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Some evidences for earthquake occurrence in the shallow crust in some areas of North China and Southwest China

Acta Seismologica Sinica(English Edition) 2001年第4期14卷 456-465页

作者：胡新亮刁桂苓高景春张四昌张学民李钦祖秦清娟朱振兴张彦清 1. Seismological Bureau of Hebei Province 050021 Shijiazhuang China

The parameters of hypocentral location are important fundamental data for the study of seismology and the earth interior physics; among them, the focal depth is a very important one but can hardly be measured with higher precision. With the increase of seismic stations in number, the heightening of observation quality and the improvement of determination method, such a situation has been changed much. In this paper, the results of hypocentral location and re-location by 7 small-aperture digital seismic station networks at Tangshan, Zhangbei and Huailai of Hebei Province, Datong of Shanxi Province and Jianchuan, Luquan and Yao'an of Yunnan Province are used. Using these results together with those of focal depth inversion by far-field data of some individual large shocks in corresponding areas and those re-determined by the Linfen telemetered seismic network of Shanxi Province, a comparison with the results of focal depth determination in the past earthquake catalogues is made. It is found out that the focal depths determined by the small-aperture seismic networks are basically distributed in the range from the earth surface to ten-odd kilometers underground. In contrast, the focal depths determined in the past are mostly distributed at the depth range from the earth surface to 30 km underground. Besides, there is a difference of 50% to 100% between the average values of the two cases, which is quite an obvious one. From the result of analysis, it is considered that the results determined by the small-aperture seismic networks may be closer to the reality of focal depths distribution. That is to say, earthquakes in the above-mentioned areas should be distributed in the shallow part of the crust. The causes that lead to the above situation are discussed preliminarily, and some suggestions and measures for improving the precision of focal depth determination are put forward.

关键词： North China region Southwest China region focal depth shallow crust

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shallow Structure of the crust in the Sulu-Dabie Region,China and its Seismotectonic Implication

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Acta Geologica Sinica(English Edition) 2021年第3期95卷 988-995页

作者： XU Jiren LI Haibing QI Xuexiang ZHAO Zhixin Jiangsu Donghai-Sichuan Longmenshan crustal Activity National Observation and Research Station DonghaiJiangsu 222300China Key Laboratory of Deep-Earth Dynamics Ministry of Natural ResourcesBeijing 100037China Institute of Geology Chinese Academy of Geological SciencesBeijing 100037China

The P-wave velocity structure in the shallow crust is investigated in and around the Sulu-Dabie region by using seismic reflection data for deep soundings in 48 survey profiles and from rock velocity *** observed velocity distributions show obvious heterogeneities in this *** low velocity anomalies are observed mainly in the west of the Dabie region and the East Sea *** high velocity anomalies emerge in the shallow crust of the Sulu and Dabie *** high-velocity anomalies can be attributed to the ultra-high pressure metamorphosed(UHPM)rock formed by exhumation motion of mantle materials during the *** high-velocity anomalies in the different shallow layers beneath the Sulu region are located to the northeast of the Tan-Lu *** high-velocity anomalies beneath the Dabie region are located southwest of the Tan-Lu *** a distribution pattern of velocity anomaly zones may reveal historical motion of a left-lateral strike-slip for the Tan-Lu fault,which differs from the result of a right-lateral strike-slip motion regime known from modern seismology,indicating a more complex tectonic motion along the Tan-Lu fault.

