The Earthquake Sequence And Shear Wave Splitting Of Jinggu Area

Using the double difference location method,seismogram 8219 M?1 in the Jinggu area(99.2 ° E ~ 101.2 ° E,99.2 ° N ~ 24.5 ° N)coverage of nine stations were recorded?The E-W direction positioning error is 12 m,the N-S direction positioning error is 17 m,the vertical error is 23 m,the root mean square residual of the arrival time difference is 0.01 s.This paper has analyzed the Jinggu seismic sequence by double-difference location,the results of 1425 earthquake relocations were obtained,the E-W direction positioning error is 34 m,the N-S direction positioning error is 78 m,the vertical error is 47 m,the root mean square residual of the arrival time difference is 0.145 s.The reorientation of the earthquake in the whole area showed the distributions of the epicenter were more concentrated after relocation,closer to the fracture zone,the dominant distribution region is within 10 km on both sides of the fracture;the distribution of focal depth is more connected,the focal depth of the vast majority of seismic events distributed in 0-20 km.The Relocation result of Jinggu Ms6.6 earthquake showed,the distribution of the epicenter was more concentrated,the horizontal direction showed a clear band distribution trend.In the vertical direction,the depth distribution of seismic sequence was linear,It was mainly concentrated in a linear region of northwest-southeast.The distribution of aftershocks was relatively discrete in the early stage,and then gone to quickly focus on the linear distribution.The main fracture areas of the earthquake are linear,approximately N-W direction,the depth of the northwest part was shallow,the closer to the southeast part was deeper.Between June 2009 and February 2015,there were over 30,000 earthquakes in the area,with an average of 441 per month,after the Jinggu earthquake,there were3,241 earthquakes in total,with an average of 1,600 times a month.Between December 7,2014 and February 1,2015,there were 1000 earthquakes,In the periodafter the earthquake,the energy stored in the seismogenic structure of the area was released to a certain extent,which greatly reduced the frequency of the earthquake.Using SAM method to analyze the earthquake of M ? 1 in the area,there 101 earthquake shear wave splitting parameters of the 9 stations were obtained.Comparing different stations of shear wave splitting result,found the advantages of fast shear wave polarization direction may be similar the nearly fault,the station far away from the fault,the stress field of the crustal structure under the station is more similar.The wave polarization direction and slow wave time delay between before and after the Jinggu earthquake showed the result,the polarization direction of the fast wave was clear and concentrated before the earthquake,anisotropy is obvious;after the earthquake,the direction of fast wave polarization was more discrete and the time delay becomes smaller.It was indicated that the earthquake near the station will have a certain effect on the medium under the station.