NH5.1

Tsunamis : from source processes to coastal hazard and warning

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 in various domains, and also in regions where the tsunami hazard was previously underestimated.

Tsunamis with the most disastrous impacts at large distances are usually generated following large subduction earthquakes. In this session, the different disciplines used to better understand subduction earthquakes mechanics and quantify the related hazards will be addressed. This includes integrated observations, both seismological and geophysical models, as well as rock physics experiments.

Tsunami hazard can be estimated through numerical modeling, complemented with laboratory experiments. Complete databases are essential to describe 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.
This merged NH5.1/OS4.15/SM4.3 session welcomes multidisciplinary contributions covering any of the aspects mentioned here, encompassing field data, geophysical models, regional hazard studies, observation databases, numerical and experimental modeling, risk studies, real time networks, operational tools and procedures towards a most efficient warning.

Co-organized by OS4/SM4
Convener: Helene Hebert | Co-conveners: Alberto Armigliato, Ira Didenkulova, Shane Murphy, Fabrizio Romano, Valenti Sallares, Elena Spagnuolo
vPICO presentations
| Tue, 27 Apr, 09:00–12:30 (CEST)

Session assets

Session materials

vPICO presentations: Tue, 27 Apr

Chairpersons: Fabrizio Romano, Shane Murphy, Finn Løvholt
09:00–09:05
Tsunamigenic sources on subduction areas and other seismic zones
09:05–09:07
|
EGU21-8278
Emil Oynakov, Liliya Dimitrova, Lyubka Pashova, and Dragomir Dragomirov

Low-laying territories along the Black Sea coastal line are more vulnerable to the possible high (long) waves due to tsunami events caused by strong earthquakes in the active seismic regions. Historically, such events are rare in the Black Sea region, despite some scientific evidence of tsunamis and their recordings through continuous sea-level observations with tide gauges built in certain places along the coast. This study analyses seismic data derived from different international earthquake catalogues - NEIC, ISC, EMSC, IDC and Bulgarian national catalogue (1981 - 2019). A catalogue of earthquakes within the period covering the historical to the contemporary seismicity with magnitudes M ≥ 3 is compiled. The data are processed applying the software package ZMAP, developed by Stefan Wiemer (http://www.seismo.ethz.ch/en/research-and-teaching/products-software/software/ZMAP/index.html). The catalogues' completeness is calculated to assess the reliability of the historical data needed to assess the risk of rare tsunami events. The prevailing part of the earthquakes' epicentres are in the seismically active regions of Shabla, the Crimean peninsula, the east and southeast coast of the Black Sea forming six main clusters, which confirmed previous studies in the region. In these areas, several active and potentially active faults, which can generate tsunamigenic seismic events, are recognized.

Acknowledgements: The authors would like to thank the Bulgarian National Science Fund for co-funding the research under the Contract КП-СЕ-КОСТ/8, 25.09.2020, which is carried out within framework of COST Action 18109 “Accelerating Global science In Tsunami HAzard and Risk analysis” (AGITHAR; https://www.agithar.uni-hamburg.de/).

How to cite: Oynakov, E., Dimitrova, L., Pashova, L., and Dragomirov, D.: Analysis of potential seismic sources of tsunamis in the Black Sea region, using data from various catalogues, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8278, https://doi.org/10.5194/egusphere-egu21-8278, 2021.

09:07–09:09
|
EGU21-8683
|
ECS
|
Highlight
Gui Hu, Wanpeng Feng, Yuchen Wang, Linlin Li, Xiaohui He, Cagil Karakas, and Yunfeng Tian

On October 30 2020 11:51 UTC, a Mw 6.9 normal fault earthquake occurred off the northern coasts of Samos Island, Eastern Aegean, Greece. Over a 120 people were killed and more than 1000 people were injured during the seismic sequence. The quake produced a moderate tsunami that swapped the coastal areas of Izmir (Turkey) and Samos (Greece) with inundation heights up to ~3 m. Finding the source of such a tsunami has been puzzling as a normal fault earthquake with Mw 6.9 would not be considered significant enough to generate metric-scale waves. Furthermore, the lack of near-field observations has made the identification of the seismogenic fault responsible for the mainshock difficult. In this study, we infer the source characteristics from multiple observation data, including InSAR, GPS, teleseismic waves and tsunami waves. We first  generate two Sentinel-1 co-seismic interferograms with a maximum Line of Sight (LOS) change of 8 cm on the coastal areas at the Samos island. We obtain a north-dipping fault model, which can slightly better explain the geodetic observations and teleseismic P waves. To understand the potential tsunami source, we use several earthquake slip models collected from different research groups to conduct tsunami simulations.  Comparing simulated tsunami waveforms with those measured at 6 local tide gauges, we show that the north-dipping fault can fit tsunami records better than the south-dipping fault. The north-dipping fault hypothesis is also further supported by the spatial distributions of the aftershocks. The spectral analysis of tsunami waveforms at selected tide gauges suggests that the tsunami period band is within 4.6 ~ 21.3 min and the primary wave period is ~14.2 min. Using this wave period as an indirect constraint, we show that the source dimension of our slip model can produce tsunami waveforms with similar wave period. We also find high-energy wave of the Samos earthquake that lasted 20 h, and fundamental oscillation periods of Sığacık Bay are remarkably close to some dominating tsunami periods. We infer the coseismic seafloor displacement alone is not enough to create disastrous effects on coastal cities; therefore we suggest that the tsunami waves may have been amplified by local coastline and tsunami resonance with local bay, or another source, e.g. triggered landslides.

How to cite: Hu, G., Feng, W., Wang, Y., Li, L., He, X., Karakas, C., and Tian, Y.:  The source characteristics and tsunami resonance effect of the 2020 Samos earthquake in Eastern Aegean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8683, https://doi.org/10.5194/egusphere-egu21-8683, 2021.

09:09–09:11
|
EGU21-3567
|
Highlight
Mohammad Heidarzadeh, Ignatius Ryan Pranantyo, Ryo Okuwaki, Gozde Guney Dogan, and Ahmet Cevdet Yalciner

The 30 October 2020 tsunami in the Aegean Sea was generated by an Mw 7.0 normal-faulting earthquake at a depth of 21 km. The earthquake epicenter was near the city of Izmir (Turkey) in the Aegean Sea and left 117 fatalities in Turkey and two deaths in Greece. A moderate tsunami was generated, which attacked the nearby coast of Turkey and the north coast of Samos island, Greece.  A maximum runup height of ~3.8 m was observed in Akarca with extensive inundation at the low elevation nearshore areas of the small bays from Akarca (South) to Alacati (North) of the central Aegean coast of Turkey (field surveys by Yalciner et al., 2020). The maximum tsunami penetration was ~2500 m along Azmak streambed at Alacati, Turkey. One casualty and at least one injury were directly attributed to the tsunami in Sigacik, Turkey. The predecessors of this event were other normal-faulting events: i) Lesvos-Karaburun (Mw 6.3) earthquake (Greece-Turkey) on 12 June 2017 approximately 110 km to the North-northwest, and ii) Bodrum-Kos (Mw 6.6) earthquake (Turkey-Greece) on 20 July 2017 approximately 110 km to the south-southeast of the epicenter of the 30 October 2020 event. The events of 2017 and 2020 show high similarities in terms of faulting mechanism and tsunami-genesis. The tsunami generated by the last event caused extensive loss of properties and damage to marine vessels. Here, we study the 30 October 2020 tsunami through analysis of eight tide gauge records as well as numerical simulations. Tide gauge data revealed that the tsunami’s zero-to-crest amplitudes, on tide gauges, was in the range of 5 – 12 cm with maximum amplitude (12 cm) recorded at Kos (Greece). The tsunami duration was unusually long and varied from 20 h to 35 h. Such long tsunami oscillations are not expected from an Mw 7.0 normal-faulting tsunamigenic earthquake and can be most likely attributed to several reflections due to the confined nature of the Aegean Sea region. We conducted Fourier and Wavelet analyses to detect tsunami’s spectral characteristics. Our tsunami simulation was able to reproduce most features of the recorded waves both in terms of amplitudes and duration. This research is suported by Royal Society (UK), grant number CHL/R1/180173. 

How to cite: Heidarzadeh, M., Pranantyo, I. R., Okuwaki, R., Dogan, G. G., and Yalciner, A. C.: Characteristics of the 30 October 2020 Mw 7.0 Aegean Sea earthquake from sea level data analysis and numerical modeling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3567, https://doi.org/10.5194/egusphere-egu21-3567, 2021.

09:11–09:13
|
EGU21-4582
|
ECS
Ignatius Ryan Pranantyo, Athanasius Cipta, Hasbi Shiddiqi, and Mohammad Heidarzadeh

An M7.0 earthquake followed by moderate tsunami destructed Majene region, western Sulawesi on 23 February 1969. This event claimed at least 64 lives and caused severe damage to infrastructure. In this study, we reconstructed the earthquake and tsunami source of this event by optimising macroseismic and tsunami dataset reported as well as analysed the earthquake focal mechanism. We estimated that the maximum intensity of the earthquake was VIII (in Modified Mercalli Intensity). From the first motion polarity analysis, the earthquake had a thrust mechanism which was plausibly from the Makassar Thrust. Further, deterministic ground motion modelling successfully fits the intensity data. However, thrust earthquake from the Makassar Thrust was unable to reconstruct 4 m tsunami height observed at Pelattoang. The estimated ratio between maximum tsunami run-up height and lateral distribution distance (I2) from the dataset indicates that the tsunami was generated by a local coastal landslide.

(This study is funded by the Royal Society (UK) grant number CHL/R1/180173)

How to cite: Pranantyo, I. R., Cipta, A., Shiddiqi, H., and Heidarzadeh, M.: Source reconstruction of the 1969 Sulawesi, Indonesia earthquake and tsunami, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4582, https://doi.org/10.5194/egusphere-egu21-4582, 2021.

