GM2.2 | Environmental Seismology: advancing earth surface process understanding through geophysical methods
EDI
Environmental Seismology: advancing earth surface process understanding through geophysical methods
Co-organized by CR2/GI5/SM5
Convener: Josefine Umlauft | Co-conveners: Michael Dietze, Małgorzata Chmiel, Ugo Nanni
Orals
| Mon, 24 Apr, 08:30–12:05 (CEST)
 
Room G1
Posters on site
| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)
 
Hall X3
Posters virtual
| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)
 
vHall SSP/GM
Orals |
Mon, 08:30
Mon, 14:00
Mon, 14:00
Our planet is shaped by a multitude of physical, chemical and biological processes. Most of these processes and their effect on the ground’s properties can be sensed by seismic instruments – as discrete events or ongoing signatures. Seismic methods have been developed, adopted and advanced to study those dynamics at or near the surface of the earth, with unprecedented detail, completeness and resolution. The community of geophysicists interested in earth surface dynamics and geomorphologists, glaciologists, hydrologists, volcanologists, geochemists, biologists and engineering geologists interested in using arising geophysical tools and techniques is progressively growing and collaboratively advancing that emerging scientific discipline.

When you are interested in contributing to or getting to know about the latest methodological and theoretical developments, field and lab scale experimental outcomes, and the broad range of applications in geomorphology, glaciology, hydrology, meteorology, engineering geology, volcanology and natural hazards, then this session would be your choice. We anticipate a lively discussion about standing questions in earth surface dynamics research and how seismic methods could help solving them, we will debate about community based research opportunities and are looking forward to bringing together transdisciplinary knowledge and mutual curiousity.

Topical keywords: erosion, transient, landslide, rockfall, debris flow, fracturing, stress, granular flow, rock mechanics, snow avalanche, calving, icequake, basal motion, subglacial, karst, bedload, flood, GLOF, early warning, coast, tsunami, eruption, tremor, turbidity current, groundwater, soil moisture, noise, dv/v, HVSR, fundamental frequency, polarisation, array, DAS, infra sound, machine learning, classification, experiment.

We are happy to announce Agnes Helmstetter as invited speaker!

Orals: Mon, 24 Apr | Room G1

Chairpersons: Josefine Umlauft, Małgorzata Chmiel
08:30–08:35
Ice, Water and Wind
08:35–09:05
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EGU23-16571
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solicited
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On-site presentation
agnes helmstetter

Glaciers or ice-streams have many common points with tectonic faults. Glaciers can move by

stable or unstable slip or by creep within the glacier thickness. Like faults, glacier sliding can

produce “icequake” signals over a huge range of frequencies, rupture length and signal

duration, as well as tremor. But because glaciers are shallower, the sliding interface can be

accessed directly much more easily, by boreholes or cavities. And they move much faster than

tectonic faults, so that deformation is easier to estimate and icequake inter-event times are

much shorter than for earthquakes.

Here I present some observations of high- and low-frequencies repeaters of basal icequakes

in the Mont-Blanc areas. Both types of events occur as bursts lasting for a few days or weeks,

with quasi-regularly inter-events times of the order of a few minutes or hours, and progressive

changes in amplitude and inter-event times. High-frequency events (around 50 Hz) occur all

over the year, with no clear triggering mechanism, and are located on the lower-part of

glaciers, where ice is at the melting point temperature and the glacier mainly moves by stable

sliding. Low frequency events (around 5 Hz) are mainly located at higher elevations (mainly

above 3000 m asl), on steeper slopes, and have larger magnitudes (-2<m<0). They are mainly

observed during or shortly after snowfalls. At these elevations, glaciers are possibly coldbased,

or close to the melting-point temperature, so that they are stuck to their bed and

mainly deform by creep within the ice. We observe progressive changes in waveforms that

suggest slow and evolving rupture velocities. These low-frequency icequakes may be the

analog of low-frequency earthquakes, which also occur near the transition between stable and

unstable slip.

How to cite: helmstetter, A.: Clusters of low- and high-frequency repeating icequakes in the Mont-Blanc massif, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16571, https://doi.org/10.5194/egusphere-egu23-16571, 2023.

09:05–09:15
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EGU23-12107
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ECS
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On-site presentation
Fabian Lindner, Krystyna Smolinski, Riccardo Scandroglio, Andreas Fichtner, and Joachim Wassermann

As observed elsewhere on a global scale, mountain permafrost at the Zugspitze (German/Austrian Alps) is degrading in response to climate change, which affects the rock slope stability and thus the hazard potential. Recent studies suggest that passive seismology is a promising and emerging tool to monitor permafrost changes as the seismic velocity of rocks strongly decreases/increases upon thawing/freezing. Compared to other, more classical methods like borehole temperature logging or electrical resistivity tomography (ERT), seismology is less laborious and costly, non-invasive and allows continuous monitoring. At Mt. Zugspitze, we exploit these advantages using a permanent seismic station (installed in 2006) as well as three small seismic arrays and Distributed Acoustic Sensing (DAS; both available since summer/fall 2021), to infer permafrost dynamics with high spatio-temporal resolution. The seismic data show repeating diurnal noise generated by the operation of cable cars, which we leverage for cross-correlation analysis. Our results suggest that the dominant signal in the retrieved seismic velocity change time series is caused by the seasonal freeze-thaw cycles associated with permafrost bodies on the northern side of the mountain ridge. On the long-term, the time series show a gradual velocity decrease associated with permafrost degradation due to atmospheric warming and compare well with modeled velocity change time series using rock temperature data from a nearby borehole, which intersects the mountain ridge. We discuss differences in our seismic analysis results obtained from direct and coda waves as well as from single station to station pairs and DAS and interpret the results in the light of other measurements including ERT, rock temperature logging and meteorological parameters.

How to cite: Lindner, F., Smolinski, K., Scandroglio, R., Fichtner, A., and Wassermann, J.: Seismic Monitoring of Permafrost Dynamics at Mt. Zugspitze (German/Austrian Alps), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12107, https://doi.org/10.5194/egusphere-egu23-12107, 2023.

09:15–09:25
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EGU23-16008
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ECS
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On-site presentation
Ana Nap, Fabian Walter, Adrien Wehrlé, Andrea Kneib-Walter, Guillaume Jouvet, and Martin P. Lüthi

Outlet glaciers and ice streams are the main channels through which ice sheets transport their mass towards the ocean. One of Greenland’s largest outlet glaciers Sermeq Kujalleq in Kangia (Jakobshavn Isbrae) has been broadly researched after experiencing a rapid retreat of the terminus and accompanying speedup to up to 40 m/day in the early 2000’s. However, such short-term ice dynamic variations remain poorly understood making numerical models difficult to constrain and predictions on future sea-level rise uncertain.

The short-term ice dynamics of Sermeq Kujalleq consists in transient states and can only be captured by in-situ measurements of high spatial and temporal resolution. Glacier seismology has proven to be a valuable tool to study these dynamics, it provides data with a high temporal resolution and can provide information on processes happening below the ice surface. Within the COEBELI project we combine passive glacier seismology with global navigation satellite system (GNSS) receivers, long-range drones, time-lapse cameras and terrestrial radar interferometry to capture processes such as calving and basal sliding at their respective timescales.

Here, we present results from a multi-array seismic deployment at Sermeq Kujalleq in Summer 2022. From May until September two arrays were deployed in the upstream part of the fast-flowing ice stream (>22 km from calving front) and one array on slower moving ice North of the main trunk. For a 3-week period in July, four more arrays were deployed on the fast-flowing ice stream closer to the calving front (<15 km). In the severely crevassed areas near the calving front (<15 km), the arrays consisted of custom-made autonomous seismic boxes whereas at more accessible upstream areas we installed borehole instruments. During the deployment we recorded multiple large calving events, glacier speedups and periodic multi-hour tremors accompanied by bursts of short-term high frequency (>50 Hz) icequakes. By studying these different signals, we are able to better constrain the processes and forces that control fluctuating ice-flow velocity and calving events.

How to cite: Nap, A., Walter, F., Wehrlé, A., Kneib-Walter, A., Jouvet, G., and Lüthi, M. P.: Short-term fast ice dynamics derived from passive seismic data at a large Greenland outlet glacier, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16008, https://doi.org/10.5194/egusphere-egu23-16008, 2023.

09:25–09:35
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EGU23-16346
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ECS
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On-site presentation
Wojciech Gajek

High-melt areas of glaciers generate a rich spectrum of ambient seismicity. These signals do not only contain information about the source mechanisms (e.g. englacial fracturing, water flow, iceberg detachment, basal stick-slip motion) but also carry information about seismic wave propagation within the glacier ice and, therefore, the mechanical properties of the ice. In the summer of 2021 two seismic arrays were deployed in Southern Spitsbergen at the vicinity of Hansbreen’s terminus, one being placed directly on the glacial ice, yielding an 8-days long time series of glacial seismicity.

