A Testable Worldwide Earthquake Faulting Mechanism Model

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.

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

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

<p>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’ solutions. However, methods have to be further developed and tested to fully exploit the potential of such rich joint dataset.</p><p>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.</p><p>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.<br>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.<br>Preliminary results of the slip distribution and the source time function are in good agreement with modelling results from other authors.</p><p>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.</p>

Bayesian multiple rupture plane inversion to assess rupture complexity: application to the 2018 Mw 7.9 Alaska earthquake

2021 ◽  
Author(s):  
Angela Carrillo Ponce ◽  
Torsten Dahm ◽  
Simone Cesca ◽  
Frederik Tilmann ◽  
Andrey Babeyko ◽  
...  
Keyword(s):  
Moment Tensor ◽  
Real Data ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Strike Slip Fault ◽  
Body Waves ◽  
Source Inversion ◽  
Lateral Strike Slip ◽  
Double Couple ◽  
Alaska Earthquake

<p>When the earthquake rupture is complex and ruptures of multiple fault segments contribute to the total energy release, the produced wavefield is the superposition of individual signals produced by single subevents. Resolving source complexity for large, shallow earthquakes can be used to improve ground shaking and surface slip estimations, and thus tsunami models. The 2018 Mw 7.9 Alaska earthquake showed such complexity: according to previous studies, the rupture initiated as a right-lateral strike-slip fault on a N-S oriented fault plane, but then jumped onto a left-lateral strike-slip fault oriented westward. Rupture complexity and presence of multiple subevents may characterize a number of other earthquakes. However, even when individual subevents are spatially and/or temporally separated, it is very difficult to identify them from far field recordings. In order to model complex earthquakes we have implemented a multiple double couple inversion scheme within Grond, a tool devoted to the robust characterization of earthquake source parameters included in the Pyrocko software. Given the large magnitude of the target earthquake, we perform our source inversions using broadband body waves data (P and S phases) at teleseismic distances. Our approach starts with a standard moment tensor inversion, which allows to get more insights about the centroid location and overall moment release. These values can then be used to constrain the double source inversion. We discuss the performance of the inversion for the Alaska earthquake, using synthetic and real data. First, we generated realistic synthetic waveforms for a two-subevents source, assuming double couple sources with the strike-slip mechanisms proposed for the Alaska earthquake. We model the synthetic dataset both using a moment tensor and a double double couple source, and demonstrate the stability of the double double couple inversion, which is able to reconstruct the two focal mechanisms, the moment ratio and the relative centroid locations of the two subevents. Synthetic tests show that the inversion accuracy can be in some cases reduced, in presence of noisy data and when the interevent time between subevents is short. A larger noise addition affects the retrieval of the focal mechanism orientations only in some cases, but in general all the parameters were well retrieved. Then, we test our tool using real data for the earthquake. The single source inversion shows that the centroid is shifted 27 s in time and 40 km towards NE with respect to the original assumed location retrieved from the gCMT catalogue. The following double double couple source inversion resolves two subevents with right-lateral and left-lateral strike-slip focal mechanisms and Mw 7.6 and 7.8 respectively. The subevent centroids are separated by less than 40 km in space and less than 20 s in time.</p>

scholarly journals The Reliance of the Earthquake B-Value on Depth and Focal Mechanism

2021 ◽  
Vol 54 (1D) ◽  
pp. 1-10
Author(s):  
Emad Al-Heety
Keyword(s):  
Moment Tensor ◽  
Focal Depth ◽  
Seismic Hazard Assessment ◽  
B Value ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Likelihood Method ◽  
Centroid Moment Tensor ◽  
B Values ◽  
Completeness Magnitude

The earthquake size distribution (b-value) is a significant factor to recognize the seismic activity, seismotectonic, and seismic hazard assessment. In the current work, the connection of the b-constant value with the focal depth and mechanism was studied. The effect of the study scale (global, regional and local) on the dependence of b-value on the focal mechanisms was investigated. The database is quoted from the Global Centroid Moment Tensor catalog. The selected earthquakes are the shallow normal, reverse and strike-slip events. The completeness magnitude (Mc) is 5.3. The maximum likelihood method is utilized to compute the b-value. The obtained results show that the b-value is decreasing with depth to range 10-20 km, then increases to the depth of 40km. The turning point of b-value (increasing of b-value) locates at the depth of the transition brittle-ductile zone. Globally and regionally, low, moderate, and high b-values are associated with reverse, strike-slip, and normal focal mechanisms, respectively, while locally, the relation between b-values and focal mechanisms shows different association trends, such as low, moderate, and high b-values are associated with normal, strike-slip, and reverse focal mechanisms and so on.

scholarly journals Earthquake source characterization by machine learning algorithms applied to acoustic signals

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bernabe Gomez ◽  
Usama Kadri
Keyword(s):  
Machine Learning ◽  
Information Dissemination ◽  
Effective Properties ◽  
Statistical Significance ◽  
Moment Tensor ◽  
Learning Algorithms ◽  
Machine Learning Algorithms ◽  
Acoustic Properties ◽  
Source Characterization ◽  
Centroid Moment Tensor

AbstractUnderwater seismic events generate acoustic radiation (such as acoustic-gravity waves), that carries information about the source and can travel long distances before dissipating. Effective early warning, emergency response, and information dissemination for earthquakes and tsunamis require a rapid characterisation of the fault properties: geometry and dynamics. In this work, we analysed hydrophone recordings of 201 earthquakes, located in the Pacific and the Indian Ocean, by employing acoustic signal processing and classification methods. The analysis allows identifying the type of earthquake (i.e. slip type, magnitude) and provides near real-time estimation of the effective properties of the fault dynamics and geometry. The results were compared against values reported by the Harvard Global Centroid Moment Tensor catalog (gCMT), revealing statistical significance between the extracted acoustic properties used to feed machine learning algorithms and the predicted slip and magnitude values.