09:13–09:15
|
EGU21-4983
|
ECS
Enrico Baglione, Alessandro Amato, Beatriz Brizuela, Hafize Basak Bayraktar, Stefano Lorito, Alessio Piatanesi, Fabrizio Romano, Roberto Tonini, Manuela Volpe, and Roberto Basili

We present a tsunami source solution for the 2nd May 2020, Mw 6.6 earthquake that occurred about 80 km offshore south of Crete on the shallow portion of the Hellenic Arc Subduction Zone (HASZ). This earthquake generated a small local tsunami recorded by the Ierapetra tide gauge on Crete island's southern coast. We used these single-marigram data to constrain the main features of the causative rupture. We modelled synthetic tsunami waveforms and measured their misfits with the observed data for each set of source parameters, scanned systematically around the values constrained by some of the available moment tensors.

In the attempts to discriminate between the two auxiliary fault planes of the moment tensor solutions, our results identify a shallow highly-dipping back-thrust fault as the source of this earthquake with the lower misfit. However, a rupture on a lower angle fault, possibly a splay fault of the subduction interface, with a sinistral component due to the oblique convergence on this segment of the HASZ, cannot be ruled out.

These results are relevant in the framework of the tsunami hazard assessments and Tsunami Early Warning Systems. In these frameworks, in addition to the subduction interface and possible ruptures on splay faults, other rupture types, such as those on secondary structures of the considered subduction system, cannot be excluded a priori. This circumstance bears important consequences because, as well as splay faulting, back thrust faulting might enhance the tsunamigenic potential where the subduction itself is less tsunamigenic due to the oblique convergence.

How to cite: Baglione, E., Amato, A., Brizuela, B., Bayraktar, H. B., Lorito, S., Piatanesi, A., Romano, F., Tonini, R., Volpe, M., and Basili, R.: Optimization of the fault plane and coseismic slip from tide-gauge data for the 2nd May 2020 Ierapetra, Crete, Earthquake (Mw 6.6) and the associated tsunami, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4983, https://doi.org/10.5194/egusphere-egu21-4983, 2021.

09:15–09:17
|
EGU21-5006
|
ECS
|
Highlight
Marilia Gogou, Ioanna Triantafyllou, Spyridon Mavroulis, Efthimis Lekkas, and Gerassimos A. Papadopoulos

On October 30, 2020, an Mw=7.0 earthquake occurred offshore northern Samos Island (Eastern Aegean, Greece). It was felt over a large area extending from Samos to Peloponnese in Greece and from Izmir to Istanbul in Turkey. It triggered many earthquake environmental effects and damage to buildings resulting in 119 fatalities in both countries. Among the triggered phenomena, tsunami waves with maximum height ~3.35 m struck mainly the northern coastal part of Samos Island and then other islands in the Aegean Sea including Chios, Andros, Ikaria Islands, and the western coast of Turkey.

In order to assess the tsunami intensity in Samos Island, the Integrated Tsunami Intensity Scale (ITIS 2012) was applied. ITIS 2012 is a recently introduced 12-grade scale ranging from I (not felt) to XII (completely devastating) and it is based on the assessment of a large number of objective criteria, grouped in six categories (physical quantities, impact on humans, impact on mobile objects, impacts on infrastructure, environmental effects and impact on structures).

In this context, the above information and data were used for the October 30, 2020 tsunami in Samos. Observations and measurements during a field survey conducted in Samos shortly after the event by the authors were mainly used for assigning intensities. Moreover, other sources included eyewitness, photos and videos from locals capturing the type and the extent of the tsunami impact as well as reports on the qualitative and quantitative tsunami properties and impact on the natural and built coastal environment were also used. Based on the recorded data and information and the guidelines for applying ITIS 2012, tsunami quantities and impact on humans, mobile objects, coastal infrastructure, the natural environment and buildings were taken into account. All available data were added and edited in a database in Geographic Information Systems (GIS) environment, specially designed for the purpose of the study. Then, the respective tsunami intensities were assigned in the studied sites. Moreover, interpolation methods have been also used in order to obtain zones of different intensity in the inundated coastal areas. The results included an ITIS 2012 intensity map of Samos Island.

Based on the assigned intensities, the October 30, 2020 tsunami is characterized as a moderate to strong event with considerable impact on all ITIS 2012 categories. The spatial distribution and the amount of the tsunami effects along the coastal area of Samos enabled the compilation of an intensity map with high resolution indicating that this scale works well for modern events with large amounts of effects and related information. Moreover, the individual criteria of the ITIS 2012 successfully complemented each other resulting in a detailed, concise and precise intensity map.

This is the first time that the ITIS 2012 is applied for a modern tsunami with large amounts of effects in the Mediterranean Region and especially the Aegean Sea. The results could be used for a more effective disaster risk management and risk mitigation strategies for tsunami in the Mediterranean Sea.

How to cite: Gogou, M., Triantafyllou, I., Mavroulis, S., Lekkas, E., and A. Papadopoulos, G.: The October 30, 2020 tsunami in the eastern Aegean Sea: Intensity mapping on Samos island based on the Integrated Tsunami Intensity Scale (ITIS 2012), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5006, https://doi.org/10.5194/egusphere-egu21-5006, 2021.

09:17–09:19
|
EGU21-14856
Valenti Sallares, Manel Prada, Alcinoe Calahorrano, Adrià Meléndez, Cesar R. Ranero, and Ingo Grevemeyer

Earthquakes rupturing up to close to subduction trenches have produced some of the largest tsunamis in history. Models indicate that the generation of these tsunamis require extraordinarily large near-trench sea-bottom displacement, but the underlying causes are disputed. They have been attributed to a wealth of factors prompting large shallow slip at the low-angle megathrust fault, the activation of steeper faults requiring smaller slip, or the triggering of ancillary energy sources. Although the postulated mechanisms are manifold, all of them coincide on the fact that the proposed causes and constraining factors are not universal but site-specific. As alternative to this local view, it has recently been proposed that the large near-trench slip could result from systematic upper-plate rock rigidity variations observed in worldwide subduction zones. Here we use a set of available controlled-source seismic data in the Middle America margin to obtain a model of upper-plate elastic rock properties across the rupture zone of the Ms7.0-Mw7.7 1992 Nicaragua tsunami earthquake. In combination with seismological data, our model shows that not only the required large shallow slip to generate the tsunami despite the moderate magnitude, but also the observed slow rupture propagation, long duration, high-frequency depletion, and magnitude discrepancy of this event, are all intrinsic physical attributes of near-trench rupture. The existence of a causal link between shallow slip and seismic record characteristics opens up new possibilities for tsunami early warning.

How to cite: Sallares, V., Prada, M., Calahorrano, A., Meléndez, A., Ranero, C. R., and Grevemeyer, I.: The causal link of large shallow slip, long duration and moderate shaking of the Nicaragua 1992 tsunami earthquake, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14856, https://doi.org/10.5194/egusphere-egu21-14856, 2021.

09:19–09:21
|
EGU21-13274
Nadaya Cubas, Philippe Agard, and Roxane Tissandier

Predicting the spatial extent of mega-earthquakes is an essential ingredient of earthquake hazard assessment. In subduction zones, this prediction mostly relies on geodetic observations of interseismic coupling. However, such models face spatial resolution issues and are of little help to predict full or partial ruptures of highly locked patches. Coupling models are interpreted in the framework of the rate-and-state friction laws. However, these models are too idealized to take into account the effects of a geometrically or rheologically complex plate interface. In this study, we show, from the critical taper theory and a mechanical analysis of the topography, that all recent mega-earthquakes of the Chilean subduction zone are surrounded by distributed interplate deformation emanating from either underplating or basal erosion. This long-lived plate interface deformation builds up stresses ultimately leading to earthquake nucleation. Earthquakes then propagate along a relatively smooth surface and are stopped by segments of heterogeneously distributed deformation. Our results are consistent with long-term features of the subduction margin, with observed short-term deformation as well as physical parameters of recovered subducted fragments. They also provide an explanation for the apparent mechanical segmentation of the megathrust, reconciling many seemingly contradictory observations on the short- and long-term deformation. Consequently, we propose that earthquake segmentation relates to the distribution of deformation along the plate interface and that slip deficit patterns reflect the along-dip and along-strike distribution of the plate interface deformation. Topography would therefore mirror plate interface deformation and could serve to improve earthquake rupture prediction.

How to cite: Cubas, N., Agard, P., and Tissandier, R.: Earthquake ruptures tied to long-lived plate interface deformation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13274, https://doi.org/10.5194/egusphere-egu21-13274, 2021.

09:21–09:23
|
EGU21-418
Kevin P. Furlong and Matthew W. Herman

In the 1970’s, the Shumagin Islands region of the Alaska subduction zone was identified as a seismic gap expected to host a future great (Mw >8.0) earthquake. More recent geodetic data indicate this region is poorly coupled, and the geologic record shows little evidence of past large events - leading to current thinking of the “Shumagin Gap” as a region of low seismic hazard. From July to October 2020 (with aftershocks continuing through the time of this abstract submission in January), a series of earthquakes occurred in this region, potentially incompatible with this low-coupling interpretation. The initial Mw 7.8 plate interface thrust faulting earthquake on July 21st straddled the eastern edge of the Shumagin Gap, followed by an Mw 7.6 strike-slip earthquake on October 19th within the slab under the eastern side of the Shumagin Gap. Stress modeling indicates that this strike-slip earthquake is in fact favored if the Shumagin Gap has low coupling, whereas a highly coupled Shumagin Gap would inhibit that type and location of earthquake. The initial thrust earthquake and its afterslip significantly enhanced the strike-slip stress loading within the subducting slab, helping to trigger that event. We find that although regions such as the Shumagin Gap have a low seismogenic potential for plate interface thrusting, the existence of this decoupled region increases the potential for intra-plate strike-slip faulting in association with more typical subduction earthquakes on adjacent coupled segments of the plate boundary. Therefore, the seismic and tsunami potential near these uncoupled regions might be greater than previously thought.

How to cite: Furlong, K. P. and Herman, M. W.: Triggering an Unexpected Earthquake in an Uncoupled Subduction Zone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-418, https://doi.org/10.5194/egusphere-egu21-418, 2021.

