scholarly journals Fault Geometry and Mechanism of the Mw 5.7 Nakchu Earthquake in Tibet Inferred from InSAR Observations and Stress Measurements

2021 ◽  
Vol 13 (24) ◽  
pp. 5142
Author(s):  
Yujiang Li ◽  
Yongsheng Li ◽  
Xingping Hu ◽  
Haoqing Liu
Keyword(s):  
Focal Mechanism ◽  
Historical Earthquakes ◽  
Tectonic Stress ◽  
Indian Plate ◽  
Coseismic Deformation ◽  
Normal Faulting ◽  
Eurasian Plate ◽  
Seismogenic Fault ◽  
Stress Measurements ◽  
Focal Mechanism Solutions

Different types of focal mechanism solutions for the 19 March 2021 Mw 5.7 Nakchu earthquake, Tibet, limit our understanding of this earthquake’s seismogenic mechanism and geodynamic process. In this study, the coseismic deformation field was determined and the geometric parameters of the seismogenic fault were inverted via Interferometric Synthetic Aperture Radar (InSAR) processing of Sentinel-1 data. The inversion results show that the focal mechanism solutions of the Nakchu earthquake are 237°/69°/−70° (strike/dip/rake), indicating that the seismogenic fault is a NEE-trending, NW-dipping fault dominated by the normal faulting with minor sinistral strike-slip components. The regional tectonic stress field derived from the in-situ stress measurements shows that the orientation of maximum principal compressive stress around the epicenter of the Nakchu earthquake is NNE, subparallel to the fault strike, which controlled the dominant normal faulting. The occurrence of seven M ≥ 7.0 historical earthquakes since the M 7.0 Shenza earthquake in 1934 caused a stress increase of 1.16 × 105 Pa at the hypocenter, which significantly advanced the occurrence of the Nakchu earthquake. Based on a comprehensive analysis of stress fields and focal mechanisms of the Nakchu earthquake, we propose that the dominated normal faulting occurs to accommodate the NE-trending compression of the Indian Plate to the Eurasian Plate and the strong historical earthquakes hastened the process. These results provide a theoretical basis for understanding the geometry and mechanics of the seismogenic fault that produced the Nakchu earthquake.

scholarly journals Probabilistic Earthquake Scenarios in Bangladesh Based on Magnitude and Depth Parameters

2019 ◽  
Vol 8 (11) ◽  
pp. 2082-2088
Keyword(s):  
Historical Earthquakes ◽  
Indian Plate ◽  
United States Geological Survey ◽  
Distribution Analysis ◽  
Eurasian Plate ◽  
Historical Evidence ◽  
Earthquake Scenarios ◽  
Prime Concern ◽  
Tectonic Settings ◽  
Populated Region

Geographical and tectonic settings of Bangladesh make it susceptible to seismic hazard. Besides, historical evidence says that numerous earthquakes with very large magnitude occur in this region. Currently, the Indian plate is gradually moving in the northeast and subduce beneath the Eurasian Plate. So, geologist suspects that a terrible earthquake with greater than eight (>8) magnitude is inevitable in this highly populated region. Therefore, assessing the integrated vulnerability of earthquake in this region is a prime concern for most of the geologists. In this paper, we performed a rigorous assessment of the earthquake’s vulnerabilities by analysing the historical earthquakes from the last 118 years (1901-2018) that occurred in Bangladesh and the surrounding regions (20.65° N to 28.00° N latitude and 87.00° E to 93.75° E longitude). Moreover, we also perform probability-based distribution analysis to show the intrinsic relationship among various parameters, especially earthquake magnitude and depth. Here, the necessary data are collected from the USGS (United States Geological Survey).

Study on Seismicity and Its Geodynamic Genesis in Ngari Areas

2020 ◽  
Author(s):  
Guangyin Xu ◽  
Qing Wu ◽  
Suyun Wang
Keyword(s):  
Stress Field ◽  
Focal Mechanism ◽  
Seismic Activity ◽  
Tectonic Stress ◽  
Earthquake Catalogue ◽  
Tectonic Stress Field ◽  
Eurasian Plate ◽  
The North ◽  
East Kunlun ◽  
Tectonic Belt

