Research On Repeated Seismic Detection And Precise Positioning In The Anninghe Fault Zone

The Anninghe fault zone(AFZ)is one of the most important faults on the east boundary of the Tibet block.Compared to other parts of China,this fault zone and its surrounding areas show significant tectonic deformation with high seismicity.The fault slip rate,especially at the deep part,plays an important role in studying the characteristics of the fault motion and the risk of large earthquakes.Although the paleo-seismic profiles can be used to obtain the past slip rate in depth and geodetic techniques are usually to determine the slip rate on the surface,the current slip rate in depth cannot be obtained.In addition,the small earthquake locations from regional seismic network show that there is an earthquake gap of about 170 km in the middle section of the AFZ.Due to the poor location and monitoring capabilities of the sparse regional network,the existence of seismic activity in this gap remains to be further verified.In this paper,the template matched filtering(MFT)method is used to investigate the seismicity of the AFZ,while the identified repeating earthquakes are used to estimate the slip rate in depth.The MFT method utilize the waveform similarity between earthquakes,the waveform cross-correlation method,to detect seismic events in continuous waveforms.Repeating earthquakes refer to a group of earthquakes that occur at the nearly same location of the fault and have a constant recurrence interval.They are usually considered from the rupture of small asperities.First,we collecte the continuous waveform data of 32 stations in the Xichang Array from 2013.1-2019.5and the P and S-wave arrival times dataset of 9,386 events.Secondly,based on the signal-to-noise ratio analysis for event waveforms,3,740 template events were selected.A total of 77,993 earthquake events are detected,which greatly expanded the routine catalog.Then,the waveform cross-correlation calculation is carried out for the identified earthquakes whose epicenter distance is smaller than 10 km,and similar earthquake pairs are obtained and grouped.After relocation and calculation of the size of the rupture zone,12 groups of repeated earthquakes are obtained.The result shows that based on the Xichang dense array and MFT method,a relatively complete catalog in the study area has been obtained,which reveals the seismic in accepted event gaps.In addition,there are multiple sets of repeating earthquakes in the gap,such at Shimian,Mianning and southern Xichang on the AFZ.It suggests that there are small asperities in this area,and repeating ruptures release the accumulated stress and strain.Also,the slip rate of AFZ in depth is calculated,which provides seismological evidence for the analysis of large earthquake risk in the study area.