09:23–09:33
|
EGU21-8100
|
solicited
Susan Bilek and Emily Morton

Observations from recent great subduction zone earthquakes highlight the influence of spatial geologic heterogeneity on overall rupture characteristics, such as areas of high co-seismic slip, and resulting tsunami generation.  Defining the relevant spatial heterogeneity is thus important to understanding potential hazards associated with the megathrust. The more frequent, smaller magnitude earthquakes that commonly occur in subduction zones are often used to help delineate the spatial heterogeneity.  Here we provide an overview of several subduction zones, including Costa Rica, Mexico, and Cascadia, highlighting connections between the small earthquake source characteristics and rupture behavior of larger earthquakes.  Estimates of small earthquake locations and stress drop are presented in each location, utilizing data from coastal and/or ocean bottom seismic stations.  These seismicity characteristics are then compared with other geologic and geophysical parameters, such as upper and lower plate characteristics, geodetic locking, and asperity locations from past large earthquakes.  For example, in the Cascadia subduction zone, we find clusters of small earthquakes located in regions of previous seamount subduction, with variations in earthquake stress drop reflecting potentially disrupted upper plate material deformed as a seamount passed.  Other variations in earthquake location and stress drop can be correlated with observed geodetic locking variations. 

How to cite: Bilek, S. and Morton, E.: Subduction zone heterogeneity observed across the magnitude spectrum for megathrust earthquakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8100, https://doi.org/10.5194/egusphere-egu21-8100, 2021.

09:33–09:35
|
EGU21-2852
|
ECS
Manel Prada, Percy Galvez, Carlos Sanchez-Linares, Jean-Paul Ampuero, Valentí Sallarès, Jorge Macias, and Daniel Peter

It has been recently proposed that the depth-varying rupture properties of megathrust earthquakes can be explained by the depth distribution of elastic properties of the rocks overlying the megathrust fault. Here we demonstrate that such relationship is mechanically viable by using 3D dynamic rupture simulations. We compare results from two subduction zone scenarios with different depth-distribution of elastic properties to explore the influence of realistic upper-plate elasticity on rupture characteristics such as slip, rupture duration, and frequency content.

The first scenario has a homogeneous distribution of elastic properties, with values of Vp, Vs, and density typical of rocks overlying the megathrust fault at 25 km depth. The second scenario includes the typical depth distribution of elastic properties overlying the megathrust fault inferred from worldwide tomographic models of the upper plate. For both scenarios, we simulate three cases with ruptures confined to the shallow domain (0-5 km depth), transitional domain (5-10 km depth), and regular domain (10-25 km depth), respectively. We assume the same friction properties for both scenarios.

Results show that the realistic distribution of elastic properties accounts for increasing slip and decreasing high frequency content trenchwards, and that slip may be 8 times larger and corner frequency 2 times lower in the shallow domain than in the regular domain. Rupture times along depth shows that the rupture through a realistic elastic model may be 2.5-3 times slower in the shallow domain than in the regular domain. Depth-variations of slip, frequency content, and rupture time quantitatively agree with previous predictions, confirming that depletion of high frequency content and slow rupture are inherent of ruptures propagating through the shallow domain, where elastic properties variations drop more rapidly than in the regular and transitional domains.

Depth-dependent elastic properties also affect the dynamics of slip rate. Peak slip rate values in the heterogeneous model anticorrelate with rigidity variations and are 3-4 times higher than those observed in the homogeneous model in the shallow domain. Increasing peak slip-rate difference trenchwards correlates with increasing local ground motion differences between models. We also find important differences on permanent coseismic deformation of the upper plate. We show that coseismic deformation is significantly larger in the shallow domain in the heterogeneous models, where uplift ratios may be up to 2 times larger and along-dip displacement of the seafloor may be >6 times larger than displacement values from the homogeneous model. We use the permanent uplift seafloor deformation from both models to model the corresponding tsunamis with Tsunami-HySEA software. The results show that, at the coast, the maximum amplitude of the tsunami generated by the heterogeneous model may be up to 25% larger than that excited by the homogeneous model.

This study demonstrate the relevant role of upper-plate elasticity in controlling not only rupture characteristics, but also coseismic upper plate deformation, and tsunamigenesis. Neglecting the distribution of these properties may result in important underestimation of slip, rupture time, and local ground motion, as well as on seafloor coseismic deformation of the shallow domain, which in turn may lead to underestimations of tsunami size.

How to cite: Prada, M., Galvez, P., Sanchez-Linares, C., Ampuero, J.-P., Sallarès, V., Macias, J., and Peter, D.: The influence of depth-varying elastic properties in controlling the dynamic rupture of megathrust earthquakes and upper-plate coseismic deformation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2852, https://doi.org/10.5194/egusphere-egu21-2852, 2021.

09:35–09:37
|
EGU21-15257
|
ECS
Sara Aniko Wirp, Alice-Agnes Gabriel, Elizabeth H. Madden, Maximilian Schmeller, Iris van Zelst, Lukas Krenz, Ylona van Dinther, and Leonhard Rannabauer

Earthquake rupture dynamic models capture the variability of slip in space and time while accounting for the structural complexity which is characteristic for subduction zones. The use of a geodynamic subduction and seismic cycling (SC) model to initialize dynamic rupture (DR) ensures that initial conditions are self-consistent and reflect long-term behavior. We extend the 2D geodynamical subduction and SC model of van Zelst et al. (2019) and use it as input for realistic 3-dimensional DR megathrust earthquake models. We follow the subduction to tsunami run-up linking approach described in Madden et al. (2020), including a complex subduction setup along with their resulting tsunamis. The distinct variation of shear traction and friction coefficients with depth lead to realistic average rupture speeds and dynamic stress drop as well as efficient tsunami generation. 

We here analyze a total of 14 subduction-initialized 3D dynamic rupture-tsunami scenarios. By varying the hypocentral location along arc and depth, we generate 12 distinct unilateral and bilateral earthquakes with depth-variable slip distribution and directivity, bimaterial, and geometrical effects in the dynamic slip evolutions. While depth variations of the hypocenters barely influence the tsunami behavior, lateral varying nucleation locations lead to a shift in the on-fault slip which causes time delays of the wave arrival at the coast. The fault geometry of our DR model that arises during the SC model is non-planar and includes large-scale roughness. These features (topographic highs) trigger supershear rupture propagation in up-dip or down-dip direction, depending on the hypocentral depth.

In two additional scenarios, we analyze variations in the energy budget of the DR scenarios. In the SC model, an incompressible medium is assumed (ν=0.5) which is valid only for small changes in pressure and temperature. Unlike in the DR model where the material is compressible and a different Poisson’s ratio (ν=0.25) has to be assigned. Poisson’s ratios between 0.1 and 0.4 stand for various compressible materials. To achieve a lower shear strength of all material on and off the megathrust fault and to facilitate slip, we increase the Poisson ratio in the DR model to ν=0.3 which is consistent with basaltic rocks. As a result, larger fault slip is concentrated at shallower depths and generates higher vertical seafloor displacement and earthquake moment magnitude respectively. Even though the tsunami amplitudes are much higher, the same dynamic behavior as in the twelve hypocenter-variable models can be observed. Lastly, we increase fracture energy by changing the critical slip distance in the linear slip-weakening frictional parameterization. This generates a tsunami earthquake (Kanamori, 1972) characterized by low rupture velocity (on average half the amount of s-wave speed) and low peak slip rate, but at the same time large shallow fault slip and moment magnitude. The shallow fault slip of this event causes the highest vertical seafloor uplift compared to all other simulations. This leads to the highest tsunami amplitude and inundation area while the wavefront hits the coast delayed compared to the other scenarios.

How to cite: Wirp, S. A., Gabriel, A.-A., Madden, E. H., Schmeller, M., van Zelst, I., Krenz, L., van Dinther, Y., and Rannabauer, L.: 3D linked megathrust, dynamic rupture and  tsunami propagation and inundation modeling:  Dynamic effects of supershear and tsunami earthquakes , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15257, https://doi.org/10.5194/egusphere-egu21-15257, 2021.

09:37–09:39
|
EGU21-13324
|
ECS
Hafize Başak Bayraktar, Antonio Scala, Stefano Lorito, Manuela Volpe, Carlos Sánchez Linares, Gaetano Festa, Gareth Davies, Fabrizio Romano, Fabrizio Bernardi, Jacopo Selva, Jorge Macías, Marc de la Asunción, and Manuel J. Castro

Tsunami hazard depends strongly on the slip distribution of a causative earthquake. Simplified uniform slip models lead to underestimating the tsunami wave height which would be generated by a more realistic heterogeneous slip distribution, both in the near-field and in the far-field of the tsunami source. Several approaches have been proposed to generate stochastic slip distributions for tsunami hazard calculations, including in some cases shallow slip amplification (Le Veque et al., 2016; Sepulveda et al., 2017; Davies 2019; Scala et al., 2020). However, due to the relative scarcity of tsunami data, the inter-comparison of these models and the calibration of their parameters against observations is a challenging yet very much needed task, also in view of their use for tsunami hazard assessment.

Davies (2019) compared a variety of approaches, which consider both depth-dependent and depth-independent slip models in subduction zones by comparing the simulated tsunami waveforms with DART records of 18 tsunami events in the Pacific Ocean. Model calibration was also proposed by Davies and Griffin (2020).

Here, to further progress along similar lines, we compare synthetic tsunamis produced by kinematic slip models obtained with teleseismic inversions from Ye et al. (2016) and by recent stochastic slip generation techniques (Scala et al., 2020) against tsunami observations at open ocean DART buoys, for the same 18 earthquakes and ensuing tsunamis analyzed by Davies (2019). Given the magnitude and location of the real earthquakes, we consider ensembles of consistent slipping areas and slip distributions, accounting for both constant and depth-dependent rigidity models. Tsunami simulations are performed for about 68.000 scenarios in total, using the Tsunami-HySEA code (Macías et al., 2016). The simulated results are validated and compared to the DART observations in the same framework considered by Davies (2019).

