Assessing the role of selected constraints in Bayesian dynamic source inversion: Application to the 2017 Mw 6.3 Lesvos earthquake

Summary A dynamic finite-fault source inversion for stress and frictional parameters of the Mw 6.3 2017 Lesvos earthquake is carried out. The mainshock occurred on June 12, offshore the southeastern coast of the Greek island of Lesvos in the north Aegean Sea. It caused 1 fatality, 15 injuries, and extensive damage to the southern part of the island. Dynamic rupture evolution is modeled on an elliptic patch, using the linear slip-weakening friction law. The inversion is posed as a Bayesian problem and the Parallel Tempering Markov Chain Monte Carlo algorithm is used to obtain posterior probability distributions by updating the prior distribution with progressively more constraints. To calculate the first posterior distribution, only the constraint that the model should expand beyond the nucleation patch is used. Then, we add the constraint that the model should reach a moment magnitude similar to that obtained from our centroid moment tensor inversion. For the final posterior distribution, 15 acceleration records from Greek and Turkish strong motion networks at near regional distances ($\approx 30 - 150$ km) in the frequency range of 0.05–0.15 Hz are used. The three posterior distributions are compared to understand how much each constraint contributes to resolving different quantities. The most probable values and uncertainties of individual parameters are also calculated, along with their mutual trade-offs. The features best determined by seismograms in the final posterior distribution include the position of the nucleation region, the mean direction of rupture (towards WNW), the mean rupture speed (with 68 per cent of the distribution lying between 1.4–2.6 km/s), radiated energy (12–65 TJ), radiation efficiency (0.09–0.38), and the mean stress drop (2.2–6.5 MPa).

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Comparison of local kinematic rupture joint inversion approaches for tsunami early warning: Examples of the 2017-2020 Mw > 6.3 East Aegean earthquakes

10.5194/egusphere-egu21-5221 ◽

2021 ◽

Author(s):

Malte Metz ◽

Marius Isken ◽

Rongjiang Wang ◽

Torsten Dahm ◽

Haluk Özener ◽

...

Keyword(s):

Early Warning ◽

Joint Inversion ◽

Moment Tensor ◽

Strong Motion ◽

Aegean Sea ◽

High Rate ◽

Source Inversion ◽

Dynamic Rupture ◽

Centroid Moment Tensor ◽

Tsunami Early Warning

The fast inversion of reliable centroid moment tensor and kinematic rupture parameters of earthquakes occurring near coastal margins is a key for the assessment of the tsunamigenic potential and early tsunami warning (TEW). In recent years, more and more multi-channel seismic and geodetic online station networks have been built-up to improve the TEW, for instance the GNSS and strong motion networks in Italy, Greece, and Turkey, additionally to the broadband seismological monitoring. Inclusion of such data for the fast kinematic source inversion can improve the resolution and robustness of its&#8217; solutions. However, methods have to be further developed and tested to fully exploit the potential of such rich joint dataset.In this frame, we compare and test two in-house developed, kinematic / dynamic rupture inversion methods which are based on completely different approaches. The IDS (Iterative Deconvolution and Stacking, Zhang et al., 2014) combines an iterative seismic network inversion with back projection techniques to retrieve subfault source time functions. The pseudo dynamic rupture model (Dahm et al., in review) links the rupture front propagation estimate based on the Eikonal equation with the dislocation derived from a boundary element method to model dislocation snapshots. We used the latter in both a fast rupture estimate and a fully probabilistic source inversion.We use some Mw > 6.3 earthquakes that occurred in the coastal range of the Aegean Sea as an example for comparison: the Mw 6.3 Lesbos earthquake (12 June 2017), the Mw 6.6 Bodrum earthquake (20 July 2017), and the recent Mw 7.0 earthquake which occurred at Samos on 30 October 2020. The latter earthquake and the resulting tsunami caused fatalities and severe damage at the shorelines of Samos and around the city of Izmir, Turkey. The fast estimates are based on only little data and/or prior information obtained from the regional seismicity catalogue and available active fault information. The large number of seismic (broadband, strong motion) and geodetic (high-rate GNSS) stations in local and regional distance from the earthquake with good azimuthal coverage jointly inverted with InSAR data allows for robust inversion results. These, and other solutions, are used as a reference for the comparison of our fast source estimates. Preliminary results of the slip distribution and the source time function are in good agreement with modelling results from other authors.We present our insights into the kinematics of the chosen earthquakes investigated by means of joint inversions. Finally, the accuracy of our first fast source estimates, which could be of potential use in tsunami early warning, will be discussed.

