Focal Mechanism of the Xianyou Earthquake Sequence, Fujian, China
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1,209 earthquakes occurred in Xianyou,Fujian from August 4,2010 to October 4,2013.The largest earthquake was M L5. 0 on September 4,2013. In order to study the Xianyou earthquake sequence and understand the causative structure and stress field of Xianyou,the focal mechanism solutions of six earthquakes( M L> 3. 5) in the Xianyou earthquake sequence are calculated using the broadband digital data of the Fujian Seismic Network with the seismic moment tensor inverse method. The results show that the focal faults of the six earthquakes are similar,which are all strike-slip faults striking to the northwest with high dip angles. The direction of the principal compressive stress axes is near SN,which is different from the stress field of Fujian region. The Xianyou earthquake sequence may have been induced by the stress adjustment after the impoundment of Jinzhong reservoir.Keywords:
Focal mechanism
Sequence (biology)
Stress field
Seismic moment
Moment tensor
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There was an earthquake swarm of two major events of MS6.3 and MS5.8 on the Xianshuihe fault in November, 2014. The two major earthquakes are both strike-slip events with aftershock zone along NW direction.We have analyzed the characteristics of this earthquake sequence. The b value and the h value show the significant variations in different periods before and after the MS5.8earthquake. Based on the data of historical earthquakes, we also illustrated the moderate-strong seismic activity on the Xianshuihe fault. The Kangding earthquake swarm manifests the seismic activity on Xianshuihe fault may be in the late seismic active period. The occurrence of the Kangding earthquake may be an adjustment of the strong earthquakes on the Xianshuihe fault. The Coulomb failure stress changes caused by the historical earthquakes were also given in this article. The results indicate that the earthquake swarm was encouraged by the historical earthquakes since1893, especially by the MS7.5 Kangding earthquake in1955. The Coulomb failure stress changes also shows the subsequent MS5.8 earthquake was triggered by the MS6.3earthquake.
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The Minxian- Zhangxian A/6.6 earthquake,with a focal depth of 20 km,occurred at the boundary of Minxian and Zhangxian counties(34.5°N,104.2°E),Dingxi city,Gansu Province,at 7:45CST on July 22,2013.By 8:00 on July 29,1034 aftershocks occurred.Among them,nine above A/3.0 include one M5.0-5.9,one M4.0-4.9,and seven M3.0-3.9 earthquakes.The strongest aftershock,which occurred at 9:12 on the date of the mainshock,attained A/s5.6.Catastrophic damages caused by this earthquake are mainly attributed to poor residential structures erected by the government during a weak economy.The affected area was more than 10 000 km~2 and involved in 6 cities and 13 counties including Dingxi,Baiyin,Tianshui,Longnan,and Gannan Zang and Linxia Hui autonomous prefectures.Residents in Baoji,Hanzhong,Xianyang,Xi'an,Chengdu,and Mianyang felt this earthquake.The earthquake occurred at southeastern region of Gansu province,which is covered by very thick loess layer and exhibits complex topography such as steep,highly sloped mountains and crisscrossed ravines.It killed 95 people and injured 1 366.Secondary disasters caused by this earthquake include loess landslides,collapses,and pitfalls.Immediately following the earthquake,the China Earthquake Administration quickly organized field survey teams for seismicity monitoring,intensity studies,earthquake damage assessment,and scientific research,through which the first intensity distribution map of the Minxian- Zhangxian M6.6 earthquake was developed for conditions at 14:00 on July 24.The macroscopic epicenter of this earthquake,with an intensity of VIII degrees,was located at Yongguang and Yongxing villages of Meichuan and Lalu Village of Hetuo.The long axes of intensity circled with an NW strike,in accordance with regional structures.This study discusses the basic parameters of this earthquake such as basic intensity distribution,damage features and seismogenic structure.This earthquake occurred at the eastern margin of the Qinghai- Tibetan Plateau at the intersection of the N- S seismic zone and the Kunlun- Qinling fault zone,which is the tectonic transformation zone between the NWW east-striking Kunlun fault and the northern margin of the western Qinling fault zone.We determined that the Hetuo fault,active since the late Pleistocene,passes through the extreme seismic area.Surface rupture phenomena such as landslides,ground fissures,earthquake pitfalls,sandblasting,and water oozing all exhibited zonal distribution along the Hetuo fault.The focal mechanism of this earthquake is consistent with the Hetuo fault.The strike of the nodal plane II is 320° and 301.3°,as reported respectively by the Institute of Geophysics and the Institute of Geology,China Earthquake Administration,which also corresponds to the strike of the Hetuo fault.Moreover,the NE-dipping slip plane reported by the two agencies,51 ° and 57.3°,respectively,corresponds with the dipping direction of the Hetuo fault.Further,we determined that the Anjia Shan landslide slips laterally along a fault valley striking NW that resembles a long tongue with length and width of 310 m and 30-35 m,respectively.The plunge angel of fault striations on the slip plane is 12°-23°,and the main slip plane corresponds with the fault strike.Therefore,the Hetuo fault is seismogenic fault of the Minxian- Zhangxian A/6.6earthquake,which is a secondary fault,belongs to the Lintan- Tanchang fault zone.Three strong earthquakes above A/6.0 have occurred near the epicenter of the Minxian- Zhangxian A/6.6 earthquake on the Lintan fault,and two moderate earthquakes have occurred at this site in recent years,which include the Minxian M5.2 on November 13,2003,and the Minxian- Zhuoni M5.0 on September 7,2004.This earthquake represents the most recent activities of the Lintan- Tanchang fault zone.
