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.

Focal Mechanisms of West Bohemia, Central Europe, Earthquakes—End of May 2014: Evidence of Volume Changes

2021 ◽  
Author(s):  
Dana Křížová ◽  
Jiří Málek
Keyword(s):  
Central Europe ◽  
Moment Tensor ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Earthquake Swarms ◽  
Quaternary Volcanism ◽  
Moment Tensors ◽  
Isotropic Part ◽  
West Bohemia ◽  
Source Mechanisms

Abstract West Bohemia is a region with a lot of mineral springs and gas outflows, which seems to be related to the remains of Quaternary volcanism in Central Europe. Earthquake swarms in shallow depths (less than 15 km) are very frequent there. We focused on the strongest earthquake over the past 30 yr (31 May, 2014 Mw∼3.8) and on two smaller ones (Mw∼2.9 and 2.5) from the same day. Seismograms from local and regional seismic stations were used to calculate the full and deviatoric moment tensors using low-frequency full-waveform inversion. The studied events have similar source mechanisms. The aforementioned earthquake sequence was selected to observe the isotropic part (negative value = implosion) of full moment tensors. It could relate to the motion and phase transition of fluids, especially water, and CO2. The main goal of this study is to contribute to clarification of the nature of earthquake swarms in the western edge of the Bohemian Massif. Negative value of the isotropic part of full moment tensor could be related to the closing of cracks and fissures during a rupture process.

scholarly journals Seismic moment tensors from synthetic rotational and translational ground motion: Green’s functions in 1-D versus 3-D

2020 ◽  
Vol 223 (1) ◽  
pp. 161-179
Author(s):  
S Donner ◽  
M Mustać ◽  
B Hejrani ◽  
H Tkalčić ◽  
H Igel
Keyword(s):  
Ground Motion ◽  
Seismic Moment ◽  
Structural Model ◽  
Moment Tensor ◽  
Waveform Inversion ◽  
Seismic Moment Tensor ◽  
Tectonic Event ◽  
Moment Tensors ◽  
Rotational Ground Motion ◽  
D Model

SUMMARY Seismic moment tensors are an important tool and input variable for many studies in the geosciences. The theory behind the determination of moment tensors is well established. They are routinely and (semi-) automatically calculated on a global scale. However, on regional and local scales, there are still several difficulties hampering the reliable retrieval of the full seismic moment tensor. In an earlier study, we showed that the waveform inversion for seismic moment tensors can benefit significantly when incorporating rotational ground motion in addition to the commonly used translational ground motion. In this study, we test, what is the best processing strategy with respect to the resolvability of the seismic moment tensor components: inverting three-component data with Green’s functions (GFs) based on a 3-D structural model, six-component data with GFs based on a 1-D model, or unleashing the full force of six-component data and GFs based on a 3-D model? As a reference case, we use the inversion based on three-component data and 1-D structure, which has been the most common practice in waveform inversion for moment tensors so far. Building on the same Bayesian approach as in our previous study, we invert synthetic waveforms for two test cases from the Korean Peninsula: one is the 2013 nuclear test of the Democratic People’s Republic of Korea and the other is an Mw  5.4 tectonic event of 2016 in the Republic of Korea using waveform data recorded on stations in Korea, China and Japan. For the Korean Peninsula, a very detailed 3-D velocity model is available. We show that for the tectonic event both, the 3-D structural model and the rotational ground motion, contribute strongly to the improved resolution of the seismic moment tensor. The higher the frequencies used for inversion, the higher is the influence of rotational ground motions. This is an important effect to consider when inverting waveforms from smaller magnitude events. The explosive source benefits more from the 3-D structural model than from the rotational ground motion. Nevertheless, the rotational ground motion can help to better constraint the isotropic part of the source in the higher frequency range.

scholarly journals A focal mechanism catalogue of earthquakes that occurred in the southeastern Alps and surrounding areas from 1928–2019