The direct and scattered wave fields from tens of thousands of icequake records (few thousands per day) were used to determine seismic velocities and monitor structural changes within the ice, while the analysis of the ambient noise was leveraged to constrain the ice thickness. The surface icequakes dominate the seismograms due to an abundance of englacial fracturing. Hence, Rayleigh waves and beam-based techniques were employed to characterise the patterns of microseismicity at the transform junction of two glaciers (Tuvbreen and Hansbreen). Several clusters of various-origin seismicity being active at certain times are identified with a majority of them located on stagnant, fast-melting Tuvabreen.

How to cite: Gajek, W.: Rayleigh wave is the coolest – resolving microseismicity of a tidewater glacier in Svalbard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16346, https://doi.org/10.5194/egusphere-egu23-16346, 2023.

09:35–09:45
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EGU23-1601
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ECS
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On-site presentation
Anthony Abi Nader, Julie Albaric, Marc Steinmann, Clément Hibert, Jean-Philippe Malet, Benjamin Pohl, and Christian Sue

Unlike surface water reservoirs, that can be easily quantified and monitored, underground conduits in karst systems are often inaccessible, hence challenging to monitor. Seismic noise analysis was proved to be a reliable tool to monitor ground water storage in a fractured rock aquifer (Lecocq et al. 2017). In underground karstic environments, seismic noise monitoring was able to detect hydrological cycles and monitor the groundwater-content variations (Almagro Vidal et al. 2021). The following approach relies on coupling passive seismic wavefield with hydrological data in a machine learning algorithm in order to monitor underground water heights. The studied site is the Fourbanne karst aquifer (Jura Mountains, Eastern France, Jurassic Karst observatory). The underground conduit is accessible through a drilled shaft and instrumented by two 3-component seismological stations, one located underground and the other one at the surface, and a water height probe. We applied a new approach based on the machine learning random forest (RF) algorithm and continuous seismic records (Hibert et al., 2017), to find characteristic signals to predict the underground river water height. The method consists on the computation on a sliding window of seismic signal features (waveform, spectral and spectrogram features) and using the corresponding water height at the same time window to train the algorithm, and then apply it on new data. The RF algorithm is capable of accurately detecting flooding periods and reproduce the groundwater heights with an efficiency exceeding 95% and 53% using the Nash-Sutcliffe criterion for the seismic stations located in the underground conduit and at the surface respectively. The obtained results are a first promising outcome for the remote study of water circulation in karst aquifers using seismic noise.

How to cite: Abi Nader, A., Albaric, J., Steinmann, M., Hibert, C., Malet, J.-P., Pohl, B., and Sue, C.: Groundwater Heights Prediction from Seismic Waves with Machine Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1601, https://doi.org/10.5194/egusphere-egu23-1601, 2023.

09:45–09:55
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EGU23-5610
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ECS
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On-site presentation
Axelle Pantiga, Vincent Allègre, Roland Lastennet, Nicolas Houillon, Sylvain Mateo, Fabien Naessens, and Alain Denis

Karst aquifers are characterized by their heterogeneity and complex underground geometry. A great part of the world relies on karst resources for drinkable water and understanding the functioning of karst systems is essential to assess their vulnerability and response to rainfall. Relevant continuous parameters to quantify the underground flow dynamics are still required for these studies as direct underground measurements are not possible. We used surface ambient noise measurements to estimate the seismic signature and amplitude associated with the water flow within an underground karst conduit. We combined geophysical measurements with hydro-chemical and hydrogeological data to build a multidisciplinary approach. The experimental site is the Glane spring, in Dordogne (France). The hydrogeological catchment of this Vauclusian-type spring is 75 km² and consists of upper Jurassic carbonate rocks. The Glane spring shows rapid and intense variations of discharge following rainfall events, ranging from 0.1 to 4 m3/s in 2021. Ambient noise has been continuously recorded since December 2021 using four seismic stations deployed upstream of the source and above the well-known karst terminal conduit. Hydro-chemical parameters and water level have been continuously monitored during a full hydrological cycle and a rain gauge was installed on site to monitor rainfall. During the first year of monitoring, we identified six flooding events. Each event was characterized by an increase in water flow associated with an increase in the seismic signal amplitude. We observed that the seismic amplitude standard level is higher during the high-water period than during the low water period suggesting a larger base water flow. We also observed hysteresis between the seismic power and hydro-chemical parameters. Correlations between the seismic recordings and hydrochemistry might suggest a change in water flow regime within the conduit prior to the flood. Seismic power variations associated with discharge variations are similar to what was already observed for sub-glacial melting flow. Other springs and swallow holes are currently instrumented to validate the approach in the field.

How to cite: Pantiga, A., Allègre, V., Lastennet, R., Houillon, N., Mateo, S., Naessens, F., and Denis, A.: Evidence of sub-surface water flow dynamics within a karst conduit from ambient noise monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5610, https://doi.org/10.5194/egusphere-egu23-5610, 2023.

09:55–10:05
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EGU23-1046
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ECS
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On-site presentation
Haleh Karbala Ali, Christopher J. Bean, and Athena Chalari

Karst is a landscape with distinctive hydrology and landforms that arise when the underlying rock is soluble. Locating the flowing conduits and pathways in karst is important in terms of water resource management, groundwater flooding, geotechnical and engineering projects. Understanding flow pathways is particularly important for road and railway construction, so as not to adversely affect hydrological networks, in particular those associated with Turloughs.

The aim of this study was to develop methods for directly detecting energetic groundwater flow in sub-surface conduits through passive seismic applications, by detecting the small ground vibrations (seismic microtremor) that flowing water in the sub-surface may generate. This is in contrast to the current ‘traditional’ approach of attempting to actively image the conduits using geophysical and other methods, in order to determine the geometry of flow paths. The imagery of conduits in karst is a very difficult problem and determining if they contain flowing structures is also a very significant challenge using traditional methods, which is the motivation for developing a new approach to the problem.

We undertook experiments at two sites on karst in Ireland; one gently-sloping shallow conduit and one relatively deep and complex-structured conduit. We chose these sites as the caves had previously been dived and we had access to the shapefiles of these caves to ground-truth our findings.

We observed that subterranean flow-related micro-tremor in karst appears as persistent frequency bands on the spectrograms that vary with time and seismic station location with respect to the conduit. This persistent frequency is different than the soil resonating frequency and relates to the subterranean water flow in the conduits. Application of an Amplitude Location Method (ALM)  clearly delineated the conduit as the source of the micro-tremor.

We also conducted an active Airgun experiment at the second site to locate the conduit by tracking a pressure wave, using two arrays of surface seismic stations, as it propagated into the conduit. This combination of detecting and locating seismic microtremor generated by water flow in the conduits and the use of seismic array analysis to track active Airgun source pressure waves propagating at depth in conduits offers a new tool kit for karst hydrology determination. In the next step, we will assess the applicability of Distributed Acoustic Sensing (DAS) using fiber optic cables as sensors for detecting sub-surface water flow, where we expect unrivaled spatial resolution of the flow-induced seismic wavefield. Such a study would be the first attempt to fill the current gap regarding an understanding of karst groundwater dynamics along the entire conduit pathway, at an exceptionally high spatial scale.

How to cite: Karbala Ali, H., Bean, C. J., and Chalari, A.: Detection and source location of the groundwater-induced seismic signal in karst using a combination of passive and active seismic approaches, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1046, https://doi.org/10.5194/egusphere-egu23-1046, 2023.

10:05–10:15
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EGU23-5344
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Highlight
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On-site presentation
Jordi Diaz, Mario Ruiz, Mireia Udina, Francesc Polls, Davis Martí, and Joan Bech

Data acquired by a dense seismic network deployed in the Cerdanya basin (Eastern Pyrenees) is used to track the temporal and spatial evolution of meteorological events such as rainfall episodes or thunderstorms. Comparing seismic and meteorological data, we show that for frequencies above 40 Hz, the dominant source of seismic noise is rainfall and hence the amplitude of the seismic data can be used as a proxy of rainfall. The interstation distance of 1.5 km provides an unprecedented spatial resolution of the evolution of rainfall episodes along the basin. Two specific episodes, one dominated by stratiform rain and the second one dominated by convective rain, are analyzed in detail, using high resolution disdrometer data from a meteorological site near one of the seismic instruments.

