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Variations of shear-wave splitting parameters in the source region of the 2023 Türkiye doublet earthquakes

Earthquake Science 2024年第2期37卷 174-187页

作者： Xuelai Cao Lijun Chang Institute of Geophysics China Earthquake AdministrationBeijing 100081China

In this study,the shear-wave splitting parameters of local seismic events from the source regions of the 2023 Türkiye MW7.7 and MW7.6 doublet earthquakes(event 1 and event 2,respectively)were measured from June 1,2022,to April 25,2023,and their spatiotemporal characteristics were analyzed.The results revealed clear spatial and temporal differences.Spatially,the dominant fast-wave polarization direction at each station shows a strong correlation with the direction of the maximum horizontal principal compressive stress,as characterized by focal mechanism solutions of seismic events(MW≥3.5)near the station.The dominant fast-wave polarization direction and the regional stress field also showed a strong correlation with the intermovement of the Arabian Plate,African Plate,and Anatolian Block.Along the Nurdagi-Pazarcik fault zone,the seismic fault of event 1,stations closer to the middle of the fault where the mainshock occurred exhibited notably greater delay times than stations located towards the ends of the fault and far from the mainshock.In addition,the stations located to the east of the Nurdagi-Pazarcik fault and to the north of the Sürgüfault also exhibited large delay times.The spatial distribution of shear-wave splitting parameters obtained from each station indicates that the upper-crust anisotropy in the source area is mainly controlled by the regional stress field,which is closely related to the state of the block motion.During the seismogenic process of the MW7.7 earthquake,more stress accumulated in the middle of the Nurdagi-Pazarcik fault than at either end of the fault.Under the influence of the MW7.7 and MW7.6 events,the stress that accumulated during the seismogenic process of the earthquake doublet may have migrated towards some areas outside the aftershock intensive area after the earthquakes,and the crustal stress and its adjustment range near the outer stations increased significantly.With the exception of two stations with few effective events,all stations showed a consistent change in shear-wa

关键词： Türkiye doublet earthquakes shear-wave splitting upper crustal anisotropy stress field

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A seismological evidence for the northwestward movement of Africa with respect to Iberia from shear-wave splitting

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Geoscience Frontiers 2012年第5期3卷 681-696页

作者： Mohamed K.Salah Geology Department Faculty of Science Tanta UniversityTanta 31527Egypt

Seismic anisotropy and its main features along the convergent boundary between Africa and Iberia are detected through the analysis of teleseismic shear-wave splitting. waveform data generated by 95 teleseismic events recorded at 17 broadband stations deployed in the western Mediterranean region are used in the present study. Although the station coverage is not uniform in the Iberian Peninsula and north- west Africa, significant variations in the fast polarization directions and delay times are observed at stations located at different tectonic domains. Fast polarization directions are oriented predominantly NW-SE at most stations which are close to the plate boundary and in central Iberia; being consistent with the absolute plate motion in the region. In the northern part of the Iberian Peninsula, fast velocity direc- tions are oriented nearly E--W; coincident with previous results. Few stations located slightly north of the plate boundary and to the southeast of lberia show E--W to NE-SW fast velocity directions, which may be related to the Alpine Orogeny and the extension direction in lberia. Delay times vary significantly between 0.2 and 1.9 s for individual measurements, reflecting a highly anisotropic structure beneath the recording stations. The relative motion between Africa and lberia represents the main reason for the observed NW-SE orientations of the fast velocity directions. However, different causes of anisotropy have also to be considered to explain the wide range of the splitting pattern observed in the western Mediterranean region. Many geophysical observations such as the low Pn velocity, lower lithospheric Q values, higher heat flow and the presence of high conductive features support the mantle flow in the western Mediterranean, which may contribute and even modify the splitting pattern beneath the studied region.