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A user-friendly probabilistic earthquake source inversion framework for joint inversion of seismic, geodetic, and gravitational signals - The Grond toolkit

10.5194/egusphere-egu2020-18973 ◽

2020 ◽

Author(s):

Sebastian Heimann ◽

Marius Isken ◽

Daniela Kühn ◽

Hannes Vasyura-Bathke ◽

Henriette Sudhaus ◽

...

Keyword(s):

Open Source ◽

Joint Inversion ◽

Moment Tensor ◽

Source Parameters ◽

Seismic Source ◽

Magma Ascent ◽

Caldera Collapse ◽

Waveform Data ◽

Trade Offs ◽

Finite Fault

Seismic source and moment tensor waveform inversion is often ill-posed or non-unique if station coverage is poor or signals are weak. Three key ingredients can help in these situations: (1) probabilistic inference and global search of the full model space, (2) joint optimisation with datasets yielding complementary information, and (3) robust source parameterisation or additional source constraints. These demands lead to vast technical challenges, on the performance of forward modelling, on the optimisation algorithms, as well as on visualisation, optimisation configuration, and management of the datasets. Implementing a high amount of automation is inevitable.To tackle all these challenges, we are developing a sophisticated new seismic source optimisation framework, Grond. With its innovative Bayesian bootstrap optimiser, it is able to efficiently explore large model spaces, the trade-offs and the uncertainties of source parameters. The program is highly flexible with respect to the adaption to specific source problems, the design of objective functions, and the diversity of empirical datasets.It uses an integrated, robust waveform data processing, and allows for interactive visual inspection of many aspects of the optimisation problem, including visualisation of the result uncertainties. Grond has been applied to CMT moment tensor and finite-fault optimisations at all scales, to nuclear explosions, to a meteorite atmospheric explosion, and to volcano-tectonic processes during caldera collapse and magma ascent. Hundreds of seismic events can be handled in parallel given a single optimisation setup.Grond can be used to optimise simultaneously seismic waveforms, amplitude spectra, waveform features, phase picks, static displacements from InSAR and GNSS, and gravitational signals.Grond is developed as an open-source package and community effort. It builds on and integrates with other established open-source packages, like Kite (for InSAR) and Pyrocko (for seismology).

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The Mw 7.6 Dusky Sound earthquake of 2009

Bulletin of the New Zealand Society for Earthquake Engineering ◽

10.5459/bnzsee.43.1.24-40 ◽

2010 ◽

Vol 43 (1) ◽

pp. 24-40 ◽

Cited By ~ 13

Author(s):

Bill Fry ◽

Stephen Bannister ◽

John Beavan ◽

Lara Bland ◽

Brendon Bradley ◽

...

Keyword(s):

Moment Tensor ◽

Seismic Energy ◽

Rupture Directivity ◽

Centroid Moment Tensor ◽

M Wave ◽

Radiated Seismic Energy ◽

Australian Plate ◽

Finite Fault ◽

Minimal Damage ◽

Sparse Population

The Mw 7.6 Dusky Sound earthquake of July 15th, 2009, was the largest magnitude earthquake in New Zealand since the devastating 1931 Hawke’s Bay event (Ms 7.8). The earthquake was sufficiently large to generate at least a 2.3 m wave at Passage Point. Despite its large magnitude, this event resulted in relatively minimal damage when compared to worldwide events of a similar size. This can be explained as a fortunate combination of the sparse population of the area and the specific physical characteristics of the earthquake. Centroid Moment Tensor (CMT) solutions define the rupture surface as a low-angle plane and finite fault inversions confirm the slip occurred on the interface between the eastward-subducting Australian plate and overriding Pacific plate, initiating at about 30 km depth and rupturing upward and southwestward to about 15 km depth. The oceanward rupture directivity likely contributed to the lower intensity of measured ground motion than might be expected for such a large, shallow event. The amount of radiated seismic energy from the earthquake was relatively small, and far fewer landslides were triggered from this event than from the 2003 Mw 7.2 Fiordland event.

