EnKF estimation of the viscoelastic deformation and the viscosity

2020 ◽  
Author(s):  
Makiko Ohtani
Keyword(s):  
Data Assimilation ◽  
Crustal Deformation ◽  
Surface Deformation ◽  
Synthetic Data ◽  
Ground Surface ◽  
Inelastic Strain ◽  
Large Earthquake ◽  
Forward Model ◽  
Viscoelastic Deformation ◽  
Large Earthquakes

<p>Following large earthquakes, postseismic crustal deformations are often observed for more than years. They include the afterslip and the viscoelastic deformation of the crust and the upper mantle, activated by the coseismic stress change. The viscoelastic deformation gives the stress change on the neighboring faults, hence affects the seismic activity of the surrounding area, for a long period after the large earthquake. So, estimating the viscoelastic deformation after the large earthquakes is important.</p><p>In order to estimate the time evolution of the viscoelastic deformation after a large earthquake, we also need to know the viscoelastic structure around the area. Recently, the Ensemble Kalman filter method (EnKF), a sequential data assimilation method, starts to be used for the crustal deformation data to estimate the physical variables (van Dinther et al., 2019, Hirahara and Nishikiori, 2019). With data assimilation, we get a more provable estimation by combining the data and the time-forward model than only using the data. Hirahara and Nishikiori (2019) used synthetic data and showed that EnKF could effectively estimate the frictional parameters on the SSE (slow slip event) fault, addition to the slip velocity. In the present study, I applied EnKF to estimate the viscosity and the inelastic strain after a large earthquake, both the physical property and the variables.</p><p>First, I constructed the forward model simulating the evolution of the viscoelastic deformation, following the equivalent body force method (Barbot and Fialko, 2010; Barbot et al., 2017). This method is appropriate for applying EnKF, because the ground surface deformation rate is represented by the inelastic strain at the moment, and the history of the strain is not required. Then, we applied EnKF based on the forward model and executed some numerical experiments using a synthetic postseismic crustal deformation data.</p><p>In this presentation, I show the result of a simple setting. I assumed the medium to be two layers with a homogeneous viscoelastic region underlying an elastic region. The synthetic data is made by giving a slip on a fault at time <em>t</em> = 0 and simulating the time evolution of the ground surface deformation. For assimilation, I assumed that the slip on the fault and the stress distribution just after the large earthquake is known. Then we executed the assimilation every 30 days after the large earthquake. I found that I can get a good estimation of the viscosity after <em>t</em> > 150 days.</p>

Stress-forecasting: a viable alternative to earthquake prediction in a dynamic Earth

1998 ◽  
Vol 89 (2) ◽  
pp. 121-133 ◽  
Author(s):  
Stuart Crampin
Keyword(s):  
Earthquake Prediction ◽  
Crustal Deformation ◽  
Large Earthquake ◽  
Viable Alternative ◽  
Earthquake Hazards ◽  
Seismic Shear ◽  
Stress Changes ◽  
Wave Splitting ◽  
Self Organised Criticality ◽  
Large Earthquakes

AbstractSelf-organised criticality of the crust appears to make deterministic earthquake prediction of time, place and magnitude of individual large earthquakes inherently impossible. This closes one line of approach to mitigating earthquake hazards. This paper suggests that a viable alternative to earthquake prediction is monitoring the build-up of stress before a large earthquake can occur. A new understanding of rock deformation allows stress changes to be monitored with seismic shear-wave splitting (seismic birefringence). With a suitable monitoring installation, this would allow the stochastic proximity of impending earthquakes to be recognised so that earthquakes could be forecast in the sense of recognising that crustal deformation was preparing for a large earthquake. Such stress-forecasting is not prediction, but, in many circumstances, a possible forecast crescendo of increasing urgency is exactly what is needed to best mitigate hazard to life and property.