2021 ◽  
Vol 13 (5) ◽  
pp. 2245-2258
Author(s):  
Angela Saraò ◽  
Monica Sugan ◽  
Gianni Bressan ◽  
Gianfranco Renner ◽  
Andrea Restivo
Keyword(s):  
Focal Mechanism ◽  
Moment Tensor ◽  
Active Regions ◽  
Focal Mechanisms ◽  
Seismic Moment Tensor ◽  
Fault Plane Solutions ◽  
First Arrival ◽  
Populated Region ◽  
Surrounding Areas ◽  
Catalogue Of Earthquakes

Abstract. We present a focal mechanism catalogue of earthquakes that occurred in the southeastern Alps and surrounding areas from 1928 to 2019. The area involved in the process of convergence between the Adria microplate and Eurasia is one of the most seismically active regions in the Alpine Belt. The seismicity is minor, with the Ms= 6.5 Friuli earthquake being the strongest event recorded in the area, but the seismic risk is relevant because it is a highly populated region. For this reason, numerous studies have been carried out over time to investigate the stress field and the geodynamic characteristics of the region using focal mechanisms. To provide a comprehensive set of revised information, which is challenging to build quickly because the data are dispersed over many papers, we collected and revised the focal mechanisms that were previously published in the literature. Additionally, depending on the data quality and availability, we computed new focal mechanisms by first arrival polarity inversion or seismic moment tensor. Finally, we merged all the fault plane solutions to obtain a catalogue for a selection of 772 earthquakes with 1.8≤M≤6.5. For each earthquake, we reported all the available focal mechanisms obtained by different authors. We also suggested a preferred solution for users who need information provided expeditiously. The catalogue (https://doi.org/10.5281/zenodo.4660412; Saraò et al., 2021) is given as the Supplement of this paper and will be updated periodically (https://doi.org/10.5281/zenodo.4284970).

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>

New insight into the 24 January 2020, Mw 6.8 Elazığ earthquake (Turkey): An evidence for rupture-parallel pull-apart basin activation along the East Anatolian Fault Zone constrained by Geodetic and Seismological data

2021 ◽  
Vol 64 (4) ◽  
pp. SE439
Author(s):  
T Serkan Irmak ◽  
Mustafa Toker ◽  
Evrim Yavuz ◽  
Erman Şentürk ◽  
Muhammed Ali Güvenaltın
Keyword(s):  
Fault Zone ◽  
Surface Deformation ◽  
Waveform Inversion ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Deformation Pattern ◽  
Pull Apart Basin ◽  
Insight Into ◽  
East Anatolian Fault Zone ◽  
East Anatolian Fault

In this study, we investigated the main features of the causative fault of the 24 January 2020, Mw 6.8 Elazığ earthquake (Turkey) using seismological and geodetic data sets to provide new insight into the East Anatolian Fault Zone (EAFZ). We first constrained the co-seismic surface deformation and the rupture geometry of the causative fault segment using Interferometric Synthetic Aperture Radar (InSAR) interferograms (Sentinel-1A/B satellites) and teleseismic waveform inversion, respectively. Also, we determined the centroid moment tensor (CMT) solutions of focal mechanisms of the 27 aftershocks using the regional waveform inversion method. Finally, we evaluated the co-seismic slip distribution and the CMT solutions of the causative fault as well as of adjacent segments using the 27 focal solutions of the aftershocks, superimposed on the surface deformation pattern. The CMT solution of the 24 January 2020Elazığ earthquake reveals a pure strike-slip focal mechanism, consistent with the structural pattern and left-lateral motion of the EAFZ. The rupture process of the Elazığ event indicated that the rupture is started at 12 km around the hypocenter, and then propagated bilaterally along the NE-SW but mainly toward the southwest. The rupture slip has initially propagated toward the southwest (first 10 s) and northeast (4 s), and again toward the southwest (9 s). Maximum displacement is calculated as 1.3 m about 20 km southwest of the hypocenter at 6 km depth (centroid depth). The rupture stopped to down-dip around 20 km depth toward the southwest. The distribution of the slip vectors indicates that the rupture continued mostly through a normal oblique movement. Most of the moment release was released SW of the hypocenter and the rupture reached up to around 50 km. The focal mechanisms of analyzed 27 aftershocks show strike-slip, but mostly normal and normal oblique-slip faulting with an orientation of the tensional axes (NNE-SSW), indicating a normal oblique-slip, “transtensional” stress regime, parallel-subparallel to the strike of the EAFZ, consistent with SW-rupture directivity and co- seismic deformation pattern. Finally, based on the co-seismic surface deformation compatible with the distributional pattern of normal focal solutions, normal and normal oblique-slip focals of the aftershocks evidence the rupture-parallel pull-apart basin activation as a segment boundary of the left-lateral strike-slip movement of the EAFZ.

