Relocation of aftershocks of the Wenchuan M S 8.0 earthquake and its implication to seismotectonics

Abstract

From 14:28 (GMT+8) on May 12th, 2008, the origin time of MS8.0 Wenchuan earthquake, to December 31th, 2008, more than 10 000 aftershocks (M ≥2.0) had been recorded by the seismic networks in Sichuan and surrounding areas. Using double difference algorithm, the main shock and more than 7 000 aftershocks were relocated. The aftershocks distribute about 350 km long. The depths of aftershocks are mainly between 10 km and 20 km. The average depth of aftershocks is about 13 km after relocation. In the southwest, the distribution of aftershocks is along the back-range fault, the central-range fault and the front-range fault of Longmenshan faults. In the middle, the distribution of aftershocks is along the central-range fault. In the north, aftershocks are relocated along the Qingchuan-Pingwu fault. Relocations suggest that the back-range fault mainly induced and controlled the aftershock occurrence in the northern section of aftershocks sequence. The MS8.0 main shock is between central-range and front-range of Longmenshan faults and is near the shear plane of the fault bottom. From the depth distribution of aftershock sequence, it suggests that these three faults show imbricate thrust structure.

Implication of Radon Monitoring for Earthquake Surveillance Using Statistical Techniques: A Case Study of Wenchuan Earthquake

“…Initially, this anomalous trend is observed 5 days prior to the Wenchuan earthquake on May 07, 2008, and continued until July 2008 showing post earthquake anomalies. It is important to mention that these post earthquake changes were possibly associated with the aftershock sequence of the Wenchuan earthquake [50]. Similarly, the SPS monitoring station having R E /R D ≈ 0:073 and R E ≈ 182 km shows a multifold increase in the daily Rn levels around the time of the Wenchuan earthquake (Figure 3(d)).…”

Using surface wave amplitude spectra to estimate the source depth of Sichuan Jiuzhaigou <italic>M</italic>7.0 earthquake

“…本研究利用AK135模 系发生大规模的向东、东南方向的"逃逸"运动 [16] . [9,10,17] , 区域内地震活动背景一直很 强 [18] , 2008年M8.0汶川地震和2013年M7.0芦山地震发 生在该区域东部的龙门山断裂带上 [10,19,20] . 图 3 原始波形与相位匹配滤波后的波形.…”

龙门山断裂带中南段的一个破裂空段——芦山地震的震后效应

“…根据汶川地震余震序列的重新定位结果 [19] , 这 次的芦山地震余震序列发生在汶川地震的西南方向, 位于龙门山断裂带的南段. 从空间上看, 在龙门山断 裂带的中南段, 芦山地震及余震分布与汶川地震及 余震分布(即是在汶川和芦山之间), 形成一个地震活 动空段, 或称"破裂空段"(图 6).…”

“…通过对龙门山断裂带上汶川地震和芦山地震 的余震活动及剪切波分裂研究, 给出了关于震源位 置 [19,27] 及应力环境的信息 [8,10,14,28] , 本文的分析显示, 在芦山地震震中沿着龙门山断裂带向西南方向, 到 与鲜水河断裂带、安宁河断裂交汇区附近, 区域主压 应力从近 NW 方向, 变为近 EW 方向. 这种应力方向 的空间变化, 揭示了深部构造运动的信息, 进一步的 研究需要加强.…”