How to cite: Bayraktar, H. B., Scala, A., Lorito, S., Volpe, M., Linares, C. S., Festa, G., Davies, G., Romano, F., Bernardi, F., Selva, J., Macías, J., de la Asunción, M., and Castro, M. J.: Testing Slip Models for Tsunami Generation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13324, https://doi.org/10.5194/egusphere-egu21-13324, 2021.

09:39–09:41
|
EGU21-14950
Kirill A. Sementsov, Sergey V. Kolesov, Anna V. Bolshakova, and Mikhail A. Nosov

Information on the earthquake source mechanism (Centroid Moment Tensor) becomes publicly available in a few minutes after the earthquake (for example, https://earthquake.usgs.gov/earthquakes or http://geofon.gfz-potsdam.de/eqinfo). Using this information, we can calculate the ocean bottom displacement in the earthquake area [Leonard, 2010; Okada, 1985] and then use this displacement as an input data for hydrodynamic simulation of the tsunami waves. Let us call this type of input data - Type 1. Somewhat later (and sometimes much later), than CMT, more detailed information on the rupture fault structure (Finite Fault Model) becomes available. According to Finite Fault Model, the rupture fault in the earthquake source consists of a certain number of segments characterized by their dip and strike angles. Each segment consists of a finite number of rectangular subfaults, for each of which a displacement vector, an activation time and a rise time are specified. By applying Okada's formulas to each subfault and using the principle of superposition, we can calculate the ocean bottom displacement in the earthquake area and also use it as an input data for tsunami simulations. Let us call this type of input data - Type 2. However, based on the Finite Fault Model, we are able to create a third type of input data (Type 3). To do this, it is necessary to take into account the displacement start time (subfault activation time) and the displacement duration (subfault rise time) of each subfault and consider the dynamics of the rupture process. In this case, we will be able to reconstruct not only the coseismic bottom displacement in the earthquake source (Type 2), but also describe the dynamics of the coseismic bottom displacement formation in the tsunami source (Type 3).

 

This paper compares the tsunami simulation results performed with the of different types of input data (Type 1, Type 2 and Type 3). We performed calculations for a number of large earthquakes at the beginning of the 21st century. We took all the earthquake source information from the USGS catalog (https://earthquake.usgs.gov/earthquakes). The bottom deformations of all three types were calculated using the ffaultdisp code (http://ocean.phys.msu.ru/projects/ffaultdisp/). Tsunami modeling was carried out using a combined 2D / 3D CPTM model [Nosov, Kolesov, 2019; Sementsov et al., 2019]. The simulation results are compared with each other as well as with the DART ocean bottom observatories records.

 

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

 

How to cite: Sementsov, K. A., Kolesov, S. V., Bolshakova, A. V., and Nosov, M. A.: Comparative study of the 3D tsunami simulations performed with the use of different approaches to the reconstruction of the bottom movement , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14950, https://doi.org/10.5194/egusphere-egu21-14950, 2021.

09:41–09:43
|
EGU21-15513
|
ECS
Anastasia Ivanova

Determining the tsunami source danger is currently one of the most urgent tasks. The vast majority of recorded tsunamis are of seismic origin. Part of the energy released during an earthquake passes into the energy of the initial tsunami source. The tsunami excitation efficiency depends on a number of factors: the depth of the sea above the source and its location relative to the coast and continental slope; the shape and area of residual post-seismic bottom displacements, as well as the bottom relief directly in the zone of the seismic source; inhomogeneities of the ocean floor relief along the path of tsunami propagation (for estimating wave heights in the zone farthest from the source); time inhomogeneities of tsunami wave radiation from the source zone; non-isotropy of the tsunami radiation spectrum.

To study the tsunami source efficiency, we considered three tsunamis in the Kuril ridge region: the Shikotan tsunami of 1994, and two Simushir tsunamis of 2006 and 2007. The choice of events was largely determined by the close geographical location – all of them belong to the Kuril-Kamchatka subduction zone. Also, these events are well studied, and there is quite a large amount of data on tsunami measurements onshore and in the deep ocean. At the same time, all three sources differ in the mechanisms of the seismic focus and location relative to the coast and the continental slope.

We analyzed the tsunami wave field for three events near the Russian Pacific coast. Tsunami energy flow calculations show that frontal energy flow is mainly directed to the southeast. The flux magnitude decreases with distance from the source as a result of geometric divergence and scattering. At longer distances, the effect of refraction becomes more significant – the flow is divided into separate rays due to the focusing on the irregular bottom relief.

The radiation patterns of each source that also were created show the part of wave energy that penetrated the Sea of Okhotsk through the Kuril Straits. It is easy to indicate the effect of the capture of tsunami waves by the shelf and the formation of edge waves that carry the wave energy away from the source area along the Kuril Ridge shelf. For 2006 and 2007 events a relatively small part of the wave energy went into the captured waves, but for 1994 the initial sea surface displacement area was in the shelf zone and a significant part of the energy was transferred to the captured edge waves, radiated mainly in the northeast direction.

How to cite: Ivanova, A.:  The tsunami energy radiation directivity on the example of the 1994, 2006 and 2007 events, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15513, https://doi.org/10.5194/egusphere-egu21-15513, 2021.

09:43–09:45
|
EGU21-6786
|
ECS
Rodrigo Cifuentes-Lobos, Ignacia Calisto, Cristian Saavedra, Franchesca Ormeño, Javiera San Martín, and Matías Fernandez


Probabilistic Tsunami Hazard Assessment (PTHA) brings a variety of mathematical and numerical tools for evaluating long-term exposure to tsunami related hazards in coastal communities, within which the logic tree method stands out for its usefulness in generating random slip models and dealing with epistemic and aleatory uncertainties. Key items for the stochastic study of tsunami scenarios. This method, by combining parameters that define a source model (such as magnitude, and rupture limits), allows to create a vast number of random source models that, as well as they can be used for assessing future and long-term hazard, they can also be used in conjunction with data and observations obtained from past tsunamis and earthquakes in their study.

This study proposes a numerical methodology for the generation of random tsunami source models, based on the logic tree method, for studying paleo tsunamis and historical tsunamis. In this case this methodology will be tested with data from the great Valdivia 1960 9.5 Mw earthquake and tsunami. These random source models are then filtered using empirical relations between magnitudes and rupture dimensions or rupture aspect ratios. Those models that pass this filter are then used to compute deformation using the Okada, 1985 method. This deformation fields are filtered using geodetic data and observations associated with the event of interest, eliminating all models that doesn’t satisfy these observations. In contrast, all models that pass this filter, are used as inputs to model tsunami using a staggered scheme, first modelling with low resolution topobathymetry grids, in order to assess if tsunami waves are registered in locations that are known to have been inundated and eliminate the models that do not show this behaviour. And secondly, using the deformation models that satisfy this past filter as input, high resolution grids are used to model tsunami and appraise the estimated run up of inundations and compare it with reliable historical accounts and sedimentological observations. Those models that pass all the filters mentioned above, will be subjects to statistical analysis to compare them with existent models of the Valdivia 1960 earthquake.

As it was stated above, and due to the important number of published studies, data and historical accounts, and source models available, the Valdivia 1960 9.5 Mw earthquake will be used as a benchmark to test this methodology, in order to appraise the convergence of the random models that pass every filter to the existent source models. It is important to further specify that this methodology was designed to study historical and paleo tsunamis, and will only be tested with modern tsunamis, such as Valdivia 1960.

How to cite: Cifuentes-Lobos, R., Calisto, I., Saavedra, C., Ormeño, F., San Martín, J., and Fernandez, M.: Implementation of a numerical methodology for the stochastic characterization of the Valdivia 1960 9.5 Mw tsunami source., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6786, https://doi.org/10.5194/egusphere-egu21-6786, 2021.

09:45–10:30
Break
Chairpersons: Alberto Armigliato, Valenti Sallares, Mohammad Heidarzadeh
Non Seismic Tsunamigenic Sources
11:00–11:02
|
EGU21-284
|
ECS
Ramtin Sabeti and Mohammad Heidarzadeh

Landslide-generated waves have been major threats to coastal areas and have led to destruction and casualties. Their importance is undisputed, most recently demonstrated by the 2018 Anak Krakatau tsunami, causing several hundred fatalities. The accurate prediction of the maximum initial amplitude of landslide waves (ηmax) around the source region is a vital hazard indicator for coastal impact assessment. Laboratory experiments, analytical solutions and numerical modelling are three major methods to investigate the (ηmax). However, the numerical modelling approach provides a more flexible and cost- and time-efficient tool. This research presents a numerical simulation of tsunamis due to rigid landslides with consideration of submerged conditions. In particular, this simulation focuses on studying the effect of landslide parameters on ηmax. Results of simulations are compared with our conducted physical experiments at the Brunel University London (UK) to validate the numerical model.

We employ the fully three-dimensional computational fluid dynamics package, FLOW-3D Hydro for modelling the landslide-generated waves. This software benefit from the Volume of Fluid Method (VOF) as the numerical technique for tracking and locating the free surface. The geometry of the simulation is set up according to the wave tank of physical experiments (i.e. 0.26 m wide, 0.50 m deep and 4.0 m). In order to calibrate the simulation model based on the laboratory measurements, the friction coefficient between solid block and incline is changed to 0.41; likewise, the terminal velocity of the landslide is set to 0.87 m/s. Good agreement between the numerical solutions and the experimental results is found. Sensitivity analyses of landslide parameters (e.g. slide volume, water depth, etc.) on ηmax are performed. Dimensionless parameters are employed to study the sensitivity of the initial landslide waves to various landslide parameters.

How to cite: Sabeti, R. and Heidarzadeh, M.: Preliminary results of numerical simulation of submarine landslide-generated waves, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-284, https://doi.org/10.5194/egusphere-egu21-284, 2020.