Seismic amplitude variations follow a similar evolution to radar reflectivity values, but in some stratiform precipitation cases, it differs from the radar-derived precipitation estimates in this region of abrupt topography where radar may suffer antenna beam blockage. Hence, we demonstrate the added value of seismic data to complement other sources of information such as rain-gauge or weather radar observations to describe the evolution of ground-level rainfall fields at high spatial and temporal resolution. The seismic power and the rainfall intensity have and exponential relationship and the periods with larger seismic power are coincident. The time periods with rain drops diameters exceeding 3.5 mm do not result in increased seismic amplitudes, suggesting that there is a threshold value from which seismic data are no longer proportional to the size of the drops.

Thunderstorms can be identified by the recording of the sonic waves generated by thunders. We show that single thunders can be recorded to distances of a few tens of kilometers. As the propagation of these acoustic waves is expected to be strongly affected by parameters as air humidity, temperature variations or wind, the seismic data could provide an excellent tool to investigate atmospheric properties variations during thunderstorms.

How to cite: Diaz, J., Ruiz, M., Udina, M., Polls, F., Martí, D., and Bech, J.: Tracking storms in the Pyrenees using a dense seismic network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5344, https://doi.org/10.5194/egusphere-egu23-5344, 2023.

Coffee break
Chairpersons: Małgorzata Chmiel, Josefine Umlauft
Sediments and Rocks
10:45–10:55
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EGU23-7136
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ECS
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On-site presentation
Joachim Rimpot, Clément Hibert, Jean-Philippe Malet, Germain Forestier, and Jonathan Weber

In the context of climate change, the occurrence of geohazards such as landslides or rockfalls might increase. Therefore, it is important to have the ability to characterise their (spatial and temporal) occurrences in order to implement protection measures for the potential impacted populations and infrastructures. Nowadays, several methods including Machine Learning algorithms are used to study landslides-triggered micro-seismicity and the associated seismic sources (eg. rockfalls and  slopequakes). Those innovative algorithms allow the automation of the processing chains used to build micro-seismicity catalogues, leading to the understanding of the landslide deformation pattern and internal structure. Unfortunately, each landslide context has its own seismic signature which requires the use of the most complete and handmade training samples to train a Machine Learning algorithm. This is highly time consuming because it involves an expert that needs to manually check every seismic signal recorded by the seismic network, which can be thousands per day.

The aim of this study is to develop semi-supervised and unsupervised clustering methods to characterise the micro-seismicity of landslides in near real time. Here, we present the preliminary results obtained for creating a landslide micro-seismicity catalogue from the analysis of a dense network of 50 seismic stations deployed temporarily at the Super-Sauze landslide (French Alps). First, we present the performance of supervised Random Forest and XGBoost trained models on the event signals. Then, an approach aimed at processing streams of raw seismic data based on 18s-length windows is explored. Finally, we discuss the clustering results and the transferability possibilities of the approach to other landslides and even environments (glaciers, volcanoes).

How to cite: Rimpot, J., Hibert, C., Malet, J.-P., Forestier, G., and Weber, J.: Towards a generic clustering approach for building seismic catalogues from dense sensor networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7136, https://doi.org/10.5194/egusphere-egu23-7136, 2023.

10:55–11:05
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EGU23-3773
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ECS
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Virtual presentation
Wei Li, Dongpo Wang, and Zhen Zhang

Large rockfalls often cause huge economic losses and casualties in densely populated mountain areas. Timely acquiring information on a large rockfall can help promptly assess the damage and residual risks and guide the emergency response. Recent works suggest that the seismic signals generated by large rockfalls can provide these key information, but most of them focused on exploring seismic signatures to understand rockfall dynamics, lacking a rapid disaster assessing scheme. Here, we establish a seismic signal-based assessment scheme and demonstrate its capability by taking a large event – the 5 April 2021 Hongya rockfall (Sichuan, China) – as a case study. This scheme consists of three components, which are rockfall identification, detection and location, and characterization. In the rockfall identification module, we show how a rockfall can be distinguished from an earthquake and a rockslide by analyzing its seismic signatures. In the detection and location module, we demonstrate how the kurtosis-based method can be used to rapidly detect the initiation of a rockfall and determine the seismic wave velocity accordingly, and how the arrival-time-based location method can be used to locate a rockfall event. In the rockfall characterization module, we show how rockfall volume can be estimated from the magnitude of radiated seismic energy and how to characterize the dynamic process of a rockfall by the signatures of seismogram, spectrum and recorded seismic energy. Our results show that the seismic signal-based scheme presented here is suitable to characterize large rockfalls and has certain potential for rapid and effective emergency management.

How to cite: Li, W., Wang, D., and Zhang, Z.: Large rockfall detection, location and characterization using broadband seismic records: A case study of Hongya rockfall, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3773, https://doi.org/10.5194/egusphere-egu23-3773, 2023.

11:05–11:15
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EGU23-2707
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On-site presentation
Eric Larose, Antoine Guillemot, Laurent Baillet, and Pierre Bottelin

Rainfalls and freeze-thaw cycles are well known to largely contribute to rock slopes erosion, including chemical processes (dissolution, alteration) together with mechanical action (stress change in fractures due to water freezing). The role of heat waves and thermal cycles is less studied in dry conditions. Here we present a thermo-acousto-elastic (TAE) model for rock volumes exposed to cyclic (daily to seasonal) thermal forcings, as an application of environmental seismology (1).

In our model, we assume that the rock temperature is constant at depth (a few meters in general), and that the free surface is exposed to heat fluxes (radiative and convective ones). In practice, these heat fluxes can be respectively derived from solar radiation normal to the rock surface and from the air temperature, both parameters are easily measured in the field. We then develop a numerical model based on a) thermal diffusion (heat propagation in the rock in 2D or 3D models, including complex geometries as cracks, rock columns…), b) thermal expansion relating temperature to strain, and c) acousto-elasticity relating the elastic parameters to the state of stress, (2). Such a model is run, for example, with COMSOL Multiphysics with a finite element scheme. We end up with a 2D or 3D numerical model of stress and deformation of the rock volume evolving over time ranging from sub-daily to yearly time scales.

As an application we test this model on various rock columns and observe that the developed model properly reproduces field observations, including daily and seasonal cycles: the natural resonance frequency of the rock column, a proxy for its rigidity, increases with increasing heat flux (3) and the rear crack closes up. As a result of fitting our numerical model to natural rock columns, we can evaluate the acousto-elastic constant that relates the rigidity to the state of stress, a parameter that is known to mainly depend on the state of damage of the material, opening the route for rockfall risk assessment, monitoring and early warning systems. Our model also allows to shed new light into fatigue and cyclic damage process of rock slopes and cliffs, a key to rock erosion.

 

References:

  • (1) Guillemot, L. Baillet, E. Larose, P. Bottelin : Changes in resonance frequency of rock columns due to thermoelastic effects on a daily scale : observations, modeling and insights to improve monitoring, Geoph. J. Int. 231, 894-906 (2022).
  • (2) Larose, E. & Hall, S.: Monitoring stress related velocity variation in concrete with a 2.10−5 relative resolution using diffuse ultrasound, J. acoust. Soc. Am., 125, 1853–1856 (2009).
  • (3) Bottelin, P., Levy, C., Baillet, L., Jongmans, D. & Gueguen, P.: Modal and thermal analysis of Les Arches unstable rock column (Vercors massif, French Alps), Geophys. J. Int., 194, 849–858 (2013).

How to cite: Larose, E., Guillemot, A., Baillet, L., and Bottelin, P.: Thermo-Acousto-Elasticity (TAE) of natural rock cliffs: toward better understanding and monitoring damage and erosion process, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2707, https://doi.org/10.5194/egusphere-egu23-2707, 2023.

11:15–11:25
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EGU23-12687
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ECS
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On-site presentation
Thoralf Dietrich, Eva P.S. Eibl, Eyjólfur Magnússon, Daniel Binder, Sebastian Heimann, and Sigrid Roessner

Understanding the spatiotemporal details in the occurrence of jökulhlaups, also referred to as glacier lake outburst floods (GLOFs), is important for improving early warning and forecasting future events. Jökulhlaups occur in many different glacier-related settings and differ in their characteristics depending on the natural conditions: From very rapid floods (minutes-hours) originating from moraine dammed lakes in steep valleys to gradual floods (days-weeks) from subglacial lakes such as the ones beneath Vatnajökull ice cap, in Iceland. Previous studies of the October 2015 Skaftá jökulhlaup suggested that several hours of early-warning is possible based on the generated seismic tremor. Here, for the first time, we looked into all three spatial components of GNSS and seismic array data, respectively. Previous studies have already analysed the seismic events (icequakes, tremor, other migrating transient events) in detail, yet only on the z component. We reprocessed all three components of the seismic array data using frequency-wavenumber -analysis (fk-analysis) and match field processing (MFP). Both techniques allow to locate distant signal sources, either by direction only (fk) or actual location (MFP). We specifically focused on the time period when the tremor source is moving with the flood front and found two unexplained seismic signals:

  • A second migrating signal is visible on the lowermost part of the flood path 6 hours later than the passing of the first flood front.