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3-D joint geodetic and strong-motion finite fault inversion of the 2008 May 12, Wenchuan, China Earthquake

Geophysical Journal International ◽

10.1093/gji/ggaa239 ◽

2020 ◽

Vol 222 (2) ◽

pp. 1390-1404

Author(s):

Leonardo Ramirez-Guzman ◽

Stephen Hartzell

Keyword(s):

Time Window ◽

Joint Inversion ◽

Strong Motion ◽

Multiple Time ◽

Source Inversion ◽

Geodetic Inversion ◽

Finite Fault Inversion ◽

Finite Fault ◽

China Earthquake ◽

The Moment

SUMMARY We present a source inversion of the 2008 Wenchuan, China earthquake, using strong-motion waveforms and geodetic offsets together with 3-D synthetic ground motions. We applied the linear multiple time window technique considering geodetic and dynamic Green's functions computed with the finite-element method and the reciprocity and Strain Green's Tensor formalism. All ground motion estimates, valid up to 1 Hz, accounted for 3-D effects, including the topography and the geometry of the Beichuan and Pengguan faults. Our joint inversion has a higher moment (M0) than a purely geodetic inversion and the slip distribution presents differences when compared to 1-D model source inversions. The moment is estimated to be M0 = 1.2 × 1021 N·m, slightly larger than other works. Our results show that considering a complex 3-D structure reduces the size of large areas of 10 m slip or greater by distributing it in wider zones, with reduced slips, in the central portion of the Beichuan and the Pengguan faults. Finally, we compare our source with a relocated aftershock catalogue and conclude that the 4–5 m slip contours approximately bound the absence or presence of aftershocks.

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Rupture process of the 7 May 2020 Mw 5.0 Tehran earthquake and its relation with the Damavand stratovolcano, and Mosha Fault

10.5194/egusphere-egu21-1759 ◽

2021 ◽

Author(s):

Pınar Büyükakpınar ◽

Mohammadreza Jamalreyhani ◽

Mehdi Rezapour ◽

Stefanie Donner ◽

Nima Nooshiri ◽

...

Keyword(s):

Moment Tensor ◽

Source Parameters ◽

Active Faults ◽

Strong Motion ◽

Fault Model ◽

Focal Mechanism Solution ◽

Strong Motion Records ◽

Finite Fault ◽

Finite Fault Model ◽

Mosha Fault

In May 2020 an earthquake with Mw 5.0 struck at ~40 km east of Tehran metropolis and ~15 km south of the Damavand stratovolcano. It was responsible for 2 casualties and 23 injured. The mainshock was preceded by a foreshock with Ml 2.9 and followed by a significant aftershock sequence, including ten events with Ml 3+. The occurrence of this event raised the question of its relation with volcanic activities and/or concern about the occurrence of larger future earthquakes in the capital of Iran. Tehran megacity is surrounded by several inner-city and adjacent active faults that correspond to high-risk seismic sources in the area. The Mosha fault with ~150 km long is one of the major active faults in central Alborz and east of Tehran. It has hosted several historical earthquakes (i.e. 1665 Mw 6.5 and 1830 Mw 7.1 earthquakes) in the vicinity of the 2020 Mw 5.0 Tehran earthquake&#8217;s hypocenter. In this study, we evaluate the seismic sequence of the Tehran earthquake and obtain the full moment tensor inversion of this event and its larger aftershocks, which is a key tool to discriminate between tectonic and volcanic earthquakes. Furthermore, we obtain a robust characterization of the finite fault model of this event applying probabilistic earthquake source inversion framework using near-field strong-motion records and broadband seismograms, with an estimation of the uncertainties of source parameters. Due to the relatively weak magnitude and deeper centroid depth (~12 km), no static surface displacement was observed in the coseismic interferograms, and modeling performed by seismic records. Focal mechanism solution from waveform inversion, with a significant double-couple component, is compatible with the orientation of the sinistral north-dipping Mosha fault at the centroid location. The finite fault model suggests that the mainshock rupture propagated towards the northwest. This directivity enhanced the peak acceleration in the direction of rupture propagation, observed in strong-motion records. The 2020 moderate magnitude earthquake with 2 casualties, highlights the necessity of high-resolution seismic monitoring in the capital of Iran, which is exposed to a risk of destructive earthquakes with more than 10 million population. Our results are important for the hazard and risk assessment, and the forthcoming earthquake early warning system development in Tehran metropolis.