关键词： shear-wave splitting Seismic anisotropy Iberian Peninsula Northwest Africa Western Mediterranean

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shear-wave splitting beforeand after the 1999 Xiuyan earthquake in Liaoning, China

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Earthquake Science 2008年第4期21卷 344-357+441页

作者：太龄雪高原曹凤娟石玉涛吴晶焦明若 Institute of Earthquake Science China Earthquake Administration Earthquake Administration of Liaoning Province

Using seismic waveform data recorded at station YK (Yingkou) of Liaoning Telemetry Digital Seismic Network, this paper studied the characteristics of shear-wave splitting before and after the Xiuyan MS5.9 (ML5.3) earthquake in November 29, 1999 with SAM method. The results show that the predominant polarizations of fast shear-waves at YK is in direction of ENE-WSW, consistent with the direction of regional principal compressive stress and also consistent with the direction of the regional tectonic stress field in North China; time-delays increasing before Xiuyan earthquake may shows accumulation of stress before earthquake. The predominant polarizations of fast shear-waves at YK are also related to the spatial distribution of small earthquakes and correlate with the fault strike. The histogram of monthly average polarizations of fast shear-waves shows that polarizations of fast shear-waves also seems to change from two months before the earthquake, but it still needs more data for verification.

关键词： Xiuyan earthquake shear-wave splitting polarization time delay

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shear-wave splitting of Sichuan Regional Seismic Network

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Earthquake Science 2008年第2期21卷 127-138+219页

作者：张永久高原石玉涛程万正 Earthquake Administration of Sichuan Province Institute of Earthquake Science China Earthquake Administration

Using seismic data recorded by the Chengdu Digital Seismic Network from May 1, 2000 to December 31, 2006, we obtain the dominant polarization directions of fast shear-waves at eight digital seismic stations adopting the SAM technique. The results show that the dominant directions of polarizations of fast shear-waves at most of sta-tions are mainly in nearly NE-SW or NW-SE direction in Sichuan. The dominant polarization directions of the fast shear-waves at stations located at the active faults or intersection of several active faults are consistent with the strikes of active faults which control the earthquakes used in the analysis, and are basically consistent with the directions of regional compression axis. However, several stations show that the fast shear-waves are not consis-tent with the strikes of active faults and the directions of regional compression axis, due to the influence of local complicated crustal structure.

关键词： shear-wave splitting polarization of fast shear-wave compression axis active fault Sichuan region

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Preliminary analysis of the shear-wave splitting observations from the Qiaojia seismic array

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Earthquake Science 2020年第2期33卷 82-97页

作者： Hao Liang Zhen Fu Chunlai Li Lisheng Xu Institute of Geophysics China Earthquake AdministrationBeijing 100081China

A total of 351 shear-wave splitting results at 25 stations were obtained from the seismic data recorded in period of January,2013 to December,2016,by a broadband seismic array deployed in the northern segment of Xiaojiang Fault Zone(n-XJFZ).Meanwhile,the stress field of the n-XJFZ was determined by inverting 140 focal mechanism solutions of the small earthquakes within the study area which were recorded in the same period.This determination confirmed a compressive stress in NW-SE orientation and an extensional stress in the NE-SW orientation,with little difference from those released by previous studies.The shear-wave splitting results show a spatial complexity in polarization orientation,different from one site to another.How-ever,the polarization orientations integrated for the subareas suggest that the fault trends seemingly played important roles.All the subareas bear two dominant orientations,N10°E and N90°E,both of which are different from the azimuths of the principal compressive stress,due to the fault distribution.The time delay averaged over the entire region is 4.56 ms/km,close to that of the upper boundary of the generally accepted interval worldwide but larger than those in most of the investigated regions in the Chinese mainland,which probably implies an alignment of more micro-cracks in the n-XJFZ.Interestingly,the 2014 Ms6.5 Ludian earthquake was found to have caused a variation in the time delays of the slow shear waves within the study area though its epicenter was outside.This earthquake resulted in an evident drop of the time delays remaining for 4 months,however,lifted a bit the time-delay level with respect to that prior to the earthquake.