11:02–11:04
|
EGU21-12587
|
ECS
Inês Ramalho, Rachid Omira, Aldina Piedade, Davide Gamboa, José Grazina, and Luís Lemos

Slope instability is probably the most effective process shaping the seafloor of continental margins. This process often leads to the occurrence of submarine mass failures that, if large enough, can cause potential tsunamis. Yet, the dynamics of the landslide evacuated material and their induced tsunamigenic potential remain largely uncharacterized in most continental margins. This applies to the SW Iberia Margin, where large underwater landslide episodes have been evidenced.

In this work, we investigate the sensitivity of landslide-generated tsunami to the physical properties of marine sediments involved in the slope failures in the SW Iberia Margin. This includes the landslide dynamics, the tsunamigenic potential and the tsunami hazard extent. Based upon the MAGICLAND (Marine Geo-hazards Induced by Underwater Landslides in the SW Iberian Margin) project database, we select promising sizable submarine landslide scenarios. We then use an in-house developed two-layer numerical code (based on a Bingham visco-plastic model for the landslide and a non-linear shallow water model for the tsunami) to simulate both the landslide dynamics and the induced tsunami generation and propagation.

In a first stage, the numerical simulations are done considering uncertain sediments properties deduced from the literature. Next, we perform numerical simulations of the selected landslide scenarios using accurate geotechnical properties (mainly the in-situ shear strength obtained from undisturbed samples) determined by laboratory tests conducted on from the analysis of available marine gravity cores in the SW Iberian Margin. Results show that the geotechnical parameters significatively influence the simulation results of both the landslide dynamics and induced tsunami. Particularly, we noticed major effects on the landslide downslope deformation, failure speed, deposited thickness and run-out, which considerably control the momentum transferred to the generated tsunami wave. This demonstrates that the use of inappropriate material properties leads to a misquantification of landslide tsunamigenesis and hazard extent.

This work was financed by national funds through FCT—Portuguese Foundation for Science and Technology, I.P., under the framework of the project MAGICLAND – Marine Geo-hazards Induced by Underwater Landslides in the SW Iberian Margin (PTDC/ CTA-GEO/30381/2017).

How to cite: Ramalho, I., Omira, R., Piedade, A., Gamboa, D., Grazina, J., and Lemos, L.: Submarine landslide tsunamis in SW Iberia Margin: Sensitivity of tsunamigenic potential and hazard extent to physical properties of marine sediments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12587, https://doi.org/10.5194/egusphere-egu21-12587, 2021.

11:04–11:06
|
EGU21-9352
|
ECS
Xiaoyi Pan, Linlin Li, Hong Phuong Nguyen, and Dawei Wang

The 109 meridian fault is located in the west of the South China Sea (SCS) connecting to the offshore Red River Shear Zone. The evolution processes of the 109 meridian fault: striking-uplifting-subsidence of adjacent basin led to a nearly 1000m sharp bathymetric difference in the offshore region of central Vietnam. Combined with the high sediment input from numerous montane rivers in the rising hinterland, the continental slope near central Vietnam possesses the ideal condition for developing submarine landslides. Seismic data indicates many submarine landslides were developed along the steep continental slope. In this study, we analyze the possible trigger mechanisms of these landslides based on the local geological background and sedimentary environment, and assess their tsunamigenic potential along the coast of the Southern Central Vietnam (SCV). We point out that the landslide failures in this region could be triggered by several mechanisms, including seismic activities in the offshore SCV, volcanic activities, gas seep on the slope and the relative sea-level changes. The seismic and volcanic activities are related directly to the late middle Miocene volcanism generated by the change from left- to right-lateral motion on the Red River Shear Zone, showing that tectonism play a significant role in the generation of submarine landslide in the western continental slope of the SCS. To estimate the impact of tsunami waves on SCV coastline, we use two numerical models—NHWAVE and FUNWAVE-TVD to model 4 representative landslides with volume ranging between 1-4km3 and water depth of 300-1000m. The submarine landslides were treated as rigid slump and deformable slide corresponding to two different sedimentary environments. Our results show that the tsunami waves generated by rigid slump can reach up to 20m height in the landslide source area and arrive earlier to the coast of SCV than waves generated by deformable slide. Among these simulated scenarios, tsunami waves generated by the worst-case scenario arrive at the populated cities including Quy Nhơn (109.3°E,13.77°N), Tuy Hòa (109.37°E ,13.08°N) and Vung Ro Bay (109.43°E,12.86°N) in less than 25mins with maximum height of 5m. It is worth mentioning that the Vung Ro Bay will be affected by tsunami waves in all simulated scenarios. We quantify the influence of landslide characteristics (volume, water depth and material) and highlight the local effect of coastal bathymetry on the tsunami generation and propagation which lead to different hazard level of SCV coast.

How to cite: Pan, X., Li, L., Nguyen, H. P., and Wang, D.: Submarine landslides in the west continental slope of the South China Sea and their tsunamigenic potential, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9352, https://doi.org/10.5194/egusphere-egu21-9352, 2021.

11:06–11:08
|
EGU21-9485
Enrique D. Fernandez-Nieto, François Bouchut, Juan M. Delgado-Sanchez, Anne Mangeney, and Gladys Narbona-Reina

There exits in the literature many approaches that has been used to model submarine avalanches (See [5]). These models are mainly based on the pioneer work of Savage and Hutter (SH) [4] that is a shallow water type model for aerial avalanches, which is written in local coordinates, in order to simulate the tangential velocity to the bottom. A depth-averaged SH model over a general bottom with curvature was introduced in [1]. An extension to submarine avalanches is developed in [2]. In this paper the same local coordinate system is used for the two layers. Nevertheless, using a local coordinates the model would prescribe the perturbation at the surface at a wrong placement. In [3] a bilayer depth-averaged model for submarine avalanches is presented with cartesian coordinates for the water layer and local coordinates for the avalanche. The drawback is that the seabed deformation is considered as an input data for the water layer equations, then no interaction between the two fluids are taken into account and it is necessary to do an interpolation of the granular surface at each time step of the numerical simulation. In this work we present firstly the details of the proposed model, a coupled two-layer shallow water system where we consider local coordinates for the granular layer and cartesian coordinates for the fluid one. The main difference with other models that adopt the same stragie is that any interpolation of the granular surface is required. Moreover, the velocity of the granular layer has an explicit influence on the mass and momentum conservation laws of the fluid layer. Secondly, several numerical tests will be presented.

References

[1] F. Bouchut, E.D. Fernández-Nieto, A. Mangeney, and P.Y. Lagrée. On new erosion models of Savage-Hutter type for avalanches. Acta Mechanica, 199(1):181--208, 2008.
[2] E.D. Fernández-Nieto, F. Bouchut, D. Bresch, M.J. Castro Díaz, and A. Mangeney. A new Savage-Hutter type model for submarine avalanches and generated tsunami. Journal of Computational Physics, 227(16):7720--7754, 2008.
[3] P.H. Heinrich, A. Piatanesi, and H. Hébert. Numerical modelling of tsunami generation and propagation from submarine slumps: the 1998 papua new guinea event. Geophysical Journal International, 145(1):97--111, 2001.
[4] S. B. Savage and K. Hutter. The dynamics of avalanches of granular materials from initiation to runout. part I: Analysis. Acta Mechanica, 86(1):201–223, 1991.
[5] S. Yavari-Ramshe and B. Ataie-Ashtiani. Numerical modeling of subaerial and submarine landslide-generated tsunami waves-recent advances and future challenges. Landslides, 13(6):1325–1368, 2016.

How to cite: Fernandez-Nieto, E. D., Bouchut, F., Delgado-Sanchez, J. M., Mangeney, A., and Narbona-Reina, G.: A two-layer shallow flow model with two axes of integration with application to submarine avalanches and generated tsunamis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9485, https://doi.org/10.5194/egusphere-egu21-9485, 2021.

11:08–11:10
|
EGU21-10807
|
ECS
Alexandre Paris, Philippe Heinrich, and Stéphane Abadie

In the literature, OpenFOAM has been used to simulate landslide tsunamis, modeling the landslide as a solid or a two-phase flow. Here we present an approach using three phases (air, water and sediment) modeled as Newtonian fluids. This 3D model is validated against two benchmarks with deformable landslides: one subaerial (Viroulet et al. 2016) and one submarine (Grilli et al. 2017). These benchmarks are also run by a 2D depth-integrated model, AVALANCHE, recently used to reproduce the 2017 Karrat Fjord, Greenland and the 2018 Anak Krakatau, Indonesia events. Both models are able to reproduce either the water waves or the landslide behavior but not both at the same time.

Considering OpenFOAM as a reference code, sensitivity studies on the slope angle, the landslide viscosity and the landslide initial submergence showed that AVALANCHE produces similar results for slope angles between 10 and 45°, for subaerial or close to the surface landslide and/or for low viscosity values. In the other cases (submarine landslides and higher viscosity values) results indicated that OpenFOAM should be preferred to a 2D depth-integrated model.

 

References:

Grilli, S., Shelby, M. & Kimmoun, O. (2017), ‘Modeling coastal tsunami hazard from submarine mass failures: effect of slide rheology, experimental validation, and case studies off the US East Coast’, Natural Hazards 86, 353-391.

Viroulet, S., Sauret, A., Kimmoun, O. & Kharif, C. (2016), Tsunami waves generated by cliff collapse: comparison between experiments and triphasic simulations, in E. Pelinovsky & C. Kharif, eds, ‘Extreme Ocean Waves’, Springer International Publishing, Cham, pp. 173-190.

How to cite: Paris, A., Heinrich, P., and Abadie, S.: Using OpenFOAM for landslide tsunamis modeling and comparison with a 2D depth-integrated model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10807, https://doi.org/10.5194/egusphere-egu21-10807, 2021.