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Research Article| January 01, 2014 Possibility of the Independence between the 2013 Lushan Earthquake and the 2008 Wenchuan Earthquake on Longmen Shan Fault, Sichuan, China Ke Jia; Ke Jia aSchool of Earth and Space Sciences, Peking University, Beijing 100871, Chinajk@pku.edu.cn Search for other works by this author on: GSW Google Scholar Shiyong Zhou; Shiyong Zhou aSchool of Earth and Space Sciences, Peking University, Beijing 100871, Chinajk@pku.edu.cn Search for other works by this author on: GSW Google Scholar Jiancang Zhuang; Jiancang Zhuang bThe Institute of Statistical Mathematics, 10‐3 Midori‐Cho, Tachikawa, Tokyo 190‐8562, Japan Search for other works by this author on: GSW Google Scholar Changsheng Jiang Changsheng Jiang cInstitute of Geophysics, China Earthquake Administration, No. 5 Minzu Daxue Nan Road, Haidian District, Beijing 100086, China Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2014) 85 (1): 60–67. https://doi.org/10.1785/0220130115 Article history first online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Ke Jia, Shiyong Zhou, Jiancang Zhuang, Changsheng Jiang; Possibility of the Independence between the 2013 Lushan Earthquake and the 2008 Wenchuan Earthquake on Longmen Shan Fault, Sichuan, China. Seismological Research Letters 2014;; 85 (1): 60–67. doi: https://doi.org/10.1785/0220130115 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search The 20 April 2013 Lushan earthquake, Ms 7.0 (China Earthquake Data Center [CENC]) or Mw 6.6 (U.S. Geological Survey [USGS]), with 196 people killed, and more than 10,000 injured according to the local government's official report, was the strongest earthquake after the 12 May 2008, Ms 8.0 (CENC) or Mw 7.9 (USGS), Wenchuan earthquake in Sichuan province, China. This earthquake occurred in the southwestern part of the Longmen Shan fault zone, which also was the same causative fault zone of the 2008 Wenchuan earthquake (Fig. 1). The epicenter and focal depth of the Lushan earthquake... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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The great Sanhe-Pinggu M8 earthquake occurred in 1679 was the largest surface rupture event recorded in history in the northern part of North China plain. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method.Based on the assumption that clustered small earthquakes often occur in the vicinity of fault plane of large earthquake, and referring to the morphology of the long axis of the isoseismal line obtained by the predecessors, we selected a strip-shaped zone from the relocated earthquake catalog in the period from 1980 to 2009 to invert fault plane parameters of this earthquake. The inversion results are as follows: the strike is 38.23°, the dip angle is 82.54°,the slip angle is-156.08°, the fault length is about 80 km,the lower-boundary depth is about 23 km and the buried depth of upper boundary is about 3 km. This shows that the seismogenic fault is a NNE-trending normal dip-slip fault,southeast wall downward and northwest wall uplift, with the right-lateral strike-slip component. Moreover, the surface rupture zone, intensity distribution of the earthquake and seismic-wave velocity profile in the focal area all verified our study result.