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Dynamic source inversion of the 2014 Mw6 South Napa, California, earthquake

10.5194/egusphere-egu2020-18422 ◽

2020 ◽

Author(s):

Jan Premus ◽

Frantisek Gallovic

Keyword(s):

Monte Carlo ◽

Strong Motion ◽

Inversion Method ◽

Source Inversion ◽

Dynamic Rupture ◽

Dynamic Simulations ◽

Simulation Code ◽

Strong Motion Data ◽

Motion Data ◽

Dynamic Source

Dynamic rupture modeling coupled with strong motion data fitting (dynamic source inversion) offers an insight into the rupture physics, constraining and enriching information gained from standard kinematic slip inversions. We utilize the Bayesian Monte Carlo dynamic source inversion method introduced recently by Gallovi&#269; et al. (2019), which, in addition to finding a best-fitting model, allows assessing uncertainties of the inferred parameters by sampling the posterior probability density function. The Monte Carlo approach requires running a large number (millions) of dynamic simulations due to the nonlinearity of the inverse problem. It is achieved by using GPU accelerated dynamic rupture simulation code FD3D_TSN (Premus et al., submitted) as a forward solver. We apply the inversion to the 2014 Mw6 South Napa, California, earthquake, employing strong motion data (up to 0.5 Hz) from the 10 closest stations. As an output, we obtain samples of the spatial distributions of dynamic parameters (prestress and parameters of the slip-weakening friction law). Regarding the rupture geometry, we consider two, presently ambiguous, fault planes (Pollitz et al., 2019), showing considerable differences in fitting seismograms in very close vicinity of the fault. We investigate properties of the rupture, especially in the region close to the free surface, and the viability of the model samples to explain the observed data in a broader frequency range (up to 5Hz).

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A Teleseismic Study of the 2002 Denali Fault, Alaska, Earthquake and Implications for Rapid Strong-Motion Estimation

Earthquake Spectra ◽

10.1193/1.1778388 ◽

2004 ◽

Vol 20 (3) ◽

pp. 617-637 ◽

Cited By ~ 17

Author(s):

Chen Ji ◽

Don V. Helmberger ◽

David J. Wald

Keyword(s):

Moment Tensor ◽

Strong Motion ◽

P Wave ◽

Phase Iii ◽

Peak Ground Velocity ◽

Centroid Moment Tensor ◽

Waveform Data ◽

Arrival Times ◽

Denali Fault ◽

Alaska Earthquake

Slip histories for the 2002 M7.9 Denali fault, Alaska, earthquake are derived rapidly from global teleseismic waveform data. In phases, three models improve matching waveform data and recovery of rupture details. In the first model (Phase I), analogous to an automated solution, a simple fault plane is fixed based on the preliminary Harvard Centroid Moment Tensor mechanism and the epicenter provided by the Preliminary Determination of Epicenters. This model is then updated (Phase II) by implementing a more realistic fault geometry inferred from Digital Elevation Model topography and further (Phase III) by using the calibrated P-wave and SH-wave arrival times derived from modeling of the nearby 2002 M6.7 Nenana Mountain earthquake. These models are used to predict the peak ground velocity and the shaking intensity field in the fault vicinity. The procedure to estimate local strong motion could be automated and used for global real-time earthquake shaking and damage assessment.

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Rupture parameters of dynamic source models compatible with NGA-West2 GMPEs

10.5194/egusphere-egu2020-16610 ◽

2020 ◽

Author(s):

Frantisek Gallovic ◽

Lubica Valentova

Keyword(s):

Ground Motions ◽

Source Parameters ◽

Strong Motion ◽

Seismic Hazard Assessment ◽

Response Spectra ◽

Maximum Magnitude ◽

Source Inversion ◽

Dynamic Rupture ◽

Heterogeneous Distribution ◽

Dynamic Source

Dynamic source inversions of individual earthquakes provide constraints on stress and frictional parameters, which are inherent to the studied event. However, general characteristics of both kinematic and dynamic rupture parameters are not well known, especially in terms of their variability. Here we constrain them by creating and analyzing a synthetic event database of dynamic rupture models that generate waveforms compatible with strong ground motions in a statistical sense.We employ a framework that is similar to the Bayesian dynamic source inversion by Gallovi&#269; et al. (2019). Instead of waveforms of a single event, the data are represented by Ground Motion Prediction Equations (GMPEs), namely NGA-West2&#160; (Boore et al., 2014). The Markov chain Monte Carlo technique produces samples of the dynamic source parameters with heterogeneous distribution on a fault. For all simulations, we assume a vertical 36x20km strike-slip fault, which limits our maximum magnitude to Mw<7. For dynamic rupture calculations, we employ upgraded finite-difference code FD3D_TSN (Premus et al., 2020) with linear slip-weakening friction law. Seismograms are calculated on a regular grid of phantom stations assuming a 1D velocity model using precalculated full wavefield Green's functions. The procedure results in a database with those dynamic rupture models that generate ground motions compatible with the GMPEs (acceleration response spectra in period band 0.5-5s) in terms of both median and variability.The events exhibit various magnitudes and degrees of complexity (e.g. one or more asperities). We inspect seismologically determinable parameters, such as duration, moment rate spectrum, stress drop, size of the ruptured area, and energy budget, including their variabilities.&#160; Comparison with empirically derived values and scaling relations suggests that the events are compatible with real earthquakes (Brune, 1970, Kanamori and Brodsky, 2004). Moreover, we investigate the stress and frictional parameters in terms of their scaling, power spectral densities, and possible correlations. The inferred statistical properties of the dynamic source parameters can be used for physics-based strong-motion modeling in seismic hazard assessment.

