2015年河北滦县震群发震机理分析

Seismological mechanism analysis of 2015 Luanxian swarm,Hebei province

震群发震机理研究是近年来地震学研究的热点之一,其中基于观测现象对不同发震机理模型的分析和讨论是研究焦点.本文以2015年河北滦县震群为研究对象,首先通过模板匹配方法检测震群活动期间目录遗漏地震事件,得到更为完整的地震目录.再通过波形互相关震相检测技术标定地震事件在记录台站的震相到时,依据标定的震相到时,利用双差定位方法对震群进行精定位,基于地震精定位结果分析震群的震中扩展特征.最后通过波形互相关系数和破裂面重合程度检测震群中是否存在重复地震活动.通过计算共检测到目录遗漏地震事件103个.地震精定位结果显示发震构造为北东向断层,震中扩展表现出迁移速率先快后慢的两阶段线性扩展特征.震群活动期间共检测到两组重复地震活动,其中第一组发生在震中扩展的第一阶段,第二组发生在震中扩展的第二阶段.在三种常见的震群发震机理模型——级联触发模型、断层慢滑动模型和流体侵入模型中,断层慢滑动模型能够解释我们观测到的重复地震活动和震中线性扩展现象,因此认为此次滦县震群活动可能伴随断层的慢滑动,断层慢滑动可能对滦县震群的触发和持续活动起到一定作用.

The seismological mechanism of an earthquake swarm,a kind of seismic burst activity,means the physical and dynamic process in earthquakes triggering in the swarm.In the field of seismic activity research,detailed analysis of seismological mechanism of earthquake swarm is seriously important for understanding the process of earthquake triggering,moreover,which have been a hot spot in seismological research recent years.Here we focus on the seismological mechanism of 2015 Luanxian swarm in Hebei province based on the detailed analysis of digital seismic waveform record,and discus the relationship between observed phenomena and seismological mechanism models.The process of digital seismic waveform data processing is divided into four steps.（1）Choose the three components waveform of earthquakes which magnitude greater than M_L1.0 in the catalog as templates,and detect missing earthquakes by scanning the continues waveforms with matched filter technique.（2）Recalibrate P and S-wave phase arrival time using waveform cross-correlation phase detection technique to eliminate the artificial error in phase picking in the observation report made by Hebei seismic network,and then we obtain a more complete catalog and a more precise seismic phase report.（3）Relocate the earthquakes in the swarm using doubledifference method（hypoDD）based on phase arrival time we recalibrated,and analyze the characteristics of swarm epicenter migration based on the relocation result.（4）Detect whether there are repeating earthquakes activity using both waveform cross-correlation standard and whether rupture areas can overlapped.We finally detect 106 missing earthquakes in the swarm,66 of them have the magnitude greater than M_L0.0,include 2greater than ML1.0.Relocation result shows that the epicenters of earthquakes in the swarm have a strip distribution in NE-SW direction,which indicates the seismogenic structure may be a NE-SW trending fault.The spatial-temporal distribution variation of epicenters in the swarm shows a kind of two stages linear migration characteristics,in which the first stage has appeared with a higher migration velocity as 1.2km per day,and the velocity of the second step is 0.0024 km per day.Then we identify two classes of repeating earthquakes,the first class which have higher cumulative slip occurred in the first migration step,and the second class occurred in the second step correspondingly.According to the three basic models to explain the seismological mechanism of earthquake swarms：cascade model,slow slip model and fluid diffusion model,repeating earthquakes activity is difficult to explain by previous earthquakes stress triggering,however,it can be explained by continuing stress loading at the same asperity from fault slow slip.The phenomena of linear migration is more fitting slow slip model than the migration characteristics of fluid diffusion which satisfied diffusion equation.Comparing the phenomena we observed and the seismological mechanism models,we find that the Luanxian earthquake swarm may be associated with fault slow slip.Fault slow slip may play a role in Luanxian earthquake swarm triggering and sustained activity.