<p>The Ngari area in Tibet is in the forefront of land-continent collisions. The area is accompanied by the polymerization of plates, forming complex structures such as the Tethys Himalayan pleat belt, the Yarlung Zangbo suture belt, and the Gangdese continental margin magma arc from the south to the north. The multi-period dive collision-inland convergence process, the geological structure is complex and the seismicity is very high. Based on the Chinese historical earthquake catalogue, the China Modern Earthquake Catalogue and the seismic data from the International Seismological Center (ISC), we analyzed the seismic activity, focal mechanism and modern tectonic stress field in the Ngari area, and then analyzed the seismicity and its source of geodynamics. The main conclusions are as follows:(1) The seismic activities in the Ngari area are mainly distributed in the Himalayan tectonic belt, the Bangong-Nujiang tectonic belt, the Alkin-East Kunlun tectonic belt, and some near north-south trending tectonic belts; (2) Earthquakes near the Himalayan tectonic belt is dominated by reverse faulting events. The seismic activity near the Bangong-Nujiang tectonic belt and the Alkin-East Kunlun tectonic belt is dominated by strike-slip earthquakes. Near the north-south extensional tectonic belt, the earthquakes show as the normal faulting events. (3) The main direction of the modern tectonic stress field in the study area is near north-south direction; (4) Seismic activity, focal mechanism and modern tectonic stress field show that the geodynamic source in the Ngari region is from Collision and squeezing the between the Eurasian plate and the Indian Ocean plate.</p>

scholarly journals Complex Shear Partitioning Involving the 6 February 2012 MW 6.7 Negros Earthquake Ground Rupture in Central Philippines

Geosciences ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 460
Author(s):  
Rolly E. Rimando ◽  
Jeremy M. Rimando ◽  
Robjunelieaaa B. Lim
Keyword(s):  
Focal Mechanism ◽  
Subduction Zones ◽  
The Philippines ◽  
Focal Mechanism Solution ◽  
Reverse Fault ◽  
Earthquake Hazards ◽  
Seismogenic Fault ◽  
Coseismic Slip ◽  
Focal Mechanism Solutions ◽  
Complex Shear

A 75 km-long, generally NE-striking ground rupture associated with the 6 February 2012 MW 6.7 (Mb 6.9) Negros earthquake was mapped on the eastern side of Negros Island, Philippines. It closely follows a previously unmapped, pre-existing fault trace along the coast which is marked mostly by terrace-forming scarps. The dominance of vertical separation (west side up) is consistent with a west-dipping reverse fault, as indicated by focal mechanism solutions. The ground rupture map eliminates the ambiguity in the focal mechanism solution regarding the orientation, sense of motion, and location of the seismogenic fault plane, which are indispensable in the assessment of seismic hazards and the nature and distribution of deformation. This study uses the ground rupture map of the 2012 Negros earthquake in sorting out the mechanism of deformation in the Visayas Islands region. The ground rupture’s length is well within the aftershock area while its scarp heights are consistent with an earthquake of its magnitude and nature of movement. The 2012 Negros earthquake rupture’s pattern, scarp types, and offset of man-made structures are similar to those of recent reverse/thrust ground ruptures mapped globally and are distinct from those associated with erosion, landslide, and liquefaction. The onshore coseismic reverse fault of the Negros earthquake, which contradicts a model of coseismic slip on an offshore blind thrust fault by previous workers, represents the first thoroughly mapped ground rupture of its kind in the Philippines. The ground ruptures of the 2012 Negros and 2013 Bohol earthquakes, along with the Philippine Trench and the Philippine Fault Zone (PFZ), represent a complex shear partitioning mechanism in the Visayas Islands region. This departs from the current simple shear partitioning model for the region and is distinct from those for other regions along the PFZ and adjacent subduction zones. This study shows how an appreciation of morphotectonic features can lead to a better understanding of the distribution of deformation and the nature of earthquake hazards.

scholarly journals Implications of 3D Seismic Raytracing on Focal Mechanism Determination

2019 ◽  
Vol 109 (6) ◽  
pp. 2746-2754
Author(s):  
Katharina Newrkla ◽  
Hasbi Ash Shiddiqi ◽  
Annie Elisabeth Jerkins ◽  
Henk Keers ◽  
Lars Ottemöller
Keyword(s):  
Focal Mechanism ◽  
Historical Earthquakes ◽  
Velocity Model ◽  
Waveform Data ◽  
Focal Mechanism Solutions ◽  
Velocity Models ◽  
Maximum Value ◽  
3D Velocity Model ◽  
First Motion

