gWFM: A Global Catalog of Moderate-Magnitude Earthquakes Studied Using Teleseismic Body Waves

2020 ◽  
Vol 92 (1) ◽  
pp. 212-226
Author(s):  
Sam Wimpenny ◽  
C. Scott Watson
Keyword(s):  
Moment Tensor ◽  
Source Parameters ◽  
Body Waves ◽  
Earthquake Catalog ◽  
Centroid Moment Tensor ◽  
Waveform Modeling ◽  
Crustal Earthquakes ◽  
Earthquake Source Parameters ◽  
Double Couple ◽  
Moderate Magnitude

Abstract We present a compilation of 2131 high-fidelity mechanisms and centroid depths of moderate-magnitude earthquakes derived using synthetic body-waveform modeling (the Global Waveform-Modelled Earthquake Catalog v1.0—gWFM), which can be visualized and downloaded online (see Data and Resources). In this article, we describe the methods used to construct the gWFM and present a comparison between the earthquake depths and focal mechanisms in the gWFM with those derived by the International Seismological Centre, Global Centroid Moment Tensor (Global CMT) project, and the U.S. Geological Survey (USGS) W-phase, as well as 60 events studied using geodesy. We find that 20%–30% of the earthquakes in routine global catalogs have depths that differ by more than 10 km from those in the gWFM. Shallow-crustal earthquakes of Mw 5–6 are typically the worst located in depth by routine catalogs. Over 90% of the earthquakes in the gWFM are within ±15° in strike, ±5° in dip, and ±15° in rake of the Global CMT and USGS W-phase best double-couple moment tensor solutions. However, the mechanisms of shallow Mw 5–6 earthquakes in the routine catalogs can be inaccurate, due to the well-known insensitivity of long-period surface waves to the vertical dip-slip components of the moment tensor. The gWFM is an archive of well-constrained earthquake source parameters, though it will continue to update as new earthquake mechanisms and depths are published, thereby remaining an up-to-date research tool.

The Meckering earthquake of 14 October 1968: A possible downward propagating rupture

1987 ◽  
Vol 77 (5) ◽  
pp. 1558-1578
Author(s):  
Kristín S. Vogfjörd ◽  
Charles A. Langston
Keyword(s):  
Moment Tensor ◽  
Source Parameters ◽  
Time History ◽  
Vertical Displacement ◽  
Body Waves ◽  
Finite Fault ◽  
Short Period ◽  
Double Couple ◽  
The Moment ◽  
Fault Length

Abstract Average source parameters of the 1968 Meckering, Australia earthquake are obtained by the inversion of body waves. The objectives of the inversion are the elements of the moment tensor and the source-time history. An optimum source depth of 3 km is determined, but because of source complexity the point source assumption fails and the moment tensor obtained at that depth has a large nondouble-couple term, compensated linear vector dipole = 34 per cent. The source parameters of the major double-couple are: strike = 341°; dip = 37°; rake = 61°; and seismic moment = 8.2 ×1025 dyne-cm. The source-time function is of approximately 4 sec duration, with a long rise time and a sharp fall-off. The fault length is constrained on the surface by the observed surface break, and results from vertical displacement modeling suggest a width of approximately 10 km in the middle, assuming a dip of 37°. That restricts the entire faulted area to lie above 6 km depth. Two finite fault models for the earthquake are presented, with rupture initiating at a point (1) near the top of the fault and (2) at the bottom of the fault. Both models produce similar long-period synthetics, but based on the short-period waveforms, model 1 is favored. It is argued that such a rupture process is the most reasonable in this cold shield region.

scholarly journals Teleseismic body wave inversion

2018 ◽  
Vol 40 (3) ◽  
pp. 1177
Author(s):  
A. Moshou ◽  
P. Papadimitriou ◽  
K. Makropoulos
Keyword(s):  
Body Wave ◽  
Moment Tensor ◽  
Source Parameters ◽  
Singular Value Decomposition Method ◽  
Wave Inversion ◽  
Generalized Inversion ◽  
Earthquake Source Parameters ◽  
Generalized Inversion Technique ◽  
Double Couple ◽  
Value Decomposition