scholarly journals RECENT SEISMIC ACTIVITY IN CENTRAL GREECE REVEALING LOCAL SEISMOTECTONIC PROPERTIES

2017 ◽  
Vol 43 (4) ◽  
pp. 2075
Author(s):  
Ch. K. Karamanos ◽  
V. G. Karakostas ◽  
L. Seeber ◽  
E. E. Papadimitriou ◽  
A.A. Kilias
Keyword(s):  
Fault Zone ◽  
Fault Plane ◽  
Focal Mechanisms ◽  
Normal Faulting ◽  
Seismic Excitations ◽  
Lateral Component ◽  
Fault Plane Solutions ◽  
Central Greece ◽  
Source Characteristics ◽  
The Town

The December 2008, M=5.2 earthquake occurred in the Voiotikos–Kifissos basin near the town of Amfikleia in Central Greece and was followed by an intense sequence with hundreds of earthquakes. Mainshock source characteristics derived from the recordings of the Greek National Seismological Network are consistent with previous known earthquakes as well as with the current nearly N–S extensional regime. The adequate azimuthal coverage and the calculated time residuals at each seismological station ensure high location accuracy, whereas the stations operated close to the seismic excitations constrained 80% of the focal depths between 8 and 12km. Distances from the mainshock epicenter to the 10 closest seismological stations vary from 15 to 75 km. Hypoinverse and HypoDD were used for locations, and FPFIT was used for fault plane solutions of events with an adequate number of clear first arrivals. The hypocenters and focal mechanisms illuminate a ≈10km–long fault zone striking nearly E–W with oblique normal faulting and a small left lateral component. The Voiotikos–Kifissos basin is bordered in the south by two left–stepping en echelon segments known as the Pavliani fault zone and the Parnassos detachment, which strike NW and dip NE. In our preferred interpretation, the Amfikleia mainshock ruptured a previously recognized south–dipping fault antithetic to the basin border faults. This fault may be associated with the left step on the border fault, which would be releasing if that fault had a sinistral component.

scholarly journals Fault-plane solutions from moment-tensor inversion and preliminary Coulomb stress analysis for the Emilia Plain

2012 ◽  
Vol 55 (4) ◽  
Author(s):  
Angela Saraò ◽  
Laura Peruzza
Keyword(s):  
Elastic Stress ◽  
Fault Plane ◽  
Moment Tensor ◽  
Focal Mechanisms ◽  
Structural System ◽  
Fault Plane Solutions ◽  
Stress Changes ◽  
Intermediate Distance ◽  
Complex Structural ◽  
Coulomb Stress Analysis

<p>We investigate the seismicity occurred in the Po area, in the period July 2011-June 1012, by means of moment tensor and we use our set of revised focal mechanisms - computed for M&gt; 3.7 earthquakes - to evaluate Coulomb elastic stress changes in order to detect potential intermediate-distance faults interaction, and the main features of this complex structural system.</p>

Seismic Source Processes of 25 Earthquakes (Mw>5) in the Gulf of California

2022 ◽  
Author(s):  
Eduardo Huesca-Pérez ◽  
Edahí Gutierrez-Reyes ◽  
Luis Quintanar
Keyword(s):  
Gulf Of California ◽  
Moment Tensor ◽  
Source Parameters ◽  
Seismic Source ◽  
Focal Mechanisms ◽  
Process Models ◽  
Moment Tensors ◽  
Time Space ◽  
Double Couple ◽  
Broadband Seismograms