Abstract The purpose of this study is to investigate apparent first‐motion polarities mismatch at teleseismic distances in the determination of focal mechanism. We implement and compare four seismic raytracing algorithms to compute ray paths and travel times in 1D and 3D velocity models. We use the raytracing algorithms to calculate the takeoff angles from the hypocenter of the 24 August 2016 Mw 6.8 Chauk earthquake (depth 90 km) in central Myanmar to the stations BFO, GRFO, KONO, and ESK in Europe using a 3D velocity model of the upper mantle below Asia. The differences in the azimuthal angles calculated in the 1D and 3D velocity models are considerable and have a maximum value of 19.6°. Using the takeoff angles for the 3D velocity model, we are able to resolve an apparent polarity mismatch where these stations move from the dilatational to the compressional quadrant. The polarities of synthetic waveforms change accordingly when we take the takeoff angles corresponding to the 3D model into account. This method has the potential to improve the focal mechanism solutions, especially for historical earthquakes where limited waveform data are available.

Seismicity, earthquake mechanisms, and tectonics along the western coast of North America, from 42°N to 61°N

1974 ◽  
Vol 64 (5) ◽  
pp. 1529-1549 ◽  
Author(s):  
Umesh Chandra
Keyword(s):  
Focal Mechanism ◽  
Puget Sound ◽  
Western Coast ◽  
Spreading Ridge ◽  
Normal Faulting ◽  
Transform Faults ◽  
Focal Mechanism Solutions ◽  
Queen Charlotte Islands ◽  
Gorda Ridge ◽  
Recent Earthquakes

Abstract Seismicity maps of the region are presented for the periods January 1900 to June 1973 and January 1961 to June 1973. Focal mechanism solutions for 24 earthquakes (mb ≧ 5.5) occurring between January 1963 to July 1973 have been determined. Four earthquakes which occurred in the vicinity of the Gorda ridge have a component of normal faulting, thus identifying it as a spreading ridge. However, departure of the trend of the axis of tension, determined in the focal mechanism solutions for these earthquakes, from being perpendicular to the trend of the ridge axis indicates that the tectonics of the Gorda basin is complex. The existence of the Blanco fracture zone and the Queen Charlotte Islands fault as dextral transform faults, east block moving south, is confirmed. Evidences derived from the focal mechanism solutions indicate that the Revere-Dellwood and Sovanco fracture zones are also right-lateral transform faults. The northern extent of the Queen Charlotte Islands fault probably terminates near 54.5°N, 135.2°W or 57.5°N, 136°W. Focal mechanism solutions for an earthquake occurring near Vancouver Islands and another near the Puget Sound region in Washington indicate normal faulting and suggest the presence of a downgoing slab of lithosphere in this region. The interpretation is that the former results from tension caused by the bending of the plate as it dips under the continent and the latter results from tension within the sinking slab. Two recent earthquakes which occurred on July 1 and July 3, 1973 at a latitude of about 58°N, have thrust fault solutions and together with the seismicity data suggest a zone of underthrusting of the lithospheric plate between latitudes 58°N to 59.5°N. The possibility of a third zone of subduction north of latitude 59.5°N between longitudes 139°W to 142°W is indicated.

scholarly journals Directional Statistics, Bayesian Methods of Earthquake Focal Mechanism Estimation, and Their Application to New Zealand Seismicity Data

2021 ◽  
Author(s):  
◽  
David Walsh
Keyword(s):  
New Zealand ◽  
Focal Mechanism ◽  
Seismic Velocity ◽  
Region Of Interest ◽  
Velocity Model ◽  
Tectonic Stress ◽  
Focal Mechanism Solutions ◽  
Earthquake Focal Mechanism ◽  
Leibler Divergence ◽  
Focal Mechanism Estimation

<p>A focal mechanism is a geometrical representation of fault slip during an earthquake. Reliable earthquake focal mechanism solutions are used to assess the tectonic characteristics of a region, and are required as inputs to the problem of estimating tectonic stress. We develop a new probabilistic (Bayesian) method for estimating the distribution of focal mechanism parameters based on seismic wave polarity data. Our approach has the advantage of enabling us to incorporate observational errors, particularly those arising from imperfectly known earthquake locations, allowing exploration of the entire parameter space, and leads to natural point estimates of focal mechanism parameters. We investigate the use of generalised Matrix Fisher distributions for parameterising focal mechanism uncertainties by minimising the Kullback-Leibler divergence. We present here the results of our method in two situations. We first consider the case in which the seismic velocity of the region of interest (described by a velocity model) is presumed to be precisely known, with application to seismic data from the Raukumara Peninsula, New Zealand. We then consider the case in which the velocity model is imperfectly known, with application to data from the Kawerau region, New Zealand. We find that our estimated focal mechanism solutions for the most part are consistent with all available polarity data, and correspond closely to solutions obtained using established methods. Further, the generalised Matrix Fisher distributions we examine provide a good fit to our Bayesian posterior PDF of the focal mechanism parameters, enabling the posterior PDF to be succinctly summarised by reporting the estimated parameters of the fitted distribution.</p>

scholarly journals Directional Statistics, Bayesian Methods of Earthquake Focal Mechanism Estimation, and Their Application to New Zealand Seismicity Data