Body wave inversion methodology is developed to determine the earthquake source parameters in teleseismic distances. The generalized inversion technique, based on the singular value decomposition method, is applied to determine the deviatone moment tensor which is decomposed in two parts. The first one is related to the pure Double Couple (DC) and the second one to the compensated linear vector dipoles (CLVD). The best solution of the overdetermined problem is obtained by minimizing the misfit between observed and synthetic seismograms. The proposed methodology is applied for the four strongest earthquakes that occurred recently in Greece (2001-2006)

scholarly journals Source parameters estimation of the 1980 Bajhang Earthquake, far western Nepal

1997 ◽  
Vol 15 ◽  
Author(s):  
K. N. Khanal
Keyword(s):  
Source Parameters ◽  
Parameters Estimation ◽  
Depth Of Focus ◽  
Source Time Function ◽  
Waveform Modeling ◽  
Motion Data ◽  
Earthquake Source Parameters ◽  
First Motion ◽  
The Himalaya ◽  
Moderate Magnitude

The Bajhang earthquake of 1980 is one of the moderate magnitude earthquakes in the Himalaya that has been investigated by many researchers. The methods used by them for determining source parameters vary from the use of the first motion data to the waveform modeling. The ambiguity in focal mechanisms determined by different processes has been resolved by comparing the synthetic seismograms generated using wavenumber integration technique with those observed at the Global Digital Seismograph Networks (GDSN).The earthquake source parameters determined are found to be as follows: Dip=26°, Strike=290°, Rake=90°, Depth of focus=20±5 km and source time function=7 (2, 3, 2) seconds.

Strain to Ground Motion Conversion of DAS Data for Earthquake Magnitude and Stress Drop Determination

2021 ◽  
Author(s):  
Itzhak Lior ◽  
Anthony Sladen ◽  
Diego Mercerat ◽  
Jean-Paul Ampuero ◽  
Diane Rivet ◽  
...  
Keyword(s):  
Early Warning ◽  
Stress Drop ◽  
Source Parameters ◽  
Simulated Data ◽  
Earthquake Early Warning ◽  
Body Waves ◽  
Ocean Bottom ◽  
Correlated Noise ◽  
S Wave ◽  
Earthquake Source Parameters

<p>The use of Distributed Acoustic Sensing (DAS) presents unique advantages for earthquake monitoring compared with standard seismic networks: spatially dense measurements adapted for harsh environments and designed for remote operation. However, the ability to determine earthquake source parameters using DAS is yet to be fully established. In particular, resolving the magnitude and stress drop, is a fundamental objective for seismic monitoring and earthquake early warning. To apply existing methods for source parameter estimation to DAS signals, they must first be converted from strain to ground motions. This conversion can be achieved using the waves’ apparent phase velocity, which varies for different seismic phases ranging from fast body-waves to slow surface- and scattered-waves. To facilitate this conversion and improve its reliability, an algorithm for slowness determination is presented, based on the local slant-stack transform. This approach yields a unique slowness value at each time instance of a DAS time-series. The ability to convert strain-rate signals to ground accelerations is validated using simulated data and applied to several earthquakes recorded by dark fibers of three ocean-bottom telecommunication cables in the Mediterranean Sea. The conversion emphasizes fast body-waves compared to slow scattered-waves and ambient noise, and is robust even in the presence of correlated noise and varying wave propagation directions. Good agreement is found between source parameters determined using converted DAS waveforms and on-land seismometers for both P- and S-wave records. The demonstrated ability to resolve source parameters using P-waves on horizontal ocean-bottom fibers is key for the implementation of DAS based earthquake early warning, which will significantly improve hazard mitigation capabilities for offshore and tsunami earthquakes.</p>

A teleseismic body-wave analysis of the May 1980 Mammoth Lakes, California, earthquakes