    We compared this with a GNSS observations on top of the subglacial flood path and a hydrometric station 25 km downstream from the glacier margin in the affected Skaftá-river.

    After aligning the time series by the arrival of the pressure wave, the timing of the second seismic signal fits well with a 10 cm uplift of the glacier at the GNSS station; but also with a change in the rate of water level rise at the hydrometric station.

    We discuss this in the context of either explaining GNSS, hydrometric and seismological data individually or giving a hypothetical process that explains all three together. That could be a second intraglacial water lense draining, after the emptying of the lake deformed the overlaying glacier and connected the two water bodies. However, radio echo sounding survey over the source area in spring 2015 did not indicate a significant intraglacal water lense above the subglacial lake. The GNSS data may be cleared as noise artifact and the hydrometric data explained by flow of water out of the river course of Skaftá and onto porous lava fields between Sveinstindur, where the discharge of Skaftá is measured, and the glacier. Yet: The seismic signal then is left unexplained and open for discussion.

  • Finally, 18 hours after the first pulse, we found a sudden deceleration in horizontal motion on the GNSS that coincided with a sudden increase in seismic signals originating at the glacier terminus. We discuss if what we see is actually the glacier stopping, after losing the flood lubrication.

 

How to cite: Dietrich, T., Eibl, E. P. S., Magnússon, E., Binder, D., Heimann, S., and Roessner, S.: Surprising seismological signals during the October 2015 Skaftá jökulhlaup, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12687, https://doi.org/10.5194/egusphere-egu23-12687, 2023.

11:25–11:35
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EGU23-7727
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Virtual presentation
Susan Bilek, J. Mitchell McLaughlin, Daniel Cadol, and Jonathan Laronne

Use of seismic monitoring and data analysis techniques in recent years have allowed for improved understanding of several shallow earth processes, such as glacial motion, subsurface water flow, and bedload transport. Early applications using seismic data collected at high energy alpine rivers suggest that seismic energy within certain frequency bands is linked to bedload discharge.  However, study of other river systems have been more limited, even though some of these systems, such as ephemeral streams in arid environments, transport large quantities of sediment during short-lived flash flood events.  Here we present seismic and hydrologic data collected in a unique sediment observatory within an ephemeral tributary to the Rio Grande River, in the desert southwest of the U.S., combining dense seismic observations with a variety of in-channel bedload and water monitoring measurements. We have seismic records for more than a dozen floods ranging in depth from a few centimeters to over one meter, encompassing bedload flux as high as 12 kg s-1 m-1, two orders of magnitude higher than in most perennial settings. Our efforts to date focus on identifying the noise sources within the seismic record, characterization of the seismic properties of the site, and determining the seismic frequency ranges best correlated with the automatically measured bedload flux. Within the 30-80 Hz frequency range, we find a linear relationship between seismic power and bedload flux. We hypothesize that variations in linear fit statistics between flood events are due to varying bedload grain size distributions and in-channel morphological changes.

How to cite: Bilek, S., McLaughlin, J. M., Cadol, D., and Laronne, J.: Using Seismic Methods to Monitor Bedload Transport Along a Desert Environment Ephemeral Tributary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7727, https://doi.org/10.5194/egusphere-egu23-7727, 2023.

11:35–11:45
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EGU23-4500
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On-site presentation
Aurelien Mordret, Anais Lavoué, Benjamin Witten, Adam Baig, Sophie Beaupretre, Romeo Courbis, and Chloé Gradon

The collapse at depth of a cavern on the side of the Napoleonville salt dome, Assumption Parish, Louisiana, led to the formation of a large sinkhole at the surface. Besides surficial evidence from direct observations, the precise timeline of the evolution of the sinkhole is poorly known.  Here, we used two years of continuous ambient seismic vibrations recorded at 11 3-component seismic stations located around the Bayou Corne sinkhole to monitor the daily relative seismic velocity changes associated with the sinkhole activity. The sinkhole started to form in 2012 and had several phases of activity. The seismic network was installed in early 2013 and recorded the last major collapses before settling in 2014. Following standard seismic interferometry processing, we computed the full 9-component tensors of ambient vibrations cross-correlations between each pair of sensors. After a drastic quality check of the correlations, we rejected several components for which we did not have enough data or for which the data were corrupted in a way that was difficult to correct. We monitored the relative velocity variations (dv/v) during the studied period using the stretching method in the 0.9-3 Hz frequency band within the early coda of the correlations. We employed a reference-less inversion procedure to obtain a dv/v time series for each component and each pair of stations. The multi-component pairs curves are averaged to get the final time series. The results show significant velocity changes in early 2013 associated with the collapse phases of the sinkhole. The velocity recovers steadily after the second half of 2013 and all of 2014. Two seismically active periods generate smaller velocity drops. In agreement with the spatial extension of the sinkhole toward the southwest seen from the surface, the pairs of stations the most affected by large velocity drops are the ones located along the southwestern shore of the lake.
Our monitoring allows for refining the timeline of the events affecting the sinkhole and its overall activity with a daily temporal resolution. From the analysis of these two years of data, the sinkhole stabilized after intense activity in early 2013. The large velocity variations indicate a strong destructuring of the ground, with potential fracturing and water invasion.

How to cite: Mordret, A., Lavoué, A., Witten, B., Baig, A., Beaupretre, S., Courbis, R., and Gradon, C.: Ambient noise monitoring of the Bayou Corne sinkhole evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4500, https://doi.org/10.5194/egusphere-egu23-4500, 2023.

11:45–11:55
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EGU23-6264
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On-site presentation
Aurélie Martin, Thomas Lecocq, Ari Lannoy, Yves Quinif, Thierry Camelbeeck, and Nathalie Fagel

Karstic zones are numerous on Earth and offer a particular field of study to evaluate the ground motion levels that occurred in the past in support of regional seismic hazard assessment. Indeed, some fine and slender candlestick stalagmites are intact and therefore indicate that a certain level of ground motion has not been exceeded since they exist. Many parameters must be considered in the behaviour of stalagmites to earthquakes such as their shape, their mechanical properties and their natural frequency. A good way to better understand and characterize the reaction of these stalagmites to earthquakes is to study their reaction to the current permanent ground motion. To do this, a study based on the measurement of ambient seismic noise is underway in the cave of Han-sur-Lesse (Ardenne, Belgium). The ambient seismic noise is measured both at the surface (above the limestone massif and in the nearest village), on the floor of the cave and on the stalagmites themselves. Different three-component seismic sensors are used in parallel: three SmartSolo IGU-16HR 3C and two Raspberry Shake 3D Personal Seismographs, one of which has been adapted to be easily attached to the stalagmites. This parallel configuration during two-week recording periods made it possible to determine the eigenfrequencies and the polarization of the associated movements of 16 stalagmites. In addition, daily and weekly variations in ambient noise and transient events are measured such as earthquakes, quarry explosions or flooding in the cave. The presence of sensors in different places over the same period also makes it possible to study the possible impact of the cave's local characteristics on these measurements.

How to cite: Martin, A., Lecocq, T., Lannoy, A., Quinif, Y., Camelbeeck, T., and Fagel, N.: Stalagmites' reactions to ground motion studied using modified Raspberry Shake and nodal sensors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6264, https://doi.org/10.5194/egusphere-egu23-6264, 2023.

11:55–12:05
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EGU23-714
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ECS
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On-site presentation
Jonas Preine, Christian Hübscher, Jens Karstens, Gareth Crutchley, and Paraskevi Nomikou

Located in the southern Aegean Sea, the Christiana-Santorini-Kolumbo volcanic field is one of the most hazardous volcanic regions in the world and lies in an active continental rift zone. Northeast of Santorini lies the Kolumbo Volcanic Chain (KVC), which comprises more than 20 submarine volcanic cones, with the Kolumbo volcano representing the most prominent edifice of this chain. However, due to their inaccessibility, little is known about the spatio-temporal evolution and tectonic control of these submarine volcanoes and their link to the volcanic plumbing system of Santorini. We will present multichannel reflection seismic data that allow us to image the internal architecture of the KVC and study its link to Santorini. Using a seismostratigraphic framework, we are able to show the KVC evolved during two episodes, which initiated at approx. 1 Ma with the formation of mainly effusive volcanic edifices along a NE-SW trending zone. Most of the cones of the second episode represent submarine pumice cones that were formed by submarine explosive eruptions between 0.7 and 0.3 Ma and partly developed on top of volcanic edifices from the first episode. Our data show that two prominent normal faults underlie the KVC, indicating a direct link between tectonics and volcanism. In addition, we are able to reveal several buried volcanic centers and a distinct volcanic ridge connecting the KVC with Santorini, suggesting a connection between the two volcanic centers in the past. We argue that this connection was interrupted by a major tectonic event and, as a result, the two volcanic systems now have separate, largely independent plumbing systems despite their proximity.