2021 ◽  
Author(s):  
◽  
David Walsh
Keyword(s):  
New Zealand ◽  
Focal Mechanism ◽  
Seismic Velocity ◽  
Region Of Interest ◽  
Velocity Model ◽  
Tectonic Stress ◽  
Focal Mechanism Solutions ◽  
Earthquake Focal Mechanism ◽  
Leibler Divergence ◽  
Focal Mechanism Estimation

<p>A focal mechanism is a geometrical representation of fault slip during an earthquake. Reliable earthquake focal mechanism solutions are used to assess the tectonic characteristics of a region, and are required as inputs to the problem of estimating tectonic stress. We develop a new probabilistic (Bayesian) method for estimating the distribution of focal mechanism parameters based on seismic wave polarity data. Our approach has the advantage of enabling us to incorporate observational errors, particularly those arising from imperfectly known earthquake locations, allowing exploration of the entire parameter space, and leads to natural point estimates of focal mechanism parameters. We investigate the use of generalised Matrix Fisher distributions for parameterising focal mechanism uncertainties by minimising the Kullback-Leibler divergence. We present here the results of our method in two situations. We first consider the case in which the seismic velocity of the region of interest (described by a velocity model) is presumed to be precisely known, with application to seismic data from the Raukumara Peninsula, New Zealand. We then consider the case in which the velocity model is imperfectly known, with application to data from the Kawerau region, New Zealand. We find that our estimated focal mechanism solutions for the most part are consistent with all available polarity data, and correspond closely to solutions obtained using established methods. Further, the generalised Matrix Fisher distributions we examine provide a good fit to our Bayesian posterior PDF of the focal mechanism parameters, enabling the posterior PDF to be succinctly summarised by reporting the estimated parameters of the fitted distribution.</p>

scholarly journals Interaction Between Historical Earthquakes and the 2021 Mw7.4 Maduo Event and Their Impacts on the Seismic Gap Areas Along the East Kunlun Fault

2021 ◽  
Author(s):  
Peiyu Dong ◽  
Bin Zhao ◽  
Xuejun Qiao
Keyword(s):  
Source Area ◽  
Historical Earthquakes ◽  
Tectonic Stress ◽  
Inhibitory Effect ◽  
Seismic Gap ◽  
Seismogenic Fault ◽  
Qinghai Province ◽  
Coulomb Stress Changes ◽  
Stress Shadow ◽  
Stress Changes

Abstract On May 21, 2021 (UTC time), a Mw7.4 earthquake struck Maduo County, Qinghai Province, China. The rupture of this typical strike-slip event and its aftershocks along the Kunlun-Jiangcuo fault (JCF) propagated approximately 170 km from the epicenter. In this study, we calculated the coseismic and postseismic Coulomb stress changes induced by 14 historical earthquakes and investigated their impacts on the 2021 Maduo source area. We found that the JCF is in the stress shadow of these historical events with a combined ΔCFS range of approximately -0.4 to -0.2 MPa. Since the seismogenic fault of the 1937 event is nearly parallel and close to the JCF, the rupture of the 1937 event had the greatest inhibitory effect on Maduo source area. We hypothesize that the actual loading rate at the depth of the seismogenic layer in the Maduo source area is much higher than the simulated value (0.3 kPa/a). Consequently, the Maduo earthquake still occurred despite the considerable delaying effect of these historical earthquakes (especially the 1937 event). Our findings also indicate that the tectonic stress in the eastern Bayanhar block is still rapidly accumulating and adjusting. Our investigation further reveals the enhanced stress induced by the historical and Maduo events with ΔCFS values of approximately 30~300 kPa and 50~300 kPa on the XDS and the eastern end of the EKF, respectively, not only on the MMS but also at the eastern end of each branch segment of the EKF. Hence, considering the accumulation of tectonic stress, we suggest that the seismic hazard in these two regions has been promoted.

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