1983 ◽  
Vol 73 (2) ◽  
pp. 419-434
Author(s):  
Jeffery S. Barker ◽  
Charles A. Langston
Keyword(s):  
Body Wave ◽  
Moment Tensor ◽  
Normal Fault ◽  
Strike Slip ◽  
Body Waves ◽  
P Wave ◽  
Moment Tensors ◽  
Double Couple ◽  
The Moment ◽  
Mammoth Lakes

abstract Teleseismic P-wave first motions for the M ≧ 6 earthquakes near Mammoth Lakes, California, are inconsistent with the vertical strike-slip mechanisms determined from local and regional P-wave first motions. Combining these data sets allows three possible mechanisms: a north-striking, east-dipping strike-slip fault; a NE-striking oblique fault; and a NNW-striking normal fault. Inversion of long-period teleseismic P and SH waves for the events of 25 May 1980 (1633 UTC) and 27 May 1980 (1450 UTC) yields moment tensors with large non-double-couple components. The moment tensor for the first event may be decomposed into a major double couple with strike = 18°, dip = 61°, and rake = −15°, and a minor double couple with strike = 303°, dip = 43°, and rake = 224°. A similar decomposition for the last event yields strike = 25°, dip = 65°, rake = −6°, and strike = 312°, dip = 37°, and rake = 232°. Although the inversions were performed on only a few teleseismic body waves, the radiation patterns of the moment tensors are consistent with most of the P-wave first motion polarities at local, regional, and teleseismic distances. The stress axes inferred from the moment tensors are consistent with N65°E extension determined by geodetic measurements by Savage et al. (1981). Seismic moments computed from the moment tensors are 1.87 × 1025 dyne-cm for the 25 May 1980 (1633 UTC) event and 1.03 × 1025 dyne-cm for the 27 May 1980 (1450 UTC) event. The non-double-couple aspect of the moment tensors and the inability to obtain a convergent solution for the 25 May 1980 (1944 UTC) event may indicate that the assumptions of a point source and plane-layered structure implicit in the moment tensor inversion are not entirely valid for the Mammoth Lakes earthquakes.

Source Parameter Sensitivity of Earthquake Simulations assisted by Machine Learning 

2021 ◽  
Author(s):  
Marisol Monterrubio-Velasco ◽  
J. Carlos Carrasco-Jimenez ◽  
Otilio Rojas ◽  
Juan E. Rodriguez ◽  
David Modesto ◽  
...  
Keyword(s):  
Machine Learning ◽  
High Performance ◽  
Moment Tensor ◽  
Source Parameters ◽  
Velocity Model ◽  
Source Parameter ◽  
Earthquake Simulation ◽  
Centroid Moment Tensor ◽  
Ground Shaking ◽  
Earthquake Simulations

<p>After large magnitude earthquakes have been recorded, a crucial task for hazard assessment is to quickly estimate Ground Shaking (GS) intensities at the affected region. Urgent physics-based earthquake simulations using High-Performance Computing (HPC) facilities may allow fast GS intensity analyses but are very sensitive to source parameter values. When using fast estimates of source parameters such as magnitude, location, fault dimensions, and/or Centroid Moment Tensor (CMT), simulations are prone to errors in their computed GS. Although the approaches to estimate earthquake location and magnitude are consolidated, depth location estimates are largely uncertain. Moreover, automatic CMT solutions are not always provided by seismological agencies, or such solutions are available at later times after waveform inversions allow the determination of moment tensor components. The uncertainty on these parameters, especially a few minutes after the earthquake has been registered, strongly affects GS maps resulting from simulations.</p><p>In this work, we present a workflow prototype to produce an uncertainty quantification method as a function of the source parameters. The core of this workflow is based on Machine Learning (ML) techniques. As a study case, we consider a domain of 110x80 km centered in 63.9ºN-20.6ºW in Southern Iceland, where the 17 best-mapped faults have hosted the historical events of the largest magnitude. We generate synthetic GS intensity maps using the AWP-ODC finite-difference code for earthquake simulation and a one-dimensional velocity model, with 40 recording surface stations. By varying a few source parameters (e.g. event magnitude, CMT, and hypocenter location), we finally model tens of thousands of hypothetical earthquakes. Our ML analog will then be able to relate GS intensity maps to source parameters, thus simplifying sensitivity studies.</p><p>Additionally, the results of this workflow prototype will allow us to obtain ML-based intensity maps a few seconds after an earthquake occurs exploiting the predictive power of ML techniques. We will evaluate the accuracy of these maps as standalone complements to GMPEs and simulations.</p>

scholarly journals Source Parameter of Earthquakes in Talala, Gujarat (India): An Implication towards Seismotectonic