ABSTRACT The Gulf of California (GoC) is a complex tectonic boundary that has been instrumented in the past several decades to record broadband seismograms. This volume of data has allowed us to study several source parameters systematically. Before, only a few source parameters of earthquakes greater than magnitude five had been studied in the GoC area. We re-examined the focal mechanisms of several earthquakes in the southern GoC that occurred over the last 20 yr using local–regional distance broadband seismograms. These focal mechanisms were then used as input data to retrieve the time–space history of the rupture for each earthquake. This work contributes to the study of 25 rupture-process models computed with the method proposed by Yagi et al. (1999). To investigate more about the nature of the seismicity in the GoC, we also calculated the non-double-couple component of moment tensors for 45 earthquakes. Previous studies (e.g., Ortega et al., 2013, 2016) have shown that non-double-couple components from moment tensors in this region are associated with complex faulting, suggesting that oblique faults or several parallel faults are interacting simultaneously. Our results show that, at least for moderate earthquakes (5 &lt; M &lt; 6), rupture processes in the GoC show a complex interaction between fault systems. It is revealed on the important contribution of non-double-couple component obtained in the full moment tensor analysis.

Focal mechanisms of the 2017 North Korean nuclear test and its early collapse event

2019 ◽  
Vol 220 (2) ◽  
pp. 737-752 ◽  
Author(s):  
Henglei Xu ◽  
Sidao Ni ◽  
Wenxue Liu ◽  
Haofeng Zhu ◽  
Xuliang Wang
Keyword(s):  
Surface Wave ◽  
Wave Amplitude ◽  
Amplitude Ratio ◽  
Moment Tensor ◽  
Waveform Inversion ◽  
Focal Mechanisms ◽  
Nuclear Test ◽  
Quality Data ◽  
Waveform Data ◽  
Event Identification

SUMMARY North Korea conducted sixth underground nuclear test on 3 September 2017. Unlike its previous tests, a rare subsequent collapse event occurred after about 8.5 min. As two types of distinctive shallow seismic events, accurate inversion of their focal mechanisms is important for event identification for CTBT. In this paper, we carry out moment tensor inversion of the nuclear test and the collapse event with gCAP using waveform data from dense regional seismic stations. And their focal mechanisms are further constrained with surface wave amplitude ratio. The results show that the surface wave amplitude ratio has further constraints for screening the waveform inversion results. The resolution of the focal mechanism inversion for the nuclear test is high, which is close to a Crack source. However, the resolution for the collapse event inversion is not so high and the source type is difficult to be accurately determined. One reason of the poor resolution for the collapse event may be due to the limited availability of high quality data, and complexity of the source process might be another factor.

scholarly journals A focal mechanism catalogue of earthquakes that occurred in the southeastern Alps and surrounding areas from 1928–2019

2021 ◽  
Author(s):  
Angela Saraò ◽  
Monica Sugan ◽  
Gianni Bressan ◽  
Gianfranco Renner ◽  
Andrea Restivo
Keyword(s):  
Focal Mechanism ◽  
Moment Tensor ◽  
Active Regions ◽  
Focal Mechanisms ◽  
Seismic Moment Tensor ◽  
Fault Plane Solutions ◽  
First Arrival ◽  
Populated Region ◽  
Surrounding Areas ◽  
Catalogue Of Earthquakes

Abstract. We present a focal mechanism catalogue of earthquakes that occurred in the southeastern Alps and surrounding areas from 1928 to 2019. The area involved in the process of convergence between the Adria microplate and Eurasia is one of the most seismically active regions in the Alpine Belt. The seismicity is minor, with the Ms =thinsp;6.5 Friuli earthquake being the strongest event recorded in the area, but the seismic hazard is relevant because it is a highly populated region. For this reason, numerous studies have been carried out over time to investigate the stress field and the geodynamic characteristics of the region using focal mechanisms. To provide a comprehensive set of revised information, which is challenging to build quickly because the data is dispersed over many papers, we collected and revised the focal mechanisms that were previously published in the literature. Additionally, depending on the data quality and availability, we computed new focal mechanisms by first arrival polarity inversion or seismic moment tensor. Finally, we merged all the fault plane solutions to obtain a catalogue for a selection of 772 earthquakes with 1.8thinsp;≤thinsp;Mthinsp;≤thinsp;6.5. For each earthquake, we reported all the available focal mechanisms obtained by different authors. However, we also suggested a preferred solution for users who need expeditious information. The catalogue is available at https://doi.org/10.5281/zenodo.4284971 (Saraò et al., 2020).

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