Testing physics and statics based hybrid ETAS models

2021 ◽  
Author(s):  
Shubham Sharma ◽  
Shyam Nandan ◽  
Sebastian Hainzl
Keyword(s):  
Synthetic Data ◽  
Large Earthquake ◽  
Aftershock Sequence ◽  
Additional Stress ◽  
Etas Model ◽  
Epidemic Type Aftershock Sequence ◽  
Stress Changes ◽  
Alternative Approaches ◽  
Large Earthquakes ◽  
Model Approach

<p>Currently, the Epidemic Type Aftershock Sequence (ETAS) model is state-of-the-art for forecasting aftershocks. However, the under-performance of ETAS in forecasting the spatial distribution of aftershocks following a large earthquake make us adopt alternative approaches for the modelling of the spatial ETAS-kernel. Here we develop a hybrid physics and statics based forecasting model. The model uses stress changes, calculated from inverted slip models of large earthquakes, as the basis of the spatial kernel in the ETAS model in order to get more reliable estimates of spatiotemporal distribution of aftershocks. We evaluate six alternative approaches of stress-based ETAS-kernels and rank their performance against the base ETAS model. In all cases, an expectation maximization (EM) algorithm is used to estimate the ETAS parameters. The model approach has been tested on synthetic data to check if the known parameters can be inverted successfully. We apply the proposed method to forecast aftershocks of mainshocks available in SRCMOD database, which includes 192 mainshocks with magnitudes in the range between 4.1 and 9.2 occurred from 1906 to 2020. The probabilistic earthquake forecasts generated by the hybrid model have been tested using established CSEP test metrics and procedures. We show that the additional stress information, provided to estimate the spatial probability distribution, leads to more reliable spatiotemporal ETAS-forecasts of aftershocks as compared to the base ETAS model.</p>

scholarly journals Imaging ground surface deformations in post-disaster settings via small UAVs

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Richard L. Ybañez ◽  
Audrei Anne B. Ybañez ◽  
Alfredo Mahar Francisco A. Lagmay ◽  
Mario A. Aurelio
Keyword(s):  
Surface Deformation ◽  
Ground Surface ◽  
Point Clouds ◽  
Lateral Spreading ◽  
Fault Movement ◽  
Field Surveys ◽  
3D Point Clouds ◽  
Vertical Displacements ◽  
Resolution Imaging ◽  
Post Disaster

AbstractSmall unmanned aerial vehicles have been seeing increased deployment in field surveys in recent years. Their portability, maneuverability, and high-resolution imaging are useful in mapping surface features that satellite- and plane-mounted imaging systems could not access. In this study, we develop and apply a workplan for implementing UAV surveys in post-disaster settings to optimize the flights for the needs of the scientific team and first responders. Three disasters caused by geophysical hazards and their associated surface deformation impacts were studied implementing this workplan and was optimized based on the target features and environmental conditions. An earthquake that caused lateral spreading and damaged houses and roads near riverine areas were observed in drone images to have lengths of up to 40 m and vertical displacements of 60 cm. Drone surveys captured 2D aerial raster images and 3D point clouds leading to the preservation of these features in soft-sedimentary ground which were found to be tilled over after only 3 months. The point cloud provided a stored 3D environment where further analysis of the mechanisms leading to these fissures is possible. In another earthquake-devastated locale, areas hypothesized to contain the suspected source fault zone necessitated low-altitude UAV imaging below the treeline capturing Riedel shears with centimetric accuracy that supported the existence of extensional surface deformation due to fault movement. In the aftermath of a phreatomagmatic eruption and the formation of sub-metric fissures in nearby towns, high-altitude flights allowed for the identification of the location and dominant NE–SW trend of these fissures suggesting horst-and-graben structures. The workplan implemented and refined during these deployments will prove useful in surveying other post-disaster settings around the world, optimizing data collection while minimizing risk to the drone and the drone operators.

scholarly journals Stress relaxation arrested the mainshock rupture of the 2016 Central Tottori earthquake