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The Seismogenic Structure and Deformation Mechanism of the Lushan（MW 6.6） Earthquake, Sichuan, China
On April 20 th, 2013, an earthquake of magnitude MW 6.6 occurred at Lushan of Sichuan on the southern segment of the Longmenshan fault zone, with no typical coseismic surface rupture. This work plotted an isoseismal map of the earthquake after repositioning over 400 post–earthquake macro–damage survey points from peak ground acceleration(PGA) data recorded by the Sichuan Digital Strong Earthquake Network. This map indicates that the Lushan earthquake has a damage intensity of IX on the Liedu scale, and that the meizoseismal area displays an oblate ellipsoid shape, with its longitudinal axis in the NE direction. No obvious directivity was detected. Furthermore, the repositioning results of 3323 early aftershocks, seismic reflection profiles and focal mechanism solutions suggests that the major seismogenic structure of the earthquake was the Dayi Fault, which partly defines the eastern Mengshan Mountain. This earthquake resulted from the thrusting of the Dayi Fault, and caused shortening of the southern segment of the Longmenshan in the NW–SE direction. Coseismal rupture was also produced in the deep of the Xinkaidian Fault. Based on the above seismogenic model and the presentation of coseismic surface deformation, it is speculated that there is a risk of more major earthquakes occurring in this region.更多还原
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Using the joint inversion method with the amplitude ratio of P-wave,SV-wave and SHwaves,this paper calculates the focal mechanisms of the aftershock sequence of the Yaoan earthquake with MS6. 0. According to the spatial distribution of earthquake sequence,the author analyzes the characteristics of the stress field and seismogenic fault. The result shows that:( 1) the seismogenic fault of the Yaoan earthquake is a vertical right-lateral strike-slip fault,striking NWW-SEE. The result is reliable and consistent with the nodal planes of the Harvard CMT solution and also in accord with the predominant direction of aftershocks.( 2) The predominant direction of principal compressive stress,NWW-SEE is consistent with the regional tectonic stress,and some aftershocks are different from the main shock. The stress field of the main shock is controlled by the regional tectonic stress field,indicating the diversity and complexity in the seismic area.( 3) By comprehensively analyzing the distribution of the earthquake sequence,focal mechanism and fault structure in the seismic area,it is found that the Maweijing fault is the seismogenic fault of the Yaoan earthquake.
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The focal mechanism solutions of the M5. 1 Badong earthquake and subsequent 34 aftershocks at ML 2. 0 or more were calculated using the P-wave first motion method; the main earthquake was normal fault dip slip type, and the slip types of the seismogenic rupture surfaces of the subsequent aftershocks primarily include normal dip slip (14 times), reverse dip slip (9 times), normal strike slip (9 times) and reverse strike slip (2 times). The M5. 1 Badong earthquake activities may be related to the stress adjustment caused by the rise of the groundwater level and the decrease of the frictional resistance betvveen structural planes of rock formations due to the effect of reservoir water penetration, and related to the joint activities of the NE-strike Gaoqiao fault and the near EW-strike Daping fault.
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An M_S7.3 earthquake occurred on February 12,2014 in Yutian County,Xinjiang Uygur Autonomous Region,which was followed by a series of aftershocks. This paper calculates the depth of the M_S7.3 earthquake sequence by using the deterministic approach with the seismic phase data from the catalog database of the China Earthquake Networks Center,combined with original seismic wave records from the Digital Seismic Network Center of the Earthquake Administration of Xinjiang Uygur Autonomous Region.
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The mainshock location of the Badong Ms5.1 earthquake is determined using four location methods: the simplex method, HYP2000, hyposat, and locSAT; the 350 aftershocks over 3 months are relocated using the double difference location method. The results indicate that aftershocks are distributed as bands along the NEE direction and that the aftershocks 1 month after the mainshock, which are mainly distributed in the west of the mainshock and near the Gaoqiao fault, are shallow earthquakes within 5 km; the depth of each aftershock after one month is deeper, and two distinct fault planes, for which the geological occurrence is similar to the Gaoqiao and Zhoujiashan-Niukou fault, are shaped. The frequency-spectrum analysis of the recorded waveform in 12 seismic events indicates that the corner frequency of the mainshock is significantly lower than that of its aftershock and is also lower than a tectonic earthquake of the same magnitude. We considered that this result is related to the constraint of the parameter calibration relationship in the focal spectrum and the lithology change due to water erosion. Combined with the focal mechanism and geological tectonic setting, we conclude that the occurrence of the earthquake is related to the activity of the Daping and Gaoqiao fault and is a reservoir-induced tectonic seismicity.
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