How to cite: Preine, J., Hübscher, C., Karstens, J., Crutchley, G., and Nomikou, P.: Seismic imaging of the submarine Kolumbo Volcanic Chain reveals its volcano-tectonic evolution and link to Santorini, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-714, https://doi.org/10.5194/egusphere-egu23-714, 2023.

Posters on site: Mon, 24 Apr, 14:00–15:45 | Hall X3

Chairpersons: Josefine Umlauft, Michael Dietze, Małgorzata Chmiel
X3.1
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EGU23-900
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ECS
Ian Kelly, Anya Reading, Tobias Staal, and Andrew Bassom

The need to better predict how the great ice sheets will respond to continued atmospheric and ocean warming is paramount. Ice deformation and mechanisms for ice sliding across the bedrock underneath are both key considerations. Constraints of this critical ice-bedrock interface zone, particularly over extensive inland areas of Antarctica and Greenland, remain a major hurdle in ice-sheet modeling and estimations of future sea level rise.

Passive seismology offers a logistically-efficient avenue for such investigations, with improvements in sensor technologies, autonomous power solutions and telemetry systems encouraging the deployment of temporary arrays for subglacial mapping and real-time monitoring. Previous experiments have demonstrated the potential of techniques such as receiver functions, horizontal-to-vertical spectral ratios (HVSR) and ambient noise interferometry for characterising the depth and nature of the ice-bedrock zone. This research looks to fully explore the sensitivity range of available passive seismic methods for the ice-bedrock interface, with a view towards optimising data collection and array geometries for future applications. In this contribution, we present an optimised workflow making use of HVSR analysis and the spatial autocorrelation (SPAC) technique using numerical simulations and field data collected from East Antarctica. The results from this study provide a benchmark to guide future deployments in the polar regions.

How to cite: Kelly, I., Reading, A., Staal, T., and Bassom, A.: Optimising passive seismic investigations of the ice-bedrock interface zone for the great ice sheets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-900, https://doi.org/10.5194/egusphere-egu23-900, 2023.

X3.2
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EGU23-13334
Janneke van Ginkel, Fabian Walter, Ana Nap, Mauro Häusler, and Martin Lüthi

Climate change is causing major shifts in the dynamics of the cryosphere, leading to sea-level rise, glacier break-off events, flooding, and landslides. Geological, thermodynamic and hydraulic processes at the base of an ice mass play a central role in ice flow dynamics, and understanding these is imperative for predicting ice body behavior in a changing climate. To this end, sustained ambient vibrations in glaciated environments can be used to monitor subglacial conditions over significant spatial extent with relatively low-cost acquisition.

In earthquake seismology, a well-established methodology to investigate subsurface properties is the horizontal-to-vertical spectral ratio (H/V) of ambient seismic ground unrest. In cryoseismology, the H/V approach is already used to invert for velocity profiles of ice or firn, to obtain bedrock topography and to identify the presence of basal sediments. To date, only a few hours of seismic vibration records are typically used. Yet in such short time records, biases may arise because of the dynamic character of the glacier. Seismic resonances within the soft ice layer and resulting H/V ratios are expected to vary with changes in subglacial hydraulic conditions.

We propose to leverage temporal variations in H/V spectra to investigate subglacial processes. As a case study, we first focus on the Glacier de la Plaine Morte (Switzerland), where a seismic array was deployed for four months in summer of 2016. During this time, an ice-marginal lake formed and suddenly drained through and under the glacier, making this seismic record ideal for our purposes. This drainage event is well recorded and strongly influences the H/V in terms of amplitude and resonance frequency. We next present ambient H/V measurements of the Sermeq Kujalleq in Kangia (also known as Jakobshavn Isbræ), one of Greenland’s largest outlet glaciers. Here, the H/V spectra show multiple resonances over time, whose origin we discuss in more detail. For both our study cases, separating variations in source and medium properties is pivotal. Tackling this challenge provides glaciologists with a valuable tool to investigate the poorly accessible subglacial environment, which holds the key to our understanding of ice flow and eustatic sea level rise.

How to cite: van Ginkel, J., Walter, F., Nap, A., Häusler, M., and Lüthi, M.: Ambient H/V sensitivity to the dynamics of glaciers and ice sheets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13334, https://doi.org/10.5194/egusphere-egu23-13334, 2023.

X3.3
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EGU23-7489
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ECS
Tifenn Le Bris, Guilhem Barruol, Emmanuel Le Meur, Florent Gimbert, and Dimitri Zigone

In coastal Antarctica, outlet glaciers exhibit complex dynamics materialized by intense internal deformation, enhanced basal sliding and strong thermo-mechanical interactions with the ocean. Here we aim to use seismic observations to unravel these various processes and their link with glacier and ocean dynamics. As part of the SEIS-ADELICE project (2020-2024) supported by the French Polar Institute IPEV, in January 2022 we deployed four permanent and six temporary (1 month long) broadband seismic stations on and around the Astrolabe Glacier (Terre Adélie, East Antarctica), as well as four ocean-bottom seismometers at sea near the terminus of the floating tongue. In January 2023 we will be supplementing this setup by a temporary network of 50 seismic nodes above the grounding line of the glacier.

Preliminary detection and classification of seismic events reveals a wide variety of cryo-seismic signals. The most pervasive events correspond to icequakes, are located close to the surface, and exhibit clear tidal modulation. We interpret these events as being generated by the brittle fracturing of ice associated with crevasse opening. We also observe numerous short and similar repetitive events of much lower amplitude that are located at few restricted locations near the ice-bedrock interface. These events are likely produced by basal stick-slip over punctual bedrock asperities. Finally, we observe glacial tremors which could result from hydraulic sources at the ice-bedrock interface, although further analysis is required to confirm this hypothesis.

This preliminary work provides useful grounds for deeper analysis to be done in the future on source characteristics and their more quantitative links with glacier dynamics.

How to cite: Le Bris, T., Barruol, G., Le Meur, E., Gimbert, F., and Zigone, D.: Monitoring the cryoseismic activity of the Astrolabe glacier, Terre Adélie, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7489, https://doi.org/10.5194/egusphere-egu23-7489, 2023.

X3.4
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EGU23-13269
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ECS
Johanna Zitt, Patrick Paitz, Fabian Walter, and Josefine Umlauft

One major challenge in Environmental Seismology is that signals of interest are often buried within the high noise level emitted by a multitude of environmental processes. Those signals potentially stay unnoticed and thus, might not be analyzed further.

Distributed acoustic sensing (DAS) is an emerging technology for measuring strain rate data by using common fiber-optic cables in combination with an interrogation unit. This technology enables researchers to acquire seismic monitoring data on poorly accessible terrain with great spatial and temporal resolution. We utilized a DAS unit in a cryospheric environment on a temperate glacier. The data collection took place in July 2020 on Rhonegletscher, Switzerland, where a 9 km long fiber-optic cable was installed, covering the entire glacier from its accumulation to its ablation zone. During one month 17 TB of data were acquired. Due to the highly active and dynamic cryospheric environment, our collected DAS data are characterized by a low signal to noise ratio compared to classical point sensors. Therefore, new techniques are required to denoise the data efficiently and to unmask the signals of interest. 

Here we propose an autoencoder, which is a deep neural network, as a denoising tool for the analysis of our cryospheric seismic data. An autoencoder can potentially separate the incoherent noise (such as wind or water flow) from the temporally and spatially coherent signals of interest (e.g., stick-slip event or crevasse formation). We test this approach on the continuous microseismic Rhonegletscher DAS records. To investigate the autoencoder’s general suitability and performance, three different types of training data are tested: purely synthetic data, original data from on-site seismometers, and original data from the DAS recordings themselves. Finally, suitability, performance as well as advantages and disadvantages of the different types of training data are discussed.

How to cite: Zitt, J., Paitz, P., Walter, F., and Umlauft, J.: Denoising Cryoseismological Distributed Acoustic Sensing Data Using a Deep Neural Network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13269, https://doi.org/10.5194/egusphere-egu23-13269, 2023.

X3.5
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EGU23-6300
Patrick Paitz, Małgorzata Chmiel, Lena Husmann, Michele Volpi, Francois Kamper, and Fabian Walter

Hazardous mass-movements pose a great danger to the population and critical infrastructure, especially in alpine areas. Monitoring and early-warning systems can potentially save many lives and improve the resilience of mountain communities to catastrophic events. Increasing coverage of seismic networks recording hazardous mass-movements opens up new warning perspectives as long as efficient algorithms screening the seismic data streams in real-time are available.