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A Testable Worldwide Earthquake Faulting Mechanism Model

Seismological Research Letters ◽

10.1785/0220200445 ◽

2021 ◽

Author(s):

Matteo Taroni ◽

Jacopo Selva

Keyword(s):

Simple Model ◽

Moment Tensor ◽

A Priori ◽

Testing Procedure ◽

Global Scale ◽

Focal Mechanisms ◽

Source Inversion ◽

Source Characterization ◽

Centroid Moment Tensor ◽

Mechanism Model

Abstract In this article, we present a simple model to forecast global focal mechanisms. This model is based on a simple discrete counting distribution of the global centroid moment tensor catalog, and it also includes, using a Bayesian scheme, the a priori information from the Anderson theory of faulting. Our model is tested in hindcasting mode against independent data of global large earthquakes with Ms≥7. We obtained statistically significant good agreement between model and data using consistency test, demonstrating that this simple model can satisfactorily forecast focal mechanisms at the global scale. The defined testing procedure can be used to test the model in prospective mode against future events. These forecasts may inform short- to long-term hazard quantifications that require a finite source characterization, as well as real-time source inversion algorithms.

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Complex rupture dynamics of the 2020 Mw 6.8 Elazığ (Sivrice) earthquake, Turkey

10.5194/egusphere-egu21-14875 ◽

2021 ◽

Author(s):

František Gallovič ◽

Jiří Zahradník ◽

Vladimír Plicka ◽

Efthimios Sokos ◽

Christos Evangelidis ◽

...

Keyword(s):

Strong Motion ◽

Early Warning Systems ◽

Aftershock Sequence ◽

P Wave ◽

Multiple Point ◽

Rupture Propagation ◽

Source Inversion ◽

Frequency Range ◽

Dynamic Rupture ◽

Seismic Engineering

The 2020 Mw 6.8 Elaz&#305;&#287; (Sivrice) earthquake occurred on the P&#252;t&#252;rge segment of the East Anatolian Fault zone. This strike-slip segment is situated between strong earthquakes that happened 100&#8211;150 years ago, and, since that time, the segment remained with eight Mw5-6 events, but with no Mw 6+. We relocate the mainshock and aftershock sequence and infer basic characteristics of the event using the ISOLA multiple point source approach and backpropagation of S-waveforms from local strong-motion recordings. Together with clear secondary P wave onsets identified in the recordings, the results suggest complex rupture propagation with reversal of the rupture propagation. We apply a recently developed Bayesian dynamic source inversion with slip-weakening friction and spatially inhomogeneous stress and friction parameters to gain better insight into the rupture process. Using high-quality near field recordings in the low-frequency range (<0.3Hz), we obtain a complex dynamic rupture model explaining the weak rupture initiation followed by a cascade of at least three rupture episodes, including the rupture reversal. The dynamic model explains significant features of the recordings even in a broader frequency range interesting for seismic engineering applications (<2.5Hz), e.g., a directivity pulse associated with rupturing the event&#8217;s strongest asperity with 4 m of slip and local stress drop of 40 MPa. We show that by reducing the initial stress in the top 10 km by 10%, the rupture fails to develop into the larger event, finishing as an Mw 5.8 earthquake. Considering the latter experiment corresponds to an earlier state of the fault in the seismic cycle, we hypothesize that the interseismic M5+ events on the P&#252;t&#252;rge segment were undeveloped rudiments of potentially large events. Thus, the fault seems to have been ready for the Mw6.8 earthquake only by the time of the earthquake occurrence in 2020. This suggests that at the time of the Elaz&#305;&#287; earthquake initiation, the final Mw6.8 magnitude was not determined, making it a treacherous case for early warning systems.

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