FOCAL MECHANISM AND SEISMOGENIC STRUCTURE OF THE M5.0 YUEXI EARTHQUAKE ON 1 OCT. 2014, SOUTHWESTERN CHINA

doi:10.3969/j.issn.0253-4967.2016.04.025

Abstract

Abstract:

The Oct.1,2014 M5.0 Yuexi earthquake occurred on the Daliang Shan fault zone where only several historical moderate earthquakes were recorded.Based on the waveform data from Sichuan regional seismic network,we calculated the focal mechanism solution and centroid depth of the M5.0 Yuexi earthquake by CAP (Cut and Paste) waveform inversion method,and preliminarily analyzed the seismogenic structure.We also calculated the apparent stress values of the M5.0 earthquake and other 14 M_L≥4.0 events along the Shimian-Qiaojia fault segment of the eastern boundary of the Sichuan-Yunnan block.The result indicates that the parameters of the focal mechanism solution are with a strike of 256°,dip of 62°,and slip of 167° for the nodal plane Ⅰ,and strike of 352°,dip of 79°,and slip of 29° for the nodal plane Ⅱ.The azimuth of the P axis is 121° with dip angle of 11°,the azimuth of T axis is 217° with dip angle of 28°,and the centroid depth is about 11km,and moment magnitude is M_W5.1.According to the focal mechanism solution and the fault geometry near the epicenter,we infer that the seismogenic fault is a branch fault,i.e.,the Puxiong Fault,along the central segment of the Daliang Shan fault zone.Thus,the nodal plane Ⅱ was interpreted as the coseismic rupture plane.The M5.0 Yuexi earthquake is a strike-slip faulting event with an oblique component.The above findings reveal the M5.0 Yuexi earthquake resulted from the left-lateral strike-slip faulting of the NNW Dalang Shan fault zone under the nearly horizontal principal compressive stress regime in an NWW-SEE direction.The apparent stress value of the Yuexi earthquake is 0.99MPa,higher than those of the M_L ≥ 4.0 earthquakes along the eastern boundary of the Sichuan-Yunnan block since 2008 Wenchuan M8.0 earthquake,implying a relatively high stress level on the seismogenic area and greater potential for the moderate and strong earthquake occurrence.It may also reflect the current increasing stress level of the entire area along the eastern boundary,and therefore,posing the risk of strong earthquakes there.

Key words: M5.0 Yuexi earthquake, focal mechanism, seismogenic structure, Daliang Shan fault zone, apparent stress

摘要：

2014年10月1日越西M5.0（或M_L5.2）地震发生在川滇块体东边界历史地震强度较低的大凉山断裂带中段。基于四川区域地震台网记录的波形资料，利用CAP（Cut and Paste）波形反演方法，计算了越西M5.0地震的震源机制解与震源矩心深度，初步分析了本次地震的发震构造。同时，利用波形资料，计算了该地震的视应力值，并与2001年以来附近区域M_L≥4.0地震的视应力值进行了对比分析。研究结果表明，越西M5.0地震震源机制解节面I走向256°/倾角62°/滑动角167°，节面Ⅱ走向352°/倾角79°/滑动角29°；P轴方位121°，仰角11°，近水平；T轴方位217°，仰角28°；震源矩心深度为11km；矩震级约为M_W5.1。根据节面参数与震中附近的主要构造展布，认为此次地震的发震构造为大凉山断裂带中段分支断裂——NNW向普雄断裂，与该断裂走向相近的节面Ⅱ为同震破裂面。本次地震为兼具小量逆冲分量的左旋走滑型地震，是NNW向大凉山断裂带在近水平的NWW-SEE向主压应力作用下左旋走滑活动所致。此外，利用波形资料计算获得的越西M5.0地震的视应力值（0.99MPa）高于汶川8.0级地震后其附近区域的地震视应力，反映了震源区当前的背景应力水平相对较高，有利于中、强地震的发生，越西地震的视应力高值还可能反映了川滇块体整个东边界区域当前的应力水平在逐渐升高，因而发生强震的危险性也在升高。

关键词: 越西M5.0地震, 震源机制, 发震构造, 大凉山断裂带, 视应力

CLC Number:

P315.2

YI Gui-xi, LONG Feng, ZHAO Min, GONG Yue, ZHANG Zhi-wei, QIAO Hui-zhen. FOCAL MECHANISM AND SEISMOGENIC STRUCTURE OF THE M5.0 YUEXI EARTHQUAKE ON 1 OCT. 2014, SOUTHWESTERN CHINA[J]. SEISMOLOGY AND GEOLOGY, 2016, 38(4): 1124-1136.

易桂喜, 龙锋, 赵敏, 宫悦, 张致伟, 乔慧珍. 2014年10月1日越西M5.0地震震源机制与发震构造分析[J]. 地震地质, 2016, 38(4): 1124-1136.

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