11:10–11:12
|
EGU21-14223
|
Highlight
Finn Løvholt, Matthias Rauter, Thomas Zengaffinen-Morris, and Carl Harbitz

Landslide tsunamis, despite their importance for the overall tsunami hazard, is not as well understood as earthquake tsunamis. Several uncertain factors contribute to the lack of understanding, such as the variability in the source mechanisms, the dynamics of the landslide and the tsunami generation, as well as the temporal probability of occurrence of landslide events. Here, we present an overview of research activities on landslide tsunami analyses in the H2020 ITN-SLATE project. This research originates from two PhD student projects within SLATE, which have so far resulted in at least six publications with several more in the pipeline. In the SLATE project, we show that both translational and rotational dynamic attributes of the landslide are good indicators of the tsunamigenic potential of slumps using the visco-plastic landslide model BingClaw, by correlating the acceleration times mass and also angular momentum with the induced tsunami height. Moreover, we have employed Navier-Stokes simulations to hindcast model experiments of subaerial landslide tsunamis. By using the experience modelling this benchmark to model tsunamis in many other geometrical settings, the Navier-Stokes model is further employed to test generality and discuss several existing parametric relationships from literature so far available only empirically. New 3D formulations for granular landslide dynamics have further been established. Numerical models have also been set up to simulate real cases such as Anak Krakatoa. Finally, a broad parametric study that constrain the landslide dynamics for a landslide probabilistic hazard analysis is undertaken, to show how using past observations can effectively reduce uncertainties related to landslide dynamics. Combining an overview of the study with some highlights, we show how SLATE has contributed to increasing our understanding of landslide tsunamis and their hazard. We also discuss how the outcome of this project provides a platform for further research. This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 721403.

How to cite: Løvholt, F., Rauter, M., Zengaffinen-Morris, T., and Harbitz, C.: Landslide tsunamis, from origin to hazard, an overview from the SLATE project, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14223, https://doi.org/10.5194/egusphere-egu21-14223, 2021.

11:12–11:14
|
EGU21-5363
|
ECS
Chao Hu, Xiao-liang Wang, and Qing-quan Liu

The calving of large-scale icebergs into the sea can generate a local tsunami that may threaten coastal communities or passing ships. A three-dimensional smoothed particle hydrodynamics model of rigid-body–fluid system is established to simulate the spatial wave generated by calving iceberg. The model is tested with simulated waves induced by a cube iceberg fall into the water body. Good agreement is obtained between simulation results and experimental data. The generation and evolution processes, and the near flow-field characteristics of the waves are analyzed. The simulation results show that waves generated in iceberg calving can generate not only a huge leading wave but also notable tailing waves. The initial propagation direction of the leading wave is determined by iceberg geometry, but as the leading wave propagates away, the water level displacement gradually develops into a semicircle wavefront which is irrelevant to iceberg geometry.

How to cite: Hu, C., Wang, X., and Liu, Q.: A Three-dimensional SPH Simulation of Iceberg Calving generated Waves, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5363, https://doi.org/10.5194/egusphere-egu21-5363, 2021.

Tsunami Hazard and Risk
11:14–11:16
|
EGU21-8027
Aaron Sweeney, George Mungov, and Lindsey Wright

The U.S. National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information (NCEI) archives analog and digital coastal water level data and ocean-bottom pressure data, digitizes select analog data, and performs quality-control and tidal analysis of these data.  The analog tide gauge records (marigrams) cover selected tsunami events between 1854 and 1981 observed at stations across the globe.  There are 3,486 high-resolution scanned marigrams in the archive.  The digital tide gauge data, primarily U.S. stations, have been collected at 1-minute sampling since 2008.  The ocean-bottom pressure data have been collected since 1983.  These time-series data are complementary to the maximum wave heights recorded in the NCEI/World Data Service Global Historical Tsunami Database.  With the introduction of visual timeline inventories, our NOAA partners have helped us identify, recover, and backfill gaps in our archive.  All water level data and products are converted to standardized file formats to reduce barriers to re-use. We provide quality-controlled water level data, computed astronomical tides, details on the harmonic tidal analysis results, and spectra to assess the quality of the de-tiding. Researchers use the quality-controlled data to validate tsunami propagation and storm surge models.  Select scanned marigram images are digitized into numerical time-series data by hand-selecting data points along the inked tidal curves. Though automated data point selection capabilities exist, when tested, they did not accurately detect faint traces and consistently failed to correctly select the peak and trough values. Hand-selection ensured that the maximum and minimum values important across water level research would be accurately recorded. From 2016 to 2019, we have digitized 48 of these images, across ten tsunami events, into ready-to-use, digital time-series data.  In the event of a tsunami, we augment our holdings by collecting and processing data from the National Hydrographic Services in the affected regions and from the United Nations Education, Scientific and Cultural Organization Intergovernmental Oceanographic Commission (UNESCO IOC) Sea Level Stations Monitoring Facility. Currently, UNESCO IOC does not process these data. These data products are then made available via Tsunami Event Pages. 

How to cite: Sweeney, A., Mungov, G., and Wright, L.: Products and Services Available from U.S. NOAA NCEI Archive of Water Level Data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8027, https://doi.org/10.5194/egusphere-egu21-8027, 2021.

11:16–11:18
|
EGU21-9162
Natalja Rakowsky, Thierry Goubier, and Sven Harig

Based on the shallow water equations,the tsunami wave propagation in the deep ocean and an assessment of the wave height at the coast can easily be simulated online during an event. To simulate the estimated inundation, however, poses higher demands on model physics and mesh resolution. Whereas in the deep ocean, a simple balance between pressure gradient force and acceleration is sufficient for first estimates of the wave propagation, additional nonlinear factors like bottom friction and momentum advection gain importance close to the coast. For a seamless simulation of the transition from wave propagation to inundation, the finite element model TsunAWI has been developed as part of the efforts within the GITEWS project (German Indonesian Tsunami Early Warning System) and in the meantime, the code has evolved considerably with applications in several projects. The triangular mesh approach allows for large freedom in the resolution of coastline and bathymetric features, however is also numerically demanding. In the ongoing EU-project LEXIS (Large-scale Execution for Industry & Society), the simulation of earthquake and tsunami events is one of the pilot study cases and on the tsunami side puts focus on the optimization of TsunAWI on modern HPC architectures. Targeting FPGAs, an accelerator for TsunAWI is being designed. It relies on a software-distributed shared memory (S-DSM) allowing sharing of the memory between distributed nodes and the accelerator(s), and is showing that TsunAWI optimisations, namely single precision and unstructured mesh traversal, are key elements to reach high performance and efficiency. For HPC systems, an MPI parallelization was implemented, based on domain decomposition. The MPI parallel code shows good scaling, making high resolution simulations feasible during an event. The developments are evaluated in simulations of tsunami inundation in hypothetical and real events in Indonesia and Chile. It turns out that the optimized approach allows for improved fast estimates of the tsunami impact in the application cases.

How to cite: Rakowsky, N., Goubier, T., and Harig, S.: Prospects of real time tsunami inundation estimates with TsunAWI - Studies in the LEXIS project , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9162, https://doi.org/10.5194/egusphere-egu21-9162, 2021.

11:18–11:20
|
EGU21-15828
|
ECS
Tung-Cheng Ho, Shingo Watada, and Kenji Satake

We propose a ray-tracing method to solve the two-point boundary value problem for tsunamis based on the long-wave theory. In the long-wave theory, the tsunami wave velocity is proportional to the square root of water depth, which is available from global bathymetric atlases. Our method computes the shortest travel times starting from each of the two given points and calculates the local ray direction to trace the ray path. We utilize an explicit, non-iterative tracing scheme that exhibits robust results and applies to any tsunami-accessible locations, and the global-shortest travel-time path is derived. In simple and real bathymetry cases, our method demonstrates stable results with neglectable low uncertainties. The ray-tracing method is then applied to analyze the path of tsunamis from different directions to four important bays in Japan. The result shows that tsunami ray paths are significantly influenced by local bathymetry, and some crucial structures, such as trench and trough, behave as the primary routes of this region. Deploying stations near these routes will be most beneficial for tsunami early warning. The existing tsunami-observing system off the Honshu area works well for tsunamis from the east side but slightly deficient for tsunamis from the west side. The far-field ray tracing shows that tsunamis traveling from Chile to Japan through two main routes—one via north Hawaii and the other via the south— depending on the location of the source.

How to cite: Ho, T.-C., Watada, S., and Satake, K.: Tsunami Ray Tracing Method for Shortest Travel-Time Path, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15828, https://doi.org/10.5194/egusphere-egu21-15828, 2021.

11:20–11:22
|
EGU21-13218
Alberto Armigliato, Martina Zanetti, Stefano Tinti, Filippo Zaniboni, Glauco Gallotti, and Cesare Angeli

It is well known that for earthquake-generated tsunamis impacting near-field coastlines the focal mechanism, the position of the fault with respect to the coastline and the on fault slip distribution are key factors in determining the efficiency of the generation process and the distribution of the maximum run-up and inundation along the nearby coasts. The time needed to obtain the aforementioned information from the analysis of seismic records is usually too long compared to the time required to issue a timely tsunami warning/alert to the nearest coastlines. In the context of tsunami early warning systems, a big challenge is hence to be able to define 1) the relative position of the hypocenter and of the fault and 2) the earthquake focal mechanism, based only on the preliminary earthquake localization and magnitude estimation, which are made available by seismic networks soon after the earthquake occurs.

In this study, the intrinsic unpredictability of the position of the hypocenter on the fault plane is studied through a probabilistic approach based on the analysis of two finite fault model datasets (SRCMOD and USGS) and by limiting the analysis to moderate-to-large shallow earthquakes (Mw  6 and depth  50 km). After a proper homogenization procedure needed to define a common geometry for all samples in the two datasets, the hypocentral positions are fitted with different probability density functions (PDFs) separately in the along-dip and along-strike directions.

Regarding the focal mechanism determination, different approaches have been tested: the most successful is restricted to subduction-type earthquakes. It defines average values and uncertainties for strike, dip and rake angles based on a combination of a proper zonation of the main tsunamigenic subduction areas worldwide and of subduction zone geometries available from publicdatabases.