关键词： seismic array Xiaojiang fault zone shear-wave splitting polarization orientation time delay

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Variational characteristics of shear-wave splitting on the 2001 Shidian earthquakes in Yunnan, China

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Acta Seismologica Sinica(English Edition) 2004年第6期17卷 635-641页

作者： GAO Yuan(高原) LIANG Wei(梁维) DING Xiang(丁香) XUE Yan(薛艳) CAI Ming-jun(蔡明军) LIU Xi-qiang(刘希强) SU You-jin(苏有锦) PENG Li-guo(彭立国) Institute of Earthquake Science China Earthquake Administration Beijing 100036 China Graduate School Chinese Academy of Sciences Beijing 100039 China Institute of Earthquake Science China Earthquake Administration Beijing 100036 China Institute of Earthquake Science China Earthquake Administration Beijing 100036 China Earthquake Administration of Yunnan Province Kunming 650041 China Earthquake Administration of Shandong Province Ji''nan 250014 China Earthquake Administration of Yunnan Province Kunming 650041 China Center for Comprehensive Surveying China Earthquake Administration Beijing 100039 China

In 2001 three earthquakes occurred in Shidian in Yunnan Province, which were the MS=5.2 on April 10, the MS=5.9 on April 12 and the MS=5.3 on June 8. Based on the data from the station Baoshan of Yunnan Telemetry Digital Seismograph Network, the variational characteristics of shear-wave splitting on these series of strong earthquakes has been studied by using the systematic analysis method (SAM) of shear-wave splitting. The result shows the time delays of shear-wave splitting basically increase with earthquake activity intensifying. However the time delays abruptly decrease immediately before strong aftershocks. It accords with the stress relaxation before earthquakes, which was found recently in study on shear-wave splitting. The result suggests it is significant for reducing the harm degree of earthquakes to develop the stress-forecasting on earthquake in strong active tectonic zones and economic developed regions or big cities under the danger of strong earthquakes.

关键词： shear-wave splitting temporal change earthquake stress-forecasting Shidian earthquakes SAM analysis

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shear-wave splitting in the crust:Regional compressive stress from polarizations of fast shear-waves

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Earthquake Science 2012年第1期25卷 35-45页

作者： Yuan Gao Yutao Shi Jing Wu Lingxue Tai Institute of Earthquake Science China Earthquake AdministrationBeijing 100036China Institute of Geology and Geophysics Chinese Academy of SciencesBeijing 100029China

When propagating through anisotropic rocks in the crust, shear-waves split into faster and slower components with almost orthogonal polarizations. For nearly vertical propagation the polarization of fast shear- wave （PFS） is parallel to both the strike of the cracks and the direction of maximum horizontal stress, therefore it is possible to use PFS to study stress in the crust. This study discusses several examples in which PFS is applied to deduce the compressive stress in North China, Longmenshan fault zone of east edge of Tibetan plateau and Yunnan zone of southeast edge of Tibetan plateau, also discusses temporal variations of PFS orientations of 1999 Xiuyan earthquake sequences of northeastern China. The results are consistent to those of other independent traditional stress measurements. There is a bridge between crustal PFS and the crustal principal compressive stress although there are many unclear disturbance sources. This study suggests the PFS results could be used to deduce regional and in situ principal compressive stress in the crust only if there are enough seismic stations and enough data. At least, PFS is a useful choice in the zone where there are a large number of dense seismic stations.

关键词： polarization of fast shear-wave shear-wave splitting compressive stress in the crust seismic anisotropy

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Anisotropic zoning in the upper crust of the Tianshan Tectonic Belt

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Science China Earth Sciences 2021年第4期64卷 651-666页

作者： Jin LI Yuan GAO Qiong WANG Earthquake Administration of Xinjiang Uygur Autonomous Region Urumqi 830011China Key Laboratory of Earthquake Prediction Institute of Earthquake ForecastingChina Earthquake AdministrationBeijing 100036China