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Yoshihisa Iio ◽  
Satoshi Matsumoto ◽  
Yusuke Yamashita ◽  
Shin’ichi Sakai ◽  
Kazuhide Tomisaka ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Focal Mechanism ◽  
Large Earthquake ◽  
Static Stress ◽  
Focal Mechanism Solutions ◽  
Large Earthquakes

AbstractAfter a large earthquake, many small earthquakes, called aftershocks, ensue. Additional large earthquakes typically do not occur, despite the fact that the large static stress near the edges of the fault is expected to trigger further large earthquakes at these locations. Here we analyse ~10,000 highly accurate focal mechanism solutions of aftershocks of the 2016 Mw 6.2 Central Tottori earthquake in Japan. We determine the location of the horizontal edges of the mainshock fault relative to the aftershock hypocentres, with an accuracy of approximately 200 m. We find that aftershocks rarely occur near the horizontal edges and extensions of the fault. We propose that the mainshock rupture was arrested within areas characterised by substantial stress relaxation prior to the main earthquake. This stress relaxation along fault edges could explain why mainshocks are rarely followed by further large earthquakes.

scholarly journals Structure-controlled asperities of the 1920 Haiyuan M8.5 and 1927 Gulang M8 earthquakes, NE Tibet, China, revealed by high-resolution seismic tomography

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Quan Sun ◽  
Shunping Pei ◽  
Zhongxiong Cui ◽  
Yongshun John Chen ◽  
Yanbing Liu ◽  
...  
Keyword(s):  
High Resolution ◽  
Seismic Tomography ◽  
High Velocity ◽  
Three Dimensional ◽  
Large Earthquake ◽  
Velocity Model ◽  
Tectonic Stress ◽  
Double Difference ◽  
Source Regions ◽  
Large Earthquakes

AbstractDetailed crustal structure of large earthquake source regions is of great significance for understanding the earthquake generation mechanism. Numerous large earthquakes have occurred in the NE Tibetan Plateau, including the 1920 Haiyuan M8.5 and 1927 Gulang M8 earthquakes. In this paper, we obtained a high-resolution three-dimensional crustal velocity model around the source regions of these two large earthquakes using an improved double-difference seismic tomography method. High-velocity anomalies encompassing the seismogenic faults are observed to extend to depths of 15 km, suggesting the asperity (high-velocity area) plays an important role in the preparation process of large earthquakes. Asperities are strong in mechanical strength and could accumulate tectonic stress more easily in long frictional locking periods, large earthquakes are therefore prone to generate in these areas. If the close relationship between the aperity and high-velocity bodies is valid for most of the large earthquakes, it can be used to predict potential large earthquakes and estimate the seismogenic capability of faults in light of structure studies.

3D Visual Technology of Geo-Deformation Disasters Induced by Mining Subsidence Based on ArcGIS Engine

2012 ◽  
Vol 500 ◽  
pp. 428-436 ◽  
Author(s):  
Ke Ming Yang ◽  
Jun Ting Ma ◽  
Bo Pang ◽  
Yi Bin Wang ◽  
Ran Wang ◽  
...  
Keyword(s):  
Coal Mining ◽  
Surface Deformation ◽  
Ground Deformation ◽  
Ground Surface ◽  
Horizontal Displacement ◽  
Mining Subsidence ◽  
Underground Coal Mining ◽  
Vertical Movements ◽  
Probability Integral Method ◽  
Arcgis Engine

Mining subsidence often produces significant horizontal and vertical movements at the ground surface, the surface deformation induced by underground coal mining can be predicted by probability integral method, and the surface geo-deformation disasters can be visualized based on GIS components. A three dimensional (3D) visualizing system of surface geo-deformation information is designed and developed with ArcGIS Engine and C# in the study. According to the surface deformation-predicted data induced by underground coal mining in Guobei Coalmine of Huaibei mine field, the extents and degrees of ground deformation disasters are visualized in 3D views for surface vertical subsidence, slope, curvature, horizontal displacement and horizontal strain based on the GIS-developed application platform.

scholarly journals Progressive Degradation of an Ice Rumple in the Thwaites Ice Shelf, Antarctica, as Observed from High-Resolution Digital Elevation Models