The general workflow that we propose can be schematically outlined as follows. Once an earthquake occurs and the magnitude and hypocentral solutions are made available by seismic networks, it is possible to assign the focal mechanism by selecting the characteristic values for strike, dip and rake of the zone where the hypocenter falls into. Fault length and width, as well as the slip distribution on the fault plane, are computed through regression laws against magnitude proposed by previous studies. The resulting rectangular fault plane can be discretized into a matrix of subfaults: the position of the center of each subfault can be considered as a “realization” of the hypocenter position, which can then be assigned a probability. In this way, we can define a number of earthquake fault scenarios, each of which is assigned a probability, and we can run tsunami numerical simulations for each scenario to quantify the classical observables, such as water elevation time series in selected offshore/coastal tide-gauges, flow depth, run-up, inundation distance. The final results can be provided as probabilistic distributions of the different observables.

The general approach, which is still in a proof-of-concept stage, is applied to the 16 September 2015 Illapel (Chile) tsunamigenic earthquake (Mw = 8.2). The comparison with the available tsunami observations is discussed with special attention devoted to the early-warning perspective.

How to cite: Armigliato, A., Zanetti, M., Tinti, S., Zaniboni, F., Gallotti, G., and Angeli, C.: Rapid earthquake source characterization in the context of tsunami early warning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13218, https://doi.org/10.5194/egusphere-egu21-13218, 2021.

11:22–11:24
|
EGU21-12521
Cecilia Valbonesi, Alessandro Amato, and Lorenzo Cugliari

The Italian Tsunami Alert Center of INGV (Centro Allerta Tsunami, CAT-INGV), one of the Tsunami Service Providers of NEAMTWS, has been working in the last few years for improving its warning and alerting capabilities: in recent events, initial messages have been issued between 7 and 10 minutes from the earthquakes. Other improvements of the upstream component of the TWS are being implemented. However, it is well known that the most critical part of the warning system is the so-called “last mile”, meaning the step of informing residents and tourists about the impending inundation. Therefore, a large effort is needed to fill this gap, and scientists are called to give their contribution in it. 

Among the ongoing activities to reach this objective, one of the most recent is the implementation of the Tsunami Ready (TR) Program in cooperation with Italian Civil Protection Department. TR is a virtuous model for dealing with tsunami risk, which also has numerous implications in terms of the responsibilities that can arise from a tsunami impact on the population and the environment. 

This is for at least two reasons. First, the direct involvement of citizens in the education and information process represents a significant step change because it ensures greater awareness that translates into greater citizen responsibility in tsunami risk management. In particular, the participation of citizens in the TLB (tsunami local board) requested by TR is a key element in this bottom-up risk management process.

Secondly, the adoption of internationally accredited guidelines represents a reliable parameter for determining the behavior to be adopted by public decision-makers. Therefore, when an adverse event occurs, having followed the highest available and internationally accredited standard of caution contributes to mitigating the (possible) criminal reproach against civil protection officers charged in risk management.

 

In 2020, we have started the path towards the implementation of Tsunami Ready in three municipalities in Italy, located in areas of high to moderate tsunami hazard (namely Minturno, Latium; Palmi, Calabria; Pachino/Marzamemi, Sicily). The response of local authorities has been enthusiastic in all three cases. By the end of 2020, two of them have released official resolutions launching the start of the program, followed by articles on local newspapers.

 

 

How to cite: Valbonesi, C., Amato, A., and Cugliari, L.: Tsunami Ready in Italy: first steps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12521, https://doi.org/10.5194/egusphere-egu21-12521, 2021.

11:24–11:26
|
EGU21-14148
|
ECS
Shaswat Saincher, Sriram Venkatachalam, and Ira Didenkulova

The feasibility of generating long period waves using a piston-type wavemaker was comprehensively demonstrated in [1] for the Großer Wellenkanal (GWK) at 1:100 scale. These included regular waves, elongated solitons, N-waves as well as time-series pertaining to earthquake tsunamis (namely the 2004 Indian Ocean and 2011 Tohoku tsunamis).

In the companion paper [2], the aforementioned long-period waves were simulated using fully nonlinear potential theory (FNPT) and the Korteweg-de Vries (KdV) equations and compared with GWK measurements. It was established that the FNPT and KdV models accurately predicted long-distance evolution of these waves as well as dispersion-induced splitting of elongated solitons and N-waves to the form of undular bores. In addition, the run-up characteristics of the “2009 Samoa tsunami” record and elongated solitons were also studied in [2]. The semi-numerical procedure adopted in [2] for run-up estimation was limited to long non-breaking waves. However, the experimental data collection included also violently breaking focused waves of a smaller period.

In the present work, we apply IITM-RANS3D to simulate the run-up characteristics of breaking focused waves based on experiments carried out in the GWK using a 1:6 slope. An in-house, Reynolds-Averaged Navier-Stokes model (IITM-RANS3D) has been recently developed and hybridized with the in-house potential code IITM-FNPT2D. The RANS framework allows for complete description of breaking wave hydrodynamics and FNPT-hybridization ensures energy preservation for long-duration wave simulations. The run-up problem is considered as a multiphase flow where the beach is physically modelled as a high-viscosity fluid. The simulations would provide valuable insight into the run-up characteristics of breaking bores at large scale as viscous and aeration effects are fully accounted for in the RANS model.

REFERENCES

[1] S. Schimmels, V. Sriram, I. Didenkulova, Tsunami generation in a large scale experimental facility, Coastal Engineering 110, 32-41 (2016).

[2] V. Sriram, I. Didenkulova, A. Sergeeva, S. Schimmels, Tsunami evolution and run-up in a large scale experimental facility, Coastal Engineering 111, 1-12 (2016). 

How to cite: Saincher, S., Venkatachalam, S., and Didenkulova, I.: Run-up of breaking focused waves on a beach studied experimentally in a large scale facility and numerically using hybrid FNPT-RANS model , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14148, https://doi.org/10.5194/egusphere-egu21-14148, 2021.

11:26–11:28
|
EGU21-15836
|
ECS
Alisa Medvedeva and Igor Medvedev

A regional model of tsunami seismic sources in the zone of the Main Caucasian thrust has been developed. The parameters of probable models of seismic sources and their uncertainties were estimated based on the available data on historical earthquakes and active faults of the region. The scenario modeling technique was used for the tsunami zoning of the Caspian Sea coast. The time period covered by the model catalog of earthquakes used to calculate the generation and propagation of tsunamis is about 20 000 years, which is longer than the recurrence periods of the strongest possible earthquakes. The recurrence graphs of the calculated maximum tsunami heights for the entire sea coast were plotted. On their basis, the maximum heights of tsunami waves on the coast were calculated with recurrence periods of 250, 500, 1000 and 5000 years and the corresponding survey maps of the tsunami zoning of the Caspian Sea were created. The algorithm for calculating the tsunami run-up on the coast is improved, taking into account the residual (postseismic) displacements of the bottom and land relief. Estimates of tsunami hazard for the coast near the city of Kaspiysk were carried out: within the framework of the deterministic approach, the maximum wave heights and run-up distance were calculated. It is shown that the deterministic approach slightly overestimates the maximum heights of tsunami waves with certain return periods. It is shown that changes in the mean sea level can affect the features of the propagation of tsunami waves in the Caspian Sea. Thus, at an average sea level of -25-26 m, the Kara-Bogaz-Gol Bay is linked with the entire sea through a narrow strait. It leads to the propagation of tsunami waves into the water area of the bay and a decrease in wave height on the eastern coast of the sea. When the mean sea level decreases below -27 m, the positive depths in the strait disappear and water exchange through the strait stops, and the wave height in this part of the sea increases.

How to cite: Medvedeva, A. and Medvedev, I.: Tsunami Hazard of the Caspian Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15836, https://doi.org/10.5194/egusphere-egu21-15836, 2021.

11:28–11:30
|
EGU21-14159
Steven J. Gibbons, Stefano Lorito, Marc de la Asunción, Manuela Volpe, Jacopo Selva, Jorge Macías, Carlos Sánchez-Linares, Malte Vöge, Roberto Tonini, Piero Lanucara, Sylfest Glimsdal, Jan Christian Meyer, Fabrizio Romano, and Finn Løvholt

Advances in GPU-based High-Performance Computing (HPC) facilities, combined with improvements in GPU-optimized shallow water models for tsunami inundation, allow us to perform large numbers of numerical simulations of earthquake-generated tsunamis on high-resolution numerical grids. Large numbers of simulations are necessary to investigate the multi-dimensional parameter space that defines the tsunami hazard, including situations where the tsunami is generated outside major tectonic structures, where fault geometry is uncertain and can take widely different orientations. With over 1500 numerical simulations, we perform suites of systematic parameter searches to investigate the sensitivity of inundation at the towns of Catania and Siracusa on Sicily to changes both in the earthquake source parameters and in the specification of the Manning friction coefficient. The inundation is modelled using the GPU-based Tsunami-HySEA code on a system of nested topo-bathymetric grids with a finest spatial resolution of 10 meters. We consider tsunamigenesis by large earthquakes with uniform slip where the location, focal depth, fault dimensions and slip, together with the angles of strike, dip, and rake, are defined by the standard Okada parameters. We consider sources both close to the shore, in which significant co-seismic deformation occurs, and offshore, where co-seismic deformation is negligible. For the offshore earthquake sources, we see systematic and intuitive changes in the inundation with changes in strike, dip, rake, and depth. For the near-shore sources, the dependency is far more complicated and co-seismic deformation becomes significant in determining the inundation. The sensitivity studies provide clear guidelines as to the necessary resolution for source discretization for Probabilistic Tsunami Hazard Analysis, with a need for a far finer discretization of local sources than for more distant sources. For a small number of earthquake sources, we study systematically the inundation as a function of the Manning Friction Coefficient. The sensitivity of the inundation to this parameter varies greatly for different earthquake sources and topo-bathymetry at the coastline of interest. An understanding of all these dependencies is needed to better understand the consequences of tsunamigenic earthquake models with more complex geometries, and in quantifying the epistemic uncertainty in the tsunami hazard.

 

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). Computational resources made available through Sigma2/UNINETT on Saga at NTNU, Trondheim, Norway (in project nn5008k) and through PRACE on Marconi-100 at CINECA, Rome, Italy (through PRACE grant Pra21_5386/TsuHazAP).