关键词： high seismic velocity anomaly shallow crust strike-slip motion Tan-Lu fault Sulu-Dabie orogen

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shallow crustal velocity structures revealed by active source tomography and fault activities of the Mianning–Xichang segment of the Anninghe fault zone, Southwest China

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Earth and Planetary Physics 2022年第2期6卷 204-212页

作者： XiHui Shao HuaJian Yao Ying Liu HongFeng Yang BaoFeng Tian LiHua Fang Laboratory of Seismology and Physics of Earth’s Interior School of Earth and Space SciencesUniversity of Science and Technology of ChinaHefei 230026China Mengcheng National Geophysical Observatory University of Science and Technology of ChinaMengcheng Hefei 233500China CAS Center for Excellence in Comparative Planetology University of Science and Technology of ChinaHefei 230026China Earth System Science Programme Faculty of ScienceThe Chinese University of Hong KongHong Kong 999077China Shenzhen Research Institute The Chinese University of Hong KongShenzhen 518057China Institute of Geophysics China Earthquake AdministrationBeijing 100089China

The Anninghe fault is a large left-lateral strike-slip fault in southwestern China. It has controlled deposition and magmatic activities since the Proterozoic, and seismic activity occurs frequently. The Mianning-Xichang segment of the Anninghe fault is a seismic gap that has been locked by high stress. Many studies suggest that this segment has great potential for large earthquakes(magnitude >7). We obtained three vertical velocity profiles of the Anninghe fault(between Mianning and Xichang) based on the inversion of P-wave first arrival times. The travel time data were picked from seismograms generated by methane gaseous sources and recorded by three linearly distributed across-fault dense arrays. The inversion results show that the P-wave velocity structures at depths of 0-2 km corresponds well with the local lithology. The Quaternary sediments have low seismic velocities, whereas the igneous rocks,metamorphic rocks, and bedrock have high seismic velocities. We then further discuss the fault activities of the two fault branches of the Anninghe fault in the study region based on small earthquakes(magnitudes between ML 0.5 and ML 2.5) detected by the Xichang *** eastern fault branch is more active than the western branch and that the fault activities in the eastern branch are different in the northern and southern segments at the border of 28°21′N. The high-resolution models obtained are essential for future earthquake rupture simulations and hazard assessments of the Anninghe fault zone. Future studies of velocity models at greater depths may further explain the complex fault activities in the study region.

关键词： Anninghe fault zone shallow crust P-wave velocity methane gaseous source fault activity

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Multi-Layer Strain Rate Field Controlled by Netlike Plastic-Flow in the Lithosphere in Central-Eastern Asia

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Earthquake Research in China 2006年第3期20卷 326-338页

作者： Wang Sheng-zu State Key Laboratory of Earthquake Dynamics Institute of Geology CEA Beijing 100029 China

According to the ＂Netlike Plastic-Flow （NPF）＂ continental dynamics model, the transition of the deformation regime from brittle in shallow layers to ductile in deep layers in the lithosphere, and the controlling effect of NPF in the lower lithosphere result in intraplate multilayer tectonic deformation. NPF is a viscous （plastic） flow accompanied by shear strain localization, forming a plastic-flow network in the lower lithosphere. The strain rates in the seismogeulc layer can be estimated using the ＂earthquake-recurrence-interval＂ method, in which the strain rate is calculated in terms of the recurrence interval of two sequential earthquakes and the seismic probability of the second earthquake. The strains in the lower lithosphere are estimated using the ＂conjugate-angle＂ method, which takes the relationship between the conjugate angles and the compressive strains of the network, and calculates the characteristic strain rates in this layer from the strains and the durations of deformation inferred. The contour map of characteristic maximum principal compressive strain rates in the lower lithosphere in central-eastern Asia given in the paper shows strain rates with magnitudes on the order of 10^-15 - 10^-14/s in this region. The strain rates within the plastic-flow belts, which control seismic activities in the seismogeulc layer, are greater than the characteristic strain rates of the network and, in addition, the strain rates and seismic activities in the seismogeulc layer are also influenced by other factors, including the directive action of driving boundary along the upper crust, the effects of plastic-flow waves and the existence of the transitional weak layer distributed discontinuously between the upper and lower layers. The comparison between the strain rates in the seismogeulc layer and the characteristic strain rates in the lower lithosphere for 11 potential hypocenter areas in the region from the Qinghai-Xizang （Tibet） plateau to the North China plain ind

关键词： Central-eastern Asia Lower lithosphere Seismogenic layer shallow crust Strainrate

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