Regional Moment Tensor Analysis in the Philippines: CMT Solutions in 2012–2013

2015 ◽  
Vol 10 (1) ◽  
pp. 18-24 ◽  
Author(s):  
Jun D. Bonita ◽  
◽  
Hiroyuki Kumagai ◽  
Masaru Nakano ◽  
◽  
...  
Keyword(s):  
Moment Tensor ◽  
The Philippines ◽  
Focal Mechanisms ◽  
Source Analysis ◽  
Centroid Moment Tensor ◽  
Large Size ◽  
Moment Tensor Analysis ◽  
Analysis System ◽  
Swift System ◽  
Seismographic Network

Recently, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) has upgraded its seismic network, equipping it with accelerometers and broadband seismometers for intensity and focal mechanism determinations. As part of this upgrade, PHIVOLCS adapted the use of a source analysis system called SWIFT to determine the centroid moment tensor (SWIFT CMT). SWIFT CMT solutions were estimated for medium to large size earthquakes (4.1 ≤Mw≤ 7.6) in the Philippines for the period of January 2012 to November 2013 and were statistically evaluated with respect to the CMT solutions of the Global Centroid Moment Tensor (GCMT) Project. The seismic moments, moment magnitudes, centroid locations, depths and focal mechanisms of most of the SWIFT CMT solutions are found to be consistent to those of the GCMT solutions for earthquakes withMw≥ 4.6. The SWIFT system with the new broadband seismographic network provides more CMT solutions for moderate size earthquakes (Mw≥ 4.1) than GCMT. SWIFT proves to be useful in the development of the Philippines CMT catalogue that will lead to a better understanding of seismotectonics in the Philippines.

scholarly journals Focal Mechanisms of Mw 6.3 Aftershocks from Waveform Inversions, Phayao Fault Zone, Northern Thailand

2017 ◽  
Vol 2017 ◽  
pp. 1-7 ◽  
Author(s):  
Kasemsak Saetang
Keyword(s):  
Fault Zone ◽  
Moment Tensor ◽  
Waveform Inversion ◽  
Focal Mechanisms ◽  
Frequency Noise ◽  
Source Inversion ◽  
Fault Plane Solutions ◽  
Northern Thailand ◽  
Moment Tensors ◽  
Grid Search Method

The focal mechanisms of Mw 6.3 aftershocks, Chiang Rai Province, Northern Thailand, were determined by using a multistation waveform inversion. Three aftershocks were selected and their waveforms were inverted for moment tensor calculation. Waveform inversions were derived from three broadband stations with three components and epicentral distances less than 250 km after all seismic stations were considered. The deviatoric moment tensor inversion was used for focal mechanism calculations. Band-pass filtering in the range of 0.03–0.15 Hz was selected for reducing low- and high-frequency noise. Source positions were created by using a single-source inversion and a grid-search method computed to optimize the waveform match. The results showed stable moment tensors and fault geometries with the southwest azimuth in the northern part of the Payao Fault Zone (PFZ) with depths shallower than 10 km. Left-lateral strike-slip with a reverse component was detected. The tectonics of the PFZ is constrained by fault-plane solutions of earthquakes. WSW directional strikes are observed in the northern part of the PFZ.

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

2021 ◽  
Author(s):  
Filip Kostka ◽  
Jiří Zahradník ◽  
Efthimios Sokos ◽  
František Gallovič
Keyword(s):  
Posterior Distribution ◽  
Moment Tensor ◽  
Strong Motion ◽  
Monte Carlo Algorithm ◽  
Source Inversion ◽  
Dynamic Rupture ◽  
Centroid Moment Tensor ◽  
Trade Offs ◽  
Finite Fault ◽  
The Mean

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).

scholarly journals Fully probabilistic seismic source inversion – Part 1: Efficient parameterisation

2013 ◽  
Vol 5 (2) ◽  
pp. 1125-1162 ◽  
Author(s):  
S. C. Stähler ◽  
K. Sigloch
Keyword(s):  
Moment Tensor ◽  
Source Parameters ◽  
Practical Importance ◽  
Principal Component ◽  
Seismic Source ◽  
Empirical Orthogonal Functions ◽  
Time Function ◽  
Source Inversion ◽  
Source Time Function ◽  
Earthquake Parameters

Abstract. Seismic source inversion is a non-linear problem in seismology where not just the earthquake parameters themselves, but also estimates of their uncertainties are of great practical importance. Probabilistic source inversion (Bayesian inference) is very adapted to this challenge, provided that the parameter space can be chosen small enough to make Bayesian sampling computationally feasible. We propose a framework for PRobabilistic Inference of Source Mechanisms (PRISM) that parameterises and samples earthquake depth, moment tensor, and source time function efficiently by using information from previous non-Bayesian inversions. The source time function is expressed as a weighted sum of a small number of empirical orthogonal functions, which were derived from a catalogue of >1000 STFs by a principal component analysis. We use a likelihood model based on the cross-correlation misfit between observed and predicted waveforms. The resulting ensemble of solutions provides full uncertainty and covariance information for the source parameters, and permits to propagate these source uncertainties into travel time estimates used for seismic tomography. The computational effort is such that routine, global estimation of earthquake mechanisms and source time functions from teleseismic broadband waveforms is feasible.

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