How to cite: Gibbons, S. J., Lorito, S., de la Asunción, M., Volpe, M., Selva, J., Macías, J., Sánchez-Linares, C., Vöge, M., Tonini, R., Lanucara, P., Glimsdal, S., Meyer, J. C., Romano, F., and Løvholt, F.: The Sensitivity of Tsunami run-up to Earthquake Source Parameters and Manning Friction Coefficient in High-Resolution Inundation Simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14159, https://doi.org/10.5194/egusphere-egu21-14159, 2021.

11:30–11:32
|
EGU21-6596
Lyubka Pashova, Liliya Dimitrova, Emil Oynakov, and Vasko Galabov

Over the last two decades, in line with the global trend of expanding research into natural hazards and disaster risk reduction, the tsunami hazard and risk assessment along the coast of Europe has become a hot topic of research. In all its aspects, tsunami research includes the study of tsunami documentary evidence, historical data collection, field experiments, laboratory research, theoretical numerical and analytical modelling, and in-depth analysis of recent tsunami events. Tsunami modelling research methodologies and holistic approaches to risk assessment are continually being improved. Researches are directed to develop conventional standardised methods to analyse tsunami hazard and risk with associated uncertainties, aiming to reduce possible adverse effects on potentially vulnerable coastal settlements, coastal and marine infrastructures and natural ecosystems.

In the Black Sea, dangerous tsunami waves are a relatively rare phenomenon that cannot be forecast. Multidisciplinary studies focused on mapping and dating past events on the Black Sea coast, determining the causes, frequency of recurrence, and current prospects for tsunamis occurrence (risk) are not yet fully clarified or are in their infancy. Moreover, tsunami hazard along the Bulgarian coast is poorly understood and not considered in the National methodology for flood hazards and risk in the coastal zone. Numerical tsunami modelling performed in recent years for the region still needs to be improved. These events are relatively rare, few such cases have been documented, and validation data are scarce or missing.

This study provides a comprehensive inventory of tsunami sources from scientific publications, model studies of tsunami generated waves carried out during the recent years and an analysis of the results from recently established early warning systems in the Black Sea region. For the Bulgarian coastal zone, the results of studies of active faults with tsunamigenic potential in and around vulnerable coastal zones, available registrations at sea level during seismic events and some extreme meteorological events for the last century are summarized. A near-field and far-field tsunami sources that can generate tsunamis and affect the Bulgarian coastline are briefly reviewed. High-resolution data are needed for more credible tsunami numerical modelling for the western Black Sea region. Preliminary studies of the available datasets regarding Digital Elevation Model (DEM) and bathymetry for specific locations along the coastal zone are presented as well the needed accuracy and completeness of the data. Some consideration regarding the available and newly establish research infrastructure in the western Black Sea are also discussed.

Acknowledgements: The authors would like to thank the Bulgarian National Science Fund for co-funding the research under the Contract КП-СЕ-КОСТ/8, 25.09.2020, which is carried out within the framework of COST Action 18109 “Accelerating Global science In Tsunami HAzard and Risk analysis” (AGITHAR; https://www.agithar.uni-hamburg.de/).

How to cite: Pashova, L., Dimitrova, L., Oynakov, E., and Galabov, V.: Tsunami vulnerability along the western Bulgarian Black Sea coast - from the historical review towards multidisciplinary assessment approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6596, https://doi.org/10.5194/egusphere-egu21-6596, 2021.

11:32–11:34
|
EGU21-16064
|
ECS
Lorenzo Cugliari, Massimo Crescimbene, Andrea Cerase, Alessandro Amato, Loredana Cerbara, and Federica La Longa

The tsunami risk perception survey is promoted by the Tsunami Alert Centre of the National Institute of Geophysics and Volcanology, operating within the Italian System for Tsunami Alert (SiAM) with the Civil Protection Department and ISPRA, and acting as Tsunami Service Provider in the NEAMTWS.

Conducting studies on tsunami risk perception is important in order to obtain data on population’s knowledge and awareness, and understanding people’s perception of tsunami risk. These data are going to be added to those from two previous surveys on tsunami risk perception being issued in 2018 and 2020, to integrate the available knowledge on these issues and will provide publics, experts and policy makers with relevant tools to implement risk mitigation policies

The third phase of the survey was completed in January 2021, administering a total of 4,207 questionnaires to the population living on the coastal areas of Sicily, Campania, Latium and Sardinia, in addition to the 1,635 interviewees considered in previous surveys.

The survey used a semi-structured questionnaire consisting of 27 items, with closed alternative questions, and four sets of Likert scale questions. The questionnaire was optimized for CATI administration, taking into account the need for conciseness and comprehensibility of the questions.

All the studied regions are located in the central Mediterranean basin (including central and southern Tyrrhenian Sea, Sardinian Sea, Sicily Channel), some of which are characterized by high tsunami hazard, and in some cases they have been affected by recorded tsunamis in a close or distant past. Some regions are located in areas where potential seismic tsunami sources are present, others surround waters where active volcanoes exist, both on islands (such as Stromboli, Vulcano) and below the sea (Marsili, Palinuro). 

In addition, the four studied regions have a high risk exposure due to the high density of population living on, or visiting the coastal areas for tourism. In the areas where the questionnaire was administered, five highly populated regional capitals are located, including Palermo, Messina, Naples, Rome and Cagliari, together with other important towns (such as Catania, Siracusa, Trapani, Salerno, Olbia etc.). Moreover, the coastal shores involved in the survey, live of a significant tourist affluence in the summer period (and not only), with many tourist facilities and large hotels located along the coasts.

The survey's main aim is to analyze the perception of tsunami risk by the coastal population and to correlate levels of tsunami risk perception with scientific data from probabilistic tsunami hazard assessment (PTHA) for the considered coastal area. We will present some preliminary results of this last survey, with a comparison with the previous analyses on other regions in southern Italy.

How to cite: Cugliari, L., Crescimbene, M., Cerase, A., Amato, A., Cerbara, L., and La Longa, F.: Tsunami risk perception in Central and Southern Italy, 2021, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16064, https://doi.org/10.5194/egusphere-egu21-16064, 2021.

11:34–11:36
|
EGU21-2854
|
ECS
Pablo Poulain, Anne Le Friant, Rodrigo Pedreros, Anne Mangeney, Andrea Filippini, Anne Lemoine, Gilles Grandjean, Manuel J. Castro Díaz, and Enrique D. Fernández-Nieto

Since May 2018, Mayotte island has experienced an important seismic activity linked to the on-going sismo-volcanic crisis. The epicenters of the seismic swarms are located between 5 and 15 km east of Petite Terre for the main swarm, and 25 km east of Petite Terre for the secondary swarm. Although variations in the number of earthquakes and their distribution have been observed since the start of the eruption in early July 2018 [Lemoine A.(2020), Cesca et al.(2020)], a continuous seismicity persists and could generate several earthquakes of magnitudes close to M4 widely felt by the population. This recurrent seismicity could weaken the steep submarine slopes of Mayotte, as highlighted by the high resolution bathymetry data collected during the MAYOBS cruise in May 2019 (Feuillet et al.,submitted) and trigger submarine landslides with associated tsunamis.

To address the hazards associated with such events, we analyzed morphological data to define 8 scenarios of potential submarine slides with volumes ranging from 11,25.106 to 800.106 m3 and we simulate the landslide dynamics and generated waves. We use two complementary numerical models: (i) the code HYSEA to simulate the dynamic of the submarine granular flows and the water wave generation, and (ii) the Boussinesq FUNWAVE- TVD model simulate the waves propagation and the inundation on Mayotte. The effect of the time at which the models are coupled is investigated.

The most impacting submarine slide scenarios are located close to Petite Terre at a shallow depth. They can locally generate a sea surface elevation more than a meter in local areas especially at Petite Terre. The various simulations show that parts of the island are particularly sensitive to the risk of tsunamis. Indeed, some scenarios that does not cause significant coastal flooding still seems to cause significant hazards in these exposed areas. The barrier reef around Mayotte has a prominent role in controlling the wave propagation towards the island and therefore reducing the impact on land. It should be noted that the arrival of tsunamis on the coastline is not necessarily preceded by a retreat from the sea and the waves can reach the coasts of Mayotte very quicky (few minutes).

 

Cesca, S., Letort, J., Razafindrakoto, H.N.T. et al. Drainage of a deep magma reservoir near Mayotte inferred from seismicity and deformation. Nat. Geosci. 13, 87–93 (2020). https://doi.org/10.1038/s41561-019-0505-5

Feuillet, N, Jorry, S. J., Crawford, W, Deplus, C. Thinon, I, Jacques, E. Saurel, J.M., Lemoine, A., Paquet, F., Daniel, R., Gaillot, A., Satriano, C., Peltier, A., Aiken, C., Foix, O., Kowalski, P., Laurent, A., Beauducel, F., Grandin, R., Ballu, V., Bernard, P., Donval, J.P., Geli, L., Gomez, J. Guyader, V., Pelleau, P., Rinnert, E., Bertil, D., Lemarchand, A., Van der Woerd, J.et al. (in rev). Birth of a large volcano offshore Mayotte through lithosphere-scale rifting, Nature.

Anne Lemoine, Pierre Briole, Didier Bertil, Agathe Roullé, Michael Foumelis, Isabelle Thinon, Daniel Raucoules, Marcello de Michele, Pierre Valty, Roser Hoste Colomer, The 2018–2019 seismo-volcanic crisis east of Mayotte, Comoros islands: seismicity and ground deformation markers of an exceptional submarine eruption, Geophysical Journal International, Volume 223, Issue 1, October 2020, Pages 22–44, https://doi.org/10.1093/gji/ggaa273

How to cite: Poulain, P., Le Friant, A., Pedreros, R., Mangeney, A., Filippini, A., Lemoine, A., Grandjean, G., J. Castro Díaz, M., and D. Fernández-Nieto, E.: Numerical simulation of submarine landslide and generated tsunamis : Application to the Mayotte seismo-volcanic crisis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2854, https://doi.org/10.5194/egusphere-egu21-2854, 2021.

11:36–12:30