RELOCATION OF THE AFTERSHOCK SEQUENCE OF THE MS6.5 LUDIAN EARTHQUAKE AND ITS SEISMOGENIC STRUCTURE

doi:10.3969/j.issn.0253-4967.2014.04.019

Abstract

Abstract:

We integrated two-month phase data recorded by Yunnan Seismic Network, Zhaotong Seismic Network, Qiaojia Seismic Array and temporal stations deployed around the Ludian earthquake source region and relocated the aftershock sequence of the Ludian earthquake. The locations of 1 750 aftershocks were determined using double-difference location algorithm. The relocation result shows that the aftershock distribution has two predominant directions, to the southeast and southwest, and shows itself as an asymmetric conjugate shape. The lengths of the two aftershock strips are about 16km. The angle between the two strips is about 100°. Aftershock distribution shows that the seismogenic fault of the Ludian earthquake is a high-angle strike-slip fault. The mainshock is located at the middle at southwest of the two aftershock strips. Early aftershocks are distributed mainly along the NW-SE direction, perpendicular to the Zhaotong-Ludian Fault. The aftershocks located to the southwest of the mainshock may be triggered by the mainshock. According to the aftershock distribution and its relations with neighboring faults, focal mechanism of the mainshock, the long axis orientation of seismic intensity map, and distribution of landslides, we speculate that the seismogenic fault is the Baogunao-Xiaohe Fault. There are significant differences not only in seismic activity, deep velocity structure, but also the block movement direction and rate on both sides of the Baogunao-Xiaohe Fault. The northward expansion of aftershock activity may be blocked by the high-velocity anomaly zone located on the north side of the Baogunao-Xiaohe Fault.

Key words: Ludian earthquake, aftershock sequence, earthquake relocation, seismogenic fault

摘要：

整合了鲁甸震区周边的云南省地震台网、昭通市地震台网、巧家台阵, 以及流动台站2个月的震相观测数据, 对鲁甸地震序列进行了重新定位, 得到了1 750个地震的震源参数.重定位结果显示, 余震有2个优势分布方向, 分别为SE向和SW向, 具有不对称的共轭分布特征.2个余震条带的展布长度相当, 约为16km, 夹角约100°.余震分布显示鲁甸地震的发震断层为高倾角的走滑断层.主震位于2个余震条带中间略偏西南的位置, 早期余震主要沿NW-SE向垂直于昭通-鲁甸断裂分布, 主震西南侧的余震可能为后期触发的.根据余震分布与周边断层的关系、主震震源机制、烈度分布的长轴方位, 以及滑坡分布等资料, 认为鲁甸地震的发震断层为NW向的包谷垴-小河断裂.包谷垴-小河断裂南北两侧无论是在地震活动、深部速度结构, 还是块体运动方向和速率方面都存在显著差异, 断裂北侧的高速异常可能是阻止余震向北继续扩展的主要原因.

关键词: 鲁甸地震, 余震序列, 地震定位, 发震断层

CLC Number:

P315.63

FANG Li-hua, WU Jian-ping, WANG Wei-lai, LÜ|Zuo-yong, WANG Chang-zai, YANG Ting, ZHONG Shi-jun. RELOCATION OF THE AFTERSHOCK SEQUENCE OF THE M_S6.5 LUDIAN EARTHQUAKE AND ITS SEISMOGENIC STRUCTURE[J]. SEISMOLOGY AND GEOLOGY, 2014, 36(4): 1173-1185.

房立华, 吴建平, 王未来, 吕作勇, 王长在, 杨婷, 钟世军. 云南鲁甸M_S6.5地震余震重定位及其发震构造[J]. 地震地质, 2014, 36(4): 1173-1185.

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