2018 ◽  
Vol 10 (8) ◽  
pp. 1236 ◽  
Author(s):  
Seung Hee Kim ◽  
Duk-jin Kim ◽  
Hyun-Cheol Kim
Keyword(s):  
High Resolution ◽  
Surface Deformation ◽  
Surface Expression ◽  
Deformation Model ◽  
Ice Shelf ◽  
Pressure Source ◽  
Viscoelastic Deformation ◽  
Shelf Stability ◽  
Transient Nature ◽  
Elevation Changes

Ice rumples are locally-grounded features of flowing ice shelves, elevated tens of meters above the surrounding surface. These features may significantly impact the dynamics of ice-shelf grounding lines, which are strongly related to shelf stability. In this study, we used TanDEM-X data to construct high-resolution DEMs of the Thwaites ice shelf in West Antarctica from 2011 to 2013. We also generated surface deformation maps which allowed us to detect and monitor the elevation changes of an ice rumple that appeared sometime between the observations of a grounding line of the Thwaites glacier using Double-Differential Interferometric SAR (DDInSAR) in 1996 and 2011. The observed degradation of the ice rumple during 2011–2013 may be related to a loss of contact with the underlying bathymetry caused by the thinning of the ice shelf. We subsequently used a viscoelastic deformation model with a finite spherical pressure source to reproduce the surface expression of the ice rumple. Global optimization allowed us to fit the model to the observed deformation map, producing reasonable estimates of the ice thickness at the center of the pressure source. Our conclusion is that combining the use of multiple high-resolution DEMs and the simple viscoelastic deformation model is feasible for observing and understanding the transient nature of small ice rumples, with implications for monitoring ice shelf stability.

scholarly journals Combined assimilation of streamflow and snow water equivalent for mid-term ensemble streamflow forecasts in snow-dominated regions

2016 ◽  
Author(s):  
Jean M. Bergeron ◽  
Mélanie Trudel ◽  
Robert Leconte
Keyword(s):  
Data Assimilation ◽  
State Vector ◽  
Snow Water Equivalent ◽  
Synthetic Data ◽  
Hydrologic Model ◽  
Open Loop ◽  
The State ◽  
Wide Range ◽  
Snow Water ◽  
The Impact

Abstract. The potential of data assimilation for hydrologic predictions has been demonstrated in many research studies. Watersheds over which multiple observation types are available can potentially further benefit from data assimilation by having multiple updated states from which hydrologic predictions can be generated. However, the magnitude and time span of the impact of the assimilation of an observation varies according not only to its type, but also to the variables included in the state vector. This study examines the impact of multivariate synthetic data assimilation using the Ensemble Kalman Filter (EnKF) into the spatially distributed hydrologic model CEQUEAU for the mountainous Nechako River located in British-Columbia, Canada. Synthetic data includes daily snow cover area (SCA), daily measurements of snow water equivalent (SWE) at three different locations and daily streamflow data at the watershed outlet. Results show a large variability of the continuous rank probability skill score over a wide range of prediction horizons (days to weeks) depending on the state vector configuration and the type of observations assimilated. Overall, the variables most closely linearly linked to the observations are the ones worth considering adding to the state vector. The performance of the assimilation of basin-wide SCA, which does not have a decent proxy among potential state variables, does not surpass the open loop for any of the simulated variables. However, the assimilation of streamflow offers major improvements steadily throughout the year, but mainly over the short-term (up to 5 days) forecast horizons, while the impact of the assimilation of SWE gains more importance during the snowmelt period over the mid-term (up to 50 days) forecast horizon compared with open loop. The combined assimilation of streamflow and SWE performs better than its individual counterparts, offering improvements over all forecast horizons considered and throughout the whole year, including the critical period of snowmelt. This highlights the potential benefit of using multivariate data assimilation for streamflow predictions in snow-dominated regions.

Sign in / Sign up

Export Citation Format

Share Document