The Tianshan Tectonic Belt is an intracontinental orogenic belt formed by continental convergence that has undergone long-term tectonic evolution. The reactivation that began during the Cenozoic Period has led to complex structural changes. The goals of this study are to review the seismic observational data obtained during 2009–2019 in the Xinjiang regional seismic network and analyze the anisotropy of the upper crust in the Tianshan area. Therefore, a shear-wave splitting system was adopted to collect and analyze shear-wave splitting parameters of 33 stations in the study area. The anisotropy of the upper crust of the Tianshan is spatially diverse, and the dominant polarization directions of fast shear-wave reflect the spatial variations of regional tectonic stress. In addition, the time delays of slow waves are proportional to the intensities of anisotropy in the upper crustal medium. The dominant polarization direction of the fast waves in the western segment of the North Tianshan Mountain,northwestern corner of the Tarim Basin, and northeastern edge of Pamir is consistent with the tectonic stress fields in the area. In the northern part of the Keping Block, the dominant polarization directions of the fast waves are consistent with the fault trends;however, they are at a high angle to the dominant directions of the regional tectonic stress field indicating that the anisotropy is affected by the faults in the area. The anisotropy of the eastern segment of the South Tianshan Mountains and the surrounding area of Urumqi are affected by the local stress field and fault structure. The polarization directions at some of the stations are subparallel to the directions of the regional principal stress. However, for other stations, the polarization directions are aligned with the neighboring faults. The polarization directions of the fast waves in most of the study area are consistent with the local tectonic stress fields. Thus, stress compression phenomena such as the Tarim Basin being thrusted and subducted between t

关键词： Tianshan Tectonic Belt Seismic anisotropy shear-wave splitting Tectonic stress

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The Physics Underlying Gutenberg-Richter in the Earth and in the Moon

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Journal of Earth Science 2015年第1期26卷 134-139页

作者： Stuart Crampin Yuan Gao British Geological Survey Edinburgh EH9 3LAScotland UK School of Geosciences University of Edinburgh EH9 3FWScotland UK Institute of Earthquake Science China Earthquake Administration

The linear Gutenberg-Richter relationship is well-established. In any region of the Earth, the logarithm of the number of earthquakes, greater than any magnitude, is proportional to magnitude. This means that the underlying physics is non-linear and not purely elastic. This nonlinear physics has not been resolved. Here we suggest that a new understanding of fluid-rock deformation provides the physics underlying Gutenberg-Richter： where the fluid-saturated microcracks in almost all in situ rocks are so closely-spaced that they verge on failure and fracture, and hence are critical-systems which impose fundamentally-new properties on conventional sub-critical geophysics. The observation of linear Gutenberg-Richter relationship in moonquakes suggests that residual fluids exist at depth in the Moon.

关键词： critical-system Gutenberg-Richter relationship New Geophysics residual fluid inmoonquake shear-wave splitting shear-wave time-delay.

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Crustal seismic anisotropy in southeastern Capital area, China

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Earthquake Science 2008年第1期21卷 1-10+108页

作者：吴晶高原陈运泰 Beijing 100081 China Institute of Earthquake Science China Earthquake Administration Beijing 100036 China Institute of Geophysics China Earthquake Administration Institute of Geophysics China Earthquake Administration

shear-wave splitting parameters of 24 stations in southeastern Capital area of North China （38.5°N;9.85°N, 115.5°E;18.5°E） are obtained with systematic analysis method of shear-wave splitting （SAM） based on the data recorded by Capital Area Seismograph Network （CASN） from 2002 to 2005. The results show that the average polarization of fast shear-wave in southeastern Capital area is consistent with regional maximum horizontal prin- cipal compressive stress in the area, and is also consistent with maximum horizontal principal compressive strain from GPS in North China. The average shear-wave splitting in southeastern Capital area （in basin） is different from that in northwestern Capital area where uplifts and basin exist, which means that tectonics can be related to shear-wave splitting results. Research also shows that the distribution of faults around stations can obviously affect the shear-wave splitting results, and complicated distribution of faults can result in much more scatter of shear-wave splitting. Moreover, in the north and south of the studied area （southeastern Capital area）, the polariza- tions of fast shear-wave are not very consistent, which may be related to differences in tectonic and stress for the two areas.

关键词： southeastern Capital area seismic anisotropy shear-wave splitting crust stress

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