool (PEAT) developed by Jones et al. (2014) based on the selected critical scenarios above mentioned. PEAT is a least-cost-distance (LCD) evacuation model that estimates evacuation times throughout hazard zone based on elevation, land cover, walking speed and direction of movement (Wood and Schmidtlein, 2012). The required data are gathered from international open source databases and data provided by Bodrum Municipality. The resultant pedestrian evacuation maps show time in minutes for pedestrian who aims to reach safety zone from shortest route. According to the maps, longest walk times to the safety are calculated to be 8 minutes for Central Bodrum, 3 minutes for Gumbet Bay, 4 minutes for Bitez Bay, 6 minutes for Yahsi Bay and 5 minutes for Akyarlar-Karaincir-Aspat Bays. The pedestrian evacuation times are also tested by onsite measurements. The results are compared and presented by discussions. The evacuation maps provide a base for emergency managers, planners and local decision makers during the planning of evacuation routes and preparation of emergency response plans.

Acknowledgements: This study is partly supported by Turkey Tsunami Last Mile Project Analyses JRC/IPR/2018/E.1/0013/NC with contract number 936314-IPR-2018.

Keywords: Tsunami evacuation, Least cost distance model, Pedestrian evacuation, Walk time maps

D1923 |
EGU2020-13311
Duygu Tufekci-Enginar, M. Lutfi Suzen, G. Guney Dogan, and Ahmet Cevdet Yalciner

Tsunami simulations using high resolution datasets would always resemble the results that are closer to the reality. However, high resolution airborne or spaceborne local datasets have not yet been available for many regions and acquisition of this data is costly or might not even be possible for some locations. This hard-to-reach situation of high resolution datasets obliged researchers to work with open source datasets in their studies, which forces them to cope with the uncertainties of low spatial resolution.

Tsunami numerical models require both bathymetric and topographic data in order to calculate wave propagation in the water and inundation on the land. Leaving aside the availability of reliable bathymetric data, there are different open source global Digital Elevation Model (DEM) datasets, which are freely available. ASTER GDEM, SRTM and ALOS World 3D are present global open source DEMs that have highest spatial resolution of 30 meters. These three different sources of DEMs are generated using different technologies during data acquisition and different methodologies while processing. Even if they are the best available open source datasets, they all include variable sources of differences and errors.

This study aims evaluation of the sensitivity of open source DEM datasets against high resolution DEM datasets for tsunami hazard assessment and examination of accuracy of the simulations’ results. A small area in Silivri district of Istanbul is selected as study area, where 1m resolution of topographic data is available. Tsunami simulations are performed using NAMI DANCE GPU with topography data of 1m resolution based on LiDAR measurements and topography data of 30m resolution based on ASTER GDEM, SRTM and ALOS World 3D datasets. The resulted inundation on land and flow depth distributions are plotted and discussed with comparisons.

 

Acknowledgement: MSc. Bora Yalciner and Assoc. Prof. Dr. Andrey Zaytsev are acknowledged for their contributions in developing tsunami numerical model NAMI DANCE GPU used in this study. The authors also thank Istanbul Metropolitan Municipality, Directorate of Earthquake and Ground Investigation for providing high quality data and close cooperation.

Keywords: tsunami, hazard assessment, numerical modeling, open source DEM, high-resolution DEM