Proceedings ◽  
2019 ◽  
Vol 24 (1) ◽  
pp. 7
Author(s):  
Sandeep Kumar Aggarwal
Keyword(s):  
Epicentral Distance ◽  
Moment Tensor ◽  
Source Parameters ◽  
Focal Depth ◽  
B Value ◽  
Complete Sequence ◽  
P Value ◽  
Centroid Moment Tensor ◽  
North East ◽  
Lateral Plane

Talala is an excellent example of triggered neo-tectonic seismicity between two dams during a monsoon. An earthquake of Mmax 5.1 on 6 November 2007 at 21.16° N; 70.54° E, with a focal depth of 4.5 km and complete sequence, was first-time recorded on the latest broadband sensor. This found a dam/monsoon-induced earthquake preceded by 18 foreshocks of 2 ≤ Mw ≤ 4.8 within 9 h 11 minute, as well as smaller shocks that may not have been recorded because of sparse network coverage. After the deployment of local mobile observatories, aftershocks of Mw ≥ 1.0, which continued for months and subsided to background seismicity after four months, were recorded. The same kind of phenomena repeated, with Mmax 5.0 on 20 October 2011 at 21.06° N; 70.50° E, focal depth 5.5 km, which implies that the potential to generate dam/monsoon-induced seismicity took nearly four years again. These phenomena continued and the sequence was recorded by a network of 10 broadband seismographs (three in the Talala area and seven at an epicentral distance of 30 to 300 km). Centroid Moment Tensor (CMT) solutions and spectral source parameters of mainshock and aftershocks are evaluated to understand the seismotectonic of the region. The CMT depicts a major strike-slip motion along East North East-West South West with a left-lateral plane at 4.5 km depth. This indicates a sympathetic fault extension of the Son-Narmada fault. The source parameters of 400 shocks of Mw 1.0 to 5.1 found seismic moment 1011 to 1016.5 N-m, source radii 120–850 meter, and a stress drop of 0.003 to 25.43 Mpa. The b-value, p-value, fractal dimension, and slip on estimated different faults. The comparison between Talala and Koyna dam-induced source parameters tries to establish a comparison of seismicity from different parts of the world.

scholarly journals Identifikasi Sesar di Wilayah Gorontalo dengan Analisis Mekanisme Bola Fokus

Jurnal MIPA ◽  
2014 ◽  
Vol 3 (1) ◽  
pp. 40
Author(s):  
Nurfitriani . ◽  
Guntur Pasau ◽  
Slamet Suyitno Raharjo
Keyword(s):  
Focal Mechanism ◽  
Active Fault ◽  
Moment Tensor ◽  
Earthquake Catalog ◽  
Centroid Moment Tensor ◽  
Geological Map ◽  
Fault Structures

Gorontalo menjadi salah satu daerah rawan bencana gempa bumi dan ecara tektonik berada di wilayah pertemuan 2 lempeng besar, yakni lempeng Pasifik dan Eurasia serta lempeng-lempeng mikro. Peta Geologi Gorontalo menunjukkan adanya struktur sesar yang memotong wilayah kota Gorontalo. Adapun tujuan penelitian ini adalah mengidentifikasi keberadaan struktur sesar di wilayah Gorontalo dengan menggunakan metode mekanisme bola fokus kejadian gempa bumi di wilayah daratan Gorontalo periode 1963-2013 dengan sumber data dari katalog gempa bumi USGS, Global Centroid Momen Tensor, dan BMKG. Analisis bola fokus menunjukkan adanya 3 daerah dugaan sesar aktif, dengan tipe sesar cenderung oblique, dengan panjang 24,54 km sampai 27,54 km dan lebar rupture 8,51 km sampai 9,22 km. Hasil analisis ini juga mendeteksi adanya satu daerah dugaan sesar aktif yang tidak teridentifikasi pada peta geologi.Gorontalo is one of the earthquake prone areas and is tectonically located at the junction of two major plates and some microplates. Geological map indicated the presence of fault structures across Gorontalo. This study was aimed to identify the presence of fault structures in the Gorontalo area using focal mechanism of earthquakes in the mainland region of Gorontalo at the period of 1963-2013 with data sourced from the USGS earthquake catalog, the Global Centroid Moment Tensor, and BMKG. The analysis showed that there were 3 suspected active fault area having oblique-type fault with length of 24,54 to 27,54 km and rupture width of 8,51 to 9,22 km. The analysis also detected the presence of a suspected active fault area which was not identified on the geological map.