We propose to combine physical and statistical properties of seismic ground velocity recordings from geophones and seismometers as a foundation for an unsupervised workflow for mass movement detection. We evaluate the performance, consistency, and generalizability of unsupervised clustering algorithms like K-means and Bayesian Gaussian Mixture Models against supervised methods like the Random Forest classifier. Focusing on debris-flow records at the Illgraben torrent in Switzerland, we present a generic mass-movement detector with high accuracy and early-warning capability. We apply this detector to other datasets form other sites to investigate its transferability.

Since our results aim to enable mass-movement monitoring and early-warning worldwide, Open Research Data principles like Findability, Accessibility, Interoperability and Reusability (FAIR) are of high importance for this project. We discuss how using the Renku (renkulab.io) platform of the Swiss Data Science Center ensures FAIR data science principles in our investigation. This is a key step towards our ultimate goal to enable seismology-based early warning of mass-movements wherever it may be required.

How to cite: Paitz, P., Chmiel, M., Husmann, L., Volpi, M., Kamper, F., and Walter, F.: Towards an unsupervised generic seismic detector for hazardous mass-movements: a data-driven approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6300, https://doi.org/10.5194/egusphere-egu23-6300, 2023.

X3.6
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EGU23-8986
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ECS
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Tjeerd Kiers, Cédric Schmelzbach, Pascal Edme, Patrick Paitz, Florian Amann, Hansruedi Maurer, and Johan Robertsson

Landslides are a major natural hazard that can cause significant loss of life and property damage around the world. As global temperatures rise and weather extremes become more frequent, we can expect an increase in the hazard emanating from landslides too. In order to better understand and mitigate landslide risks, a variety of strategies have been developed to characterize and monitor landslide activity. Many established approaches provide valuable information about surface displacement and surface properties, but are not suited to inspect the subsurface parts of a landslide body. In contrast, seismic imaging and monitoring methods allow us to study subsurface structures, properties, and internal processes that control landslide behaviour.

In our project, we develop novel seismic data acquisition and interpretation approaches to characterize and monitor one of the largest active unstable slopes in the Alps, the Cuolm da Vi landslide, with an unprecedented spatial resolution. We achieve this by combining an array of over 1’000 seismic nodes with fiber-optic based monitoring techniques such as Distributed Acoustic (DAS) and Strain Sensing (DSS).

The deep-seated Cuolm da Vi landslide is located near Sedrun (Central Switzerland) and consists of approximately 100-200 million m3 of unstable rock reaching displacement rates up to 10-20 cm/yr with clear seasonal cycles. In summer 2022, we buried over 6 kilometres of fiber-optic cable in this alpine environment covering the most active part of the landslide with multiple cable orientations. Additionally, we deployed a nodal array of 1046 accelerometers in a hexagonal grid covering around 1km2 with a nominal spacing of 28 meters. Seismic data were acquired with the nodes and the DAS system continuously for four weeks. This time period included the blasting of 163 dynamite shots for calibration and active-source imaging purposes. In 2023, we plan to conduct data acquisition for longer periods using primarily fibre-optic based techniques with a focus on the temporal evolution of the landslide dynamics.

Our first goal is to resolve the internal structure of the landslide based on the controlled-source data acquired in summer 2022 to construct, for example, a seismic velocity model. Based on the models derived from the active-source seismic data, we plan to exploit the continuous seismic recordings of ambient vibrations and potential seismic signals produced by the landslide activity to complement structural models and study the landslide dynamics. We will present our current results and discuss their implications for the next steps towards monitoring this landslide over time.

How to cite: Kiers, T., Schmelzbach, C., Edme, P., Paitz, P., Amann, F., Maurer, H., and Robertsson, J.: Monitoring of an Alpine landslide using dense seismic observations: combining Distributed Acoustic Sensing and 1000 autonomous seismic nodes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8986, https://doi.org/10.5194/egusphere-egu23-8986, 2023.

X3.7
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EGU23-8127
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ECS
Qi Zhou, Hui Tang, Jens M. Turowski, Jean Braun, Michael Dietze, Fabian Walter, Ci-Jian Yang, Sophie Lagarde, and Ahmed Abdelwahab

Rapid mass movements are a major threat in populated landscapes, as they can cause significant loss of life and damage civil infrastructure. Previous work has shown that using environmental seismology methods to monitor such mass movements and establish monitoring systems offers advantages over existing approaches. The first important step in developing an early warning system for rapid mass movements based on seismic signals is automatically detecting events of interest. Though the approach, such as short-term average to long-term average ratio (STA/LTA) and machine learning model, was introduced to detect events (e.g., debris flow and rockfall), it is still challenging to calibrate input parameters and migrate existing methods to other catchments. Detection of debris flows, for instance, is similar to anomaly detection if we consider the seismic stations recording background signals as an overwhelming majority condition. 
Benford's law describes the probability distribution of the first non-zero digits in numerical datasets, which provides a functional, computationally cheap approach to anomaly detection, such as fraud detection in financial data or earthquake detection in seismic signals. In this study, seismic signals generated by rapid mass movements were collected to check the agreement of the distribution of the first digit with Benford's law. Subsequently, we develop a computationally efficient and non-site-specific model to detect events based on Benford's law using debris flows from the Illgraben, a Swiss torrent, as an example. Our results show that seismic signals generated by high-energy mass movements, such as debris flows, landslides, and lahars, follow Benford's law, while those generated by rockfall and background signals do not. Furthermore, our detector performance in picking debris-flow events is comparable to a published random forest and seismic network-based approach. Our method can be applied at other sites to detect debris-flow events without additional calibration and offers the potential for real-time warnings.

How to cite: Zhou, Q., Tang, H., Turowski, J. M., Braun, J., Dietze, M., Walter, F., Yang, C.-J., Lagarde, S., and Abdelwahab, A.: Benford's law in detecting rapid mass movements with seismic signals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8127, https://doi.org/10.5194/egusphere-egu23-8127, 2023.

X3.8
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EGU23-6049
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ECS
Charlotte Bruland, Andreas Köhler, and Volker Oye

Historically, there is one larger quick clay landslide in Norway every year. Since 80 percent of those happen in known quick clay risk areas, it is important to monitor these sites continuously. Alna, a busy, urban area in Oslo, is an example of such a location where a quick clay slide could lead to substantial human and economical losses.

In this study we use ambient noise methods to monitor changes in the subsurface at Alna using a small array of three-component seismic sensors. To retrieve small velocity changes, we apply coda wave interferometry using 12 months of urban seismic noise (above 1 Hz).

We compare the observed day-to-day changes to air temperature, precipitation, and water levels in a nearby river, and observe environmental velocity fluctuations well correlated with air temperature and precipitation. In particular, freezing and thawing produces strong changes in seismic velocity (up to 4 percent). The surface wave-coda used here is sensitive to changes in shear wave velocity, which in turn can be used to detect changes of the sub-surface properties. Therefore, observed velocity variations at Alna could have potential for monitoring and early warning of quick clay instabilities.

How to cite: Bruland, C., Köhler, A., and Oye, V.: Towards quick clay monitoring in the city of Oslo, Norway with urban seismic noise, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6049, https://doi.org/10.5194/egusphere-egu23-6049, 2023.

X3.9
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EGU23-11404
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ECS
Davide Mancini, Michael Dietze, Tom Müller, Matthew Jenkin, Floreana Marie Miesen, Matteo Roncoroni, Andrew Nicholas, and Stuart Nicholas Lane

Alpine glaciers have been rapidly retreating and at increasing rates in recent decades due to climate warming. As a consequence, large amounts of suspended- and bed-load flux are being released to proglacial environments, such as proglacial forefields. These regions are among the most unstable geomorphic systems of the Earth because they rapidly respond to changing discharge and sediment conditions. Given this, it might be hypothesized that their intense morphodynamic activity, being a complex and non-linear process, could “shred” the sediment transport signal itself, and especially that related to subglacial sediment export.

To date, our knowledge on subglacial sediment export by subglacial streams is essentially dominated by suspended sediment dynamics recorded in front of shrinking glaciers because of the limitations in measuring bedload transport. The latter is usually monitored far downstream from glacier termini by permanent stations (e.g. water intakes, geophone systems) leaving major uncertainties in the absolute amounts and temporal patterns of transport in both glacial and proglacial environments, as well as the relative importance compared to suspended sediment in case of morphodynamic filtering. Thus, the aim of this project was to investigate the evolution of the both suspended- and bedload subglacial export signals within the proglacial forefield to quantify the extent and the timescale over which proglacial morphodynamics filter them.

