Relocation of aftershocks, focal mechanisms and stress inversion: Implications toward the seismo-tectonics of the causative fault zone of Mw7.6 2001 Bhuj earthquake (India)

2007 ◽  
Vol 429 (1-2) ◽  
pp. 61-78 ◽  
Author(s):  
P. Mandal ◽  
S. Horton
Keyword(s):  
Fault Zone ◽  
Focal Mechanisms ◽  
Bhuj Earthquake ◽  
Stress Inversion

A methodology for unstructured damped stress inversion of microseismic focal mechanisms: Application to the Vaca Muerta Formation, Argentina

Geophysics ◽  
2020 ◽  
Vol 85 (2) ◽  
pp. KS39-KS50
Author(s):  
Bing Q. Li ◽  
Jing Du
Keyword(s):  
Stress State ◽  
Unstructured Grid ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Instability Criterion ◽  
Regular Grid ◽  
Stress Inversion ◽  
Stress Regime ◽  
Vaca Muerta ◽  
Vaca Muerta Formation

Current methodologies for stress inversion from microseismic focal mechanisms require the assignment of events to a regular grid and then solving for the stress state at each grid node. This approach can lead to irregularities in the solution because some nodes may contain few or even no events. To address this issue, we modified the algorithm to solve for stresses on an irregular (unstructured) grid. We first use the [Formula: see text]-means algorithm to split the data into suitably sized groups. The centroids of these groups are then considered as the nodes of an unstructured grid, and we simultaneously solve for the stress state in each group using damped inversion. To account for the irregularity of the unstructured grid, we use the reciprocal square distance between nodes as weights, as opposed to the existing method in which a weight of unity is assigned between adjacent nodes on a regular grid. Focal planes are selected from the auxiliary plane using the fault instability criterion. The method is first applied to synthetic data sets in which we simulate and subsequently invert for the stress field around a mode-I fracture at depth, in a strike-slip and in a normal faulting stress regime. Results indicate a stress orientation error of 10° and a stress ratio error between 1% and 10%. We then consider focal mechanism data from an unconventional shale play in the Vaca Muerta Formation in Argentina, and our results suggest the presence of a preexisting strike-slip faulting stress regime. We also find that the unambiguous focal plane picks suggest that the apparent dip-slip focal mechanisms are indeed dip-slip movement along subvertical natural fractures, which correlate well with image log data. We suggest that these dip-slip events are caused by stress changes induced by the opening of the hydraulic fractures.

Seismotectonics of the Ionian-Akarnania Block (IAB) and Western Greece deduced from a local seismic deployment.

2020 ◽  
Author(s):  
Antoine Haddad ◽  
Athanassios Ganas ◽  
Ioannis Kassaras ◽  
Matteo Lupi
Keyword(s):  
Fault Zone ◽  
Velocity Model ◽  
Focal Mechanisms ◽  
Seismogenic Zone ◽  
The South ◽  
S Wave ◽  
North West ◽  
The North ◽  
Short Period ◽  
Western Greece

<p>From July 2016 to May 2017, we deployed a local seismic network composed of 15 short-period seismic stations to investigate the ongoing seismotectonic deformation of Western Greece with emphasis on the region between Ambrakikos Gulf (to the north) and Kyparissia (to the south). The network was deployed to investigate the behavior of key crustal blocks in western Greece, such as the Ionian-Akarnania Block (IAB).</p><p>After applying automatic P- and S- wave phase picking we located 1200 local earthquakes using HypoInverse and constrained five 1D velocity model by applying the error minimization technique. Events were relocated using HypoDD and 76  focal mechanisms were computed for events with magnitudes down to M<sub>L</sub> 2.3 using first motion polarities.</p><p>We combined the calculated focal mechanisms and the relocated seismicity to shed light on the IAB block boundaries. Three boundaries highlighted by previous studies were also evidenced :</p><p>-The north-west margin of the block, the Cephalonia Transform Fault, Europe‘s most active fault. NW-striking dextral strike-slip motion was recognized for this fault near the Gulf of Myrtos and the town of Fiskardo.</p><p>- The south-east margin is the Movri-Amaliada right-lateral Fault Zone, activated during the Movri Mt. M<sub>w</sub> 6.4 earthquake sequence.</p><p>- The Ambrakikos Gulf (a young E-W rift) and the NW-striking left-lateral Katouna-Stamna Fault zone depict the north and north-eastern margins of the IAB block.</p><p>Seismicity lineaments and focal mechanisms define theKyllini-Cephalonia left-lateral fault, which is also highlighted by bathymetry data. We interpret this fault as the south-western margin of IAB separating an aseismic area observed between Cephalonia and Akarnania from a seismogenic zone north of Zakynthos Island and bridging NW Peloponnese with Cephalonia.</p>

scholarly journals Sensitivity of stress inversion of focal mechanisms to pore pressure changes

2016 ◽  
Vol 43 (16) ◽  
pp. 8441-8450 ◽  
Author(s):  
Patricia Martínez‐Garzón ◽  
Václav Vavryčuk ◽  
Grzegorz Kwiatek ◽  
Marco Bohnhoff
Keyword(s):  
Pore Pressure ◽  
Focal Mechanisms ◽  
Stress Inversion ◽  
Pressure Changes

Seismogenic Structures in the Ma River Fault Zone, Vietnam: Insights from Focal Mechanisms of Microearthquakes and Local Stress States

2018 ◽  
Vol 108 (6) ◽  
pp. 3260-3269
Author(s):  
Wei‐Jhe Wu ◽  
Strong Wen ◽  
Chi‐Cha Tang ◽  
Yu‐Lien Yeh ◽  
Hop Phong Lai ◽  
...  
Keyword(s):  
Fault Zone ◽  
Local Stress ◽  
Focal Mechanisms ◽  
Seismogenic Structures ◽  
Stress States

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.

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