scholarly journals NEAR REAL-TIME DETERMINATION OF EARTHQUAKE SOURCE PARAMETERS FOR TSUNAMI EARLY WARNING FROM GEODETIC OBSERVATIONS

2016 ◽  
Vol XLI-B8 ◽  
pp. 117-120
Author(s):  
Sunanda Manneela ◽  
T. Srinivasa Kumar ◽  
Shailesh R. Nayak
Keyword(s):  
Real Time ◽  
Early Warning ◽  
Rapid Determination ◽  
Moment Tensor ◽  
Source Parameters ◽  
Critical Role ◽  
Tsunami Source ◽  
Tsunami Early Warning ◽  
Earthquake Source Parameters

Exemplifying the tsunami source immediately after an earthquake is the most critical component of tsunami early warning, as not every earthquake generates a tsunami. After a major under sea earthquake, it is very important to determine whether or not it has actually triggered the deadly wave. The near real-time observations from near field networks such as strong motion and Global Positioning System (GPS) allows rapid determination of fault geometry. Here we present a complete processing chain of Indian Tsunami Early Warning System (ITEWS), starting from acquisition of geodetic raw data, processing, inversion and simulating the situation as it would be at warning center during any major earthquake. We determine the earthquake moment magnitude and generate the centroid moment tensor solution using a novel approach which are the key elements for tsunami early warning. Though the well established seismic monitoring network, numerical modeling and dissemination system are currently capable to provide tsunami warnings to most of the countries in and around the Indian Ocean, the study highlights the critical role of geodetic observations in determination of tsunami source for high-quality forecasting.

Quick determination of earthquake source parameters from GPS measurements: a study of suitability for Taiwan

2019 ◽  
Vol 219 (2) ◽  
pp. 1148-1162
Author(s):  
Jiun-Ting Lin ◽  
Wu-Lung Chang ◽  
Diego Melgar ◽  
Amanda Thomas ◽  
Chi-Yu Chiu
Keyword(s):  
Rapid Determination ◽  
Moment Tensor ◽  
Near Field ◽  
Source Parameters ◽  
Early Warning Systems ◽  
Earthquake Magnitude ◽  
Observation System ◽  
Earthquake Source Parameters ◽  
Finite Fault

SUMMARY We test the feasibility of GPS-based rapid centroid moment tensor (GPS CMT) methods for Taiwan, one of the most earthquake prone areas in the world. In recent years, Taiwan has become a leading developer of seismometer-based earthquake early warning systems, which have successfully been applied to several large events. The rapid determination of earthquake magnitude and focal mechanism, important for a number of rapid response applications, including tsunami warning, is still challenging because of the limitations of near-field inertial recordings. This instrumental issue can be solved by an entirely different observation system: a GPS network. Taiwan is well posed to take advantage of GPS because in the last decade it has developed a very dense network. Thus, in this research, we explore the suitability of the GPS CMT inversion for Taiwan. We retrospectively investigate six moderate to large (Mw6.0 ∼ 7.0) earthquakes and propose a resolution test for our model, we find that the minimum resolvable earthquake magnitude of this system is ∼Mw5.5 (at 5 km depth). Our tests also suggest that the finite fault complexity, often challenging for the near-field methodology, can be ignored under such good station coverage and thus, can provide a fast and robust solution for large earthquake directly from the near field. Our findings help to understand and quantify how the proposed methodology could be implemented in real time and what its contributions could be to the overall earthquake monitoring system.

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