This work focuses on a large Alpine glacial forefield, almost 2 km in length, that has formed since the early 1980s at the Glacier d’Otemma (southern-western Swiss Alps, Valais). Data were collected over two entire melt seasons (June-September 2020 and 2021) experiencing different climatic conditions, the first year warm and relatively dry and the second cold and relatively wet. Suspended transport was recorded using conventional turbidity-suspended sediment concentration relationship, bedload transport was monitored seismically, while the morphodynamic filtering was determined using signal post-processing techniques. At present, there are no studies combining continuous measurements of both suspended- and bed-loads in such environments.

Results show that the signal of subglacial bedload export, unlike suspended load export, is rapidly shredded by proglacial stream morphodynamics, which we show is due to a particle-size dependent autogenic sorting of sediment transport at both daily and seasonal time-scales. The result is that over very short distances, the signal of subglacial bedload sediment export is lost and replaced by a signal dominated by morphodynamic reworking of the proglacial braidplain. The suspended signal is less impeded but significant floodplain storage and release of suspended sediment was observed. These results question the reliability of current inferences of glacial erosion rates from sediment transport rates often measured some way downstream of glacier margins.

How to cite: Mancini, D., Dietze, M., Müller, T., Jenkin, M., Miesen, F. M., Roncoroni, M., Nicholas, A., and Lane, S. N.: Rapid shredding of the subglacial sediment export signal by proglacial forefields, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11404, https://doi.org/10.5194/egusphere-egu23-11404, 2023.

X3.10
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EGU23-13383
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ECS
|
Marjolein Gevers, Davide Mancini, Stuart Lane, and Ian Delaney

Increased glacier melt leads to a change in sediment transport capacity below glaciers, which impacts the sediment transport within proglacial areas as well as downstream ecosystems and geomorphology. Previous work on Alpine glaciers shows that strong diurnal discharge variations lead to fluctuations in sediment transport capacity such that deposition and erosion can occur in the proglacial area over the course of the melt season. However, the exact processes controlling sediment transport at the outlet glaciers of ice sheet margins and in their proglacial areas remain uncertain. Data suggest that the diurnal discharge variations are substantially reduced and baseflow discharge is much greater, likely capable of maintaining significant sediment transport throughout the melt season. This difference in the hydrological regime as compared with Alpine glacial systems may drive different rates and variations in sediment transport and, ultimately, in proglacial braid plain morphodynamics.

We measure proglacial sediment transport at Leverett glacier, a land-terminating glacier located at the western margin of the Greenland Ice Sheet. As bedload transport is exceptionally difficult to measure in situ, two seismic stations were installed to evaluate bedload transport in the glacial meltwater stream in the summer of 2022. The first station is located close to the current glacier terminus, and the second one is about 2 km from the current glacier terminus. These two stations allow for the examination of the sediment transport processes within the proglacial area. By using a Fluvial Inversion Model the recorded seismic data is converted into bedload flux. The model is calibrated using active seismic surveys and statistical approaches to evaluate the physical parameters. Outputs of the Fluvial Inversion Model are validated with available water stage data.  The results provide insight as to whether the proglacial area is aggrading or eroding as sediment transport in the two locations at Leverett glacier evolves over the summer season. We discuss the relationship between bedload transport and level of the proglacial river, as well as the seasonal variations in proglacial sediment transport and deposition in Leverett glacier’s proglacial area.

How to cite: Gevers, M., Mancini, D., Lane, S., and Delaney, I.: Using a record of bedload transport from Leverett glacier in western Greenland to understand proglacial sediment transport processes from the ice sheet  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13383, https://doi.org/10.5194/egusphere-egu23-13383, 2023.

X3.11
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EGU23-12128
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Chao Ting Meng, Wei An Chao, and Yu Shiu Chen

Monitoring temporal and spatial changes in sediment volume in the upstream reservoir is one of the important indicators for evaluating the reservoir project life, especially the information carried by bedload and suspended load. According to field condition, direct bedload monitoring is often difficult. Thus, bedload usually can be estimated by a specific proportion of suspended load depended on the flooding magnitude, which can cause a large uncertainty in estimates of total sediment load. In recent years, riverine micro-seismic signals have been applied to study bedload transport. Our study chose the Da-Pu Dam (location: 23.296500°N, 120.644611°E), located at the upstream of the Zeng-Wen Reservoir and the junction of the Zeng-Wen river and Cao-Lan river, which is the last check dam before entering the reservoir area. Its upstream catchment area is 30,312 hectares that comprise approximately 63% of the Zeng-Wen Reservoir catchment area (48,100 hectares). The length of the monitoring section of the Da Pu Dam is 1,100 meters, with an average width of 121 meters and an average slope of 0.36 degrees. With the available data composed of riverbed cross-section survey, sediment particle size distribution, fluvial measurements (water depth, surface flow velocity), orthoimagery, and suspended load measurement, our study applies seismic saltation model to estimate the bedload flux and compares the results with the measured suspended load. Results showed that there are different ratios between bedload and suspended load under similar hydrological condition during the plum rain season(May-June) and typhoon period(July-September). In a case of flooding event considering the flow stage from medium to high discharge, significant temporal changes in the ratio between bedload and suspended load can also be observed, which imply a complex transition process between the bedload and suspension particles. The temporal changes in sediment ratio obtained in this study can be applied to estimate the total volume of sediment load entering the reservoir. Our estimated results are consistent with the survey of sediment accumulation at the end of each year in the reservoir area.

How to cite: Meng, C. T., Chao, W. A., and Chen, Y. S.: Probing temporal variation of suspended load to bedload ratio using seismic saltation model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12128, https://doi.org/10.5194/egusphere-egu23-12128, 2023.

X3.12
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EGU23-3010
Su Young Kang, Kwang-Hee Kim, Doyoung Kim, Byungmin Kim, Lanbo Liu, and Youngcheol Lee

Many deep faults do not reach the earth’s surface and thus are not recognized. Such faults are rarely mapped by standard surface geological mapping. This seriously hinders seismic risk mitigation efforts. In this study, we applied the horizontal-to-vertical spectral ratio (HVSR) method to identify blind faults invisible at the surface. Despite its simplicity and low-cost implementation, we noticed that HVSR results were unstable using data collected by exposed seismometers or under higher wind speeds. Therefore, three-component seismic sensors for ambient noise observations were buried at different depths to examine the effects of ground coupling, wind speeds, and precipitations. Results from a series of field tests under diverse conditions guided us to establish data selection criteria. The first required condition is that seismic sensors should be buried (>0.3 meters) to secure ground coupling and to avoid any direct exposure to wind or precipitations. The other is that data should be collected at low wind speeds (< 3 m/s). The requirements were applied to ambient noise data along two profiles traversing unnamed and inferred faults in Pohang, Korea. We initially estimated the resonance frequencies for each site, which varied from 0.41 to 2.52 Hz. They were then converted to bedrock depths using an empirical relationship between the resonance frequency and depth to bedrock observed at boreholes in the area. The estimated depths to bedrock along profiles ranged from 8.0 to -472.0 meters. The resulting depth profiles show significant lateral variations in the bedrock depth, including the one near the Gokgang fault at which the thickness to the major impedance contrasts decreased from 196 to 20 meters. Sudden variations were also observed at unexpected locations along the profile. We examined the details, especially for sites of apparent changes in bedrock depth, and compared their characteristics with other geophysical studies, including Vs30, MASW, Bouguer gravity anomaly, and adjacent stations correlation. Their results are all well correlated to each other and indicate rapid changes in bedrock depth. We attribute the rapid changes to vertical displacements by ancient faulting activity.

How to cite: Kang, S. Y., Kim, K.-H., Kim, D., Kim, B., Liu, L., and Lee, Y.: Identification of bedrock depth and blind fault by HVSR analysis along two profiles in Pohang, South Korea considering optimal weather environment and seismometer burial depth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3010, https://doi.org/10.5194/egusphere-egu23-3010, 2023.

X3.13
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EGU23-7549
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ECS
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Highlight
Megan Baker, Peter Talling, Richard Burnett, Ed Pope, Sean Ruffell, Matthieu Cartigny, Michael Dietze, Morelia Urlaub, Michael Clare, Jeffrey Neasham, Ricardo Silva Jacinto, Pascal Kunath, and Christine Peirce

Seafloor sediment flows (turbidity currents) form some of the largest sediment accumulations on Earth, carry globally significant volumes of organic carbon, and can damage critical seafloor infrastructure. These fast and destructive events are notoriously challenging to measure in action, as they often damage any instruments anchored within the flow. We present the first direct evidence that turbidity currents generate seismic signals which can be remotely sensed (~1-3 km away), revealing the internal structure and remarkably prolonged duration of the longest runout sediment flows on Earth. Passive Ocean Bottom Seismograph (OBS) sensors, located on terraces of the Congo Canyon, offshore West Africa, recorded thirteen turbidity currents over an 8-month period. The occurrence and timing of these turbidity currents was confirmed by nearby moorings with acoustic Doppler current profilers.

