2015年尼泊尔M_S8.1地震在喀什—乌恰交汇区的动态触发活动

Remotely Triggered Seismicity around Kashi—Wuqia Area Following the 2015 M_S8.1 Nepal Earthquake

基于新疆区域数字地震台网台站的观测资料,采用离散波数法、包络函数分析和β统计值检验的方法,初步研究尼泊尔M_S8.1地震对喀什—乌恰交汇区小震活动的动态触发作用。结果表明:尼泊尔8.1级地震在喀什—乌恰交汇区接收点产生的动态应力变化超过触发阈值;并检测到该地震面波到达后在此交汇区出现了8次小震事件。β统计值结果显示,8.1级地震后此交汇区的地震活动性发生了较明显的改变,特别是地震25天后地震活动率增强较为明显。综合分析认为,尼泊尔8.1级地震对喀什—乌恰交汇区的小震活动具有动态触发作用,触发时间既存在面波通过后即刻触发,也有滞后一段时间的延时触发。

In this paper, we report our preliminary research on the dynamic triggering function of the Nepal Ms8.1 earthquake with respect to microearthquake activity in the Kashi-Wuqia intersection area. We also discuss the triggering influence of the earthquake on activities at the Kashi Wuqia intersection area based on observation data from the Xinjiang regional digital seis- mic network station. In this study, we used the discrete wave number method and performed envelope function waveform analysis, spectrum analysis, and β statistical test methods. The results show that after the Nepal 8.1 earthquake, the dynamic stress change produced at the Kashi-Wu- qia intersection area exceeded the dynamic stress triggering threshold. Using the envelope func- tion method, we determined that after the Nepal 8.1 earthquake, at least eight microearthquakesoccurred at theKashi Wuqia intersection area before the arrival of a seismic surface wave. Six of these microearthquakes had not yet been identified by the regional seismic network or any single station location. Our β statistical results show that after the Nepal 8.1 earthquake, the seismic ac- tivities at the Kashi-Wuqia intersection area obviously changed, especially on the day of the earthquake, with the daily frequency of seismic activities being about ten times that in the month prior to the earthquake. Twenty-five days after the Nepal 8.1 earthquake, the seismic activities at the Kashi Wuqia intersection area strengthened significantly. After comprehensive analysis, we consider that the Nepal 8.1 earthquake had a certain dynamic triggering function with respect to the microearthquake activity that occurred in the Kashi--Wuqia intersection area. The triggering time included not only the immediate dynamic stress trigger after the passage of the surface wave, but also the delayed dynamic stress trigger, which may have remained in a subcritical state with the stress of the Kashi Wuqiaintersection area. Fault rupture may require further accumu lation or dynamic stress changes to affect the fault instability rate. Instability may be present long before dynamic stress ends despite the absence of any weakening.