Results show that turbidity currents travelling over ~1.5 m/s produce a seismic signal concentrated below 10 Hz with a sudden onset and more gentle decay. Comparison of the seismic signals with information on flow velocities from the acoustic Doppler current profilers demonstrates that the seismic signal is generated by the fast-moving front of the flow (frontal cell), which contains higher sediment concentrations compared to the slower-moving body. Long runout flows travelling >1000 km have a fast (3.7-7.6 m s-1) frontal cell, which can be 14 hours, and ~350 km long, with individual flows lasting >3 weeks. Flows travelling >1000 km eroded >1300 Mt of sediment in one year, yet had near-constant front speeds, contrary to past theory. The seismic dataset allows us to propose a fundamental new model for how turbidity currents self-sustain, where sediment fluxes into and from a dense frontal layer are near-balanced.

Seismic monitoring of turbidity currents provides a new method to record these hazardous submarine flows, safely, over large areas, continuously for years yet at sub-second temporal resolution. Monitoring these processes from land would considerably ease deployment efforts and costs. Thus, work is underway investigating if terrestrial seismic stations can record submarine seafloor processes in Bute Inlet, a fjord in western Canada where independent measurement of delta-lip failures and turbidity currents can be compared to a passive seismic dataset.

How to cite: Baker, M., Talling, P., Burnett, R., Pope, E., Ruffell, S., Cartigny, M., Dietze, M., Urlaub, M., Clare, M., Neasham, J., Silva Jacinto, R., Kunath, P., and Peirce, C.: Seabed seismometers reveal duration and structure of longest runout sediment flows on Earth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7549, https://doi.org/10.5194/egusphere-egu23-7549, 2023.

X3.14
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EGU23-3593
Michael Dietze, Christian Mohr, Violeta A. Tolorza, Benjamin Sotomayor, and Erwin Gonzalez

Weather conditions are an important driver of Earth surface dynamics, such as gravitational mass wasting, flood propagation, biological activity events and physical interactions within the critical zone. While there are dedicated sensors to capture meteorological parameters, these sensors are comparably expensive, have a small spatial footprint and often lack the temporal resolution needed to constrain high frequency meteorological dynamics. We introduce the concept of meteo-seismology, i.e. the measurement of first-order ground motion signatures of weather conditions by decisively installed seismic sensors. While meteorological manifestations are generally considered seismic noise and it may seem odd to use seismometers instead of weather stations, geophysical sensors circumvent or complement the above caveats and add further important data to a comprehensive picture of the rapidly changing state of the atmosphere and its interaction with the landscape we live in. Based on examples from prototype forested landscapes in Central Europe and Chilean Patagonia, we demonstrate how seismic stations can be used to infer properties of the pressure and wind field and its coupling to the biosphere, constrain rain intensity and drop properties, yield temperature proxies and their propagation into the ground, and survey ground moisture trends and discharge patterns. Understanding the seismic signatures of a meteorological origin also allows to, vice versa, better handle the contaminating side of these seismic sources in records, where high frequency signals are to be used for other than meteo-seismological studies. Our approach offers an alternative and complementary way to non-invasively monitor hydrometeorological energy and matter fluxes at high temporal and spatial resolution.

How to cite: Dietze, M., Mohr, C., Tolorza, V. A., Sotomayor, B., and Gonzalez, E.: Meteo-Seismology: Harvesting the Seismic Signals of Weather Dynamics in the Critical Zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3593, https://doi.org/10.5194/egusphere-egu23-3593, 2023.

X3.15
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EGU23-6321
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ECS
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Richard Kramer, Yang Lu, and Götz Bokelmann

In this study, we used coda wave interferometry to investigate four years of continuous data from AlpArray and other locations throughout Europe. We estimate the hourly Green’s function by cross-correlating ambient seismic noise recorded at pairs of stations. The results indicate short and long-term variations of the seismic velocities and show the feasibility of large-scale monitoring with ambient seismic noise at high temporal resolution. The relative seismic velocities (dv/v) show temporal variations on the order of 10-3 in a frequency band around 1 Hz. Spectra of the velocity time series contain strong daily and sub-daily behaviour, which are primarily caused by the coupling of atmospheric processes and solid Earth. The explanatory model focuses on depth variations of the groundwater table, linking atmospheric pressure (loading and unloading the Earth's surface) to variations in seismic velocity. This study aims to understand and explain differences in daily and sub-daily behaviour across Europe. This may contribute to the hydrological characterization of the near-subsurface in central Europe. 

How to cite: Kramer, R., Lu, Y., and Bokelmann, G.: Can we characterize groundwater reservoirs in central Europe from air-pressure-induced seismic velocity changes?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6321, https://doi.org/10.5194/egusphere-egu23-6321, 2023.

X3.16
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EGU23-675
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ECS
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Antonia Kiel, René Steinmann, Eric Larose, and Céline Hadziioannou

Nowadays, the majority of detailed information about groundwater is acquired by wells that provide limited insight in time and especially space. Therefore, it would be interesting to monitor groundwater by continuously measuring seismic velocity changes in the subsurface. The shallow soil is affected by environmental influences like temperature, rainfall or drought, which in turn changes the seismic velocity in the subsurface.

In this study, we use three-component seismometers, which are placed next to an in-situ measurement station of soil conditions (moisture and temperature at different depths) and a meteorological station in the city of Hamburg, Germany. We investigate the sensitivity of high-frequency (> 1 Hz) seismic waves with an anthropogenic origin to ground moisture changes in the uppermost layers of soil. To monitor velocity changes, Passive Image Interferometry is applied. Using the three-component data, we are able to retrieve Rayleigh and Love waves. Relative velocity changes are retrieved using the stretching method. A comparison of seasonal seismic velocity changes and environmental changes shows a positive correlation between velocity and temperature, as well as a negative correlation between velocity and groundwater content. Freezing events are exceptions, as they cause relative velocity increases twice as high as seasonal changes.

The aim of this work is to eliminate temperature effects to work towards inferring water content directly from seismic velocity changes. To eliminate the contribution of temperature, its relation to seismic velocity changes and water content is quantified using regression. Since the relative velocity change is influenced by both temperature and water content, a time period of stable water content is used to quantify the relation between velocity change and temperature. As a result, the residual relative velocity change reproduces the residual water content.

How to cite: Kiel, A., Steinmann, R., Larose, E., and Hadziioannou, C.: Can we monitor shallow groundwater using ambient seismic noise?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-675, https://doi.org/10.5194/egusphere-egu23-675, 2023.

Posters virtual: Mon, 24 Apr, 14:00–15:45 | vHall SSP/GM

Chairpersons: Josefine Umlauft, Michael Dietze, Małgorzata Chmiel
vSG.1
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EGU23-1677
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ECS
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Ian Lee, Sridhar Anandakrishnan, Richard Alley, Alex Brisbourne, and Andrew Smith

Basal icequakes are generated as a glacier slides over its underlying bedrock, and the stick-slip motion of constant loading and unloading releases shear stresses that produce these very small magnitude (ML < 0) glacial microseisms. Detecting and locating nucleation of these fine-scale icequakes can provide highly useful insights into the deformation processes occurring at the bed and consequently the mechanisms governing glacier flow. We present icequake data derived from a seismic array installed at the grounding line of the Rutford Ice Stream in West Antarctica by Penn State University and the British Antarctic Survey during the 2018/19 austral summer. The region’s natural source seismicity was first processed using the earthquake detection and location software QuakeMigrate and the events were relatively relocated using HypoDD/GrowClust. We then clustered the events into sticky spot clusters using the unsupervised clustering algorithm DBSCAN, and finally from the clusters we selected “model” waveforms to perform template matching on the original seismic traces to create methodically comprehensive high-resolution icequake catalogs at the grounding line of Rutford. We present our methodology including the complete processing pipeline (supplemented by developed supporting open-source scripts) along with key tuning parameters, and describe how our catalogs were used to resolve glacier sliding patterns and key topographical features and characteristics of the bed like sticky spots. We additionally explore the effects of tidal modulation and Rutford ice flow motion on icequake occurrences. Our seismic traces primarily contain icequake signals that derive from stick-slip sliding, but also unique waveforms that might be derived from crevassing and teleseisms that we will also explore. Our results show that stick-slip basal icequakes and these resultant icequake catalogs are valuable data-rich resources that help improve our understanding of glacier flow dynamics and will be important toward improving glacier flow models used for constraining global mean sea level rise.

How to cite: Lee, I., Anandakrishnan, S., Alley, R., Brisbourne, A., and Smith, A.: Event Relations and Sources of Icequakes at the Grounding Line of Rutford Ice Stream, West Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1677, https://doi.org/10.5194/egusphere-egu23-1677, 2023.