基于视出射角与到时参数联合定位方法对高邮、宝应交界M4.9地震序列的定位研究

Location of the Gaoyou-Baoying M4.9 Earthquake Using Apparent Emergence Angle and Seismic Arrival Times

摘要:

利用P波视出射角与到时参数对2012年7月20日江苏高邮、宝应交界M4.9地震序列进行了联合定位。建立了与视出射角联合定位方法的目标函数，并使用蒙特卡洛法进行反演计算。结果表明地震序列沿杨汊苍—桑树头断裂带呈NNE向密集型分布；深度分布显示断层以走滑为主，带有少量正断，高倾角特征；结合速度结构，地震序列集中发生在速度高值区和低值区的交界部位，即脆—韧性转换带，并且震源深度的下界面止于20 km。根据速度结构性质认为下部地壳的高速结构为其提供了上部地壳横向运动的松弛边界条件。

Abstract:

An M4.9 earthquake occurred in Gaoyou-Baoying，Jiangsu on July 20，2012.Numerous aftershocks followed the main shock.According to the China Earthquake Networks Center，there were 84 aftershocks with a magnitude of 1.0 and above until July 30，2012；there were 59 aftershocks with a magnitude of 1.0~1.9，20 with a magnitude of 2.0~2.9，4 with a magnitude of 3.0~3.9，and one with a magnitude of 4.0~4.9.In this study，84 aftershocks from July 20 to July 30，2012 were precisely located using the Multiparameter Seismic Location method.The apparent emergence angles and arrival times were extracted according to the wave data with SEED format.The objective function in the Multiparameter Seismic Location method using apparent emergence angles and arrival time was determined.The Monte Carlo method was used to realize its optimization.The apparent emergence angle has a very strong sensitivity to depth.The results of the Multiparameter Seismic Location method are accurate with respect to latitude and longitude，and in particular，enhance the depth resolution effectively.This study used the Multiparameter Seismic Location method to determine the location of the aftershocks of the M4.9 earthquake at the border area between Gaoyou and Baoying.The apparent emergence angles and arrival times were extracted according to the wave data.The results of the Multiparameter Seismic Location method show that the earthquake sequence was densely distributed along the Yangchacang-Sangshutou fault zone，in a spatial belt with a NNE direction.The average depth of the earthquake sequence is 12.21 km，distributed in a range of 5~20 km （up crust），but the dominant distribution is at 12~15 km.The depth of the M4.9 earthquake was at 9.3 km.The depth distribution is more at the strike slip region，where there is a small amount of thrust coming from the detachment plane （belt）at a depth of 12~15 km.The aftershocks are densely distributed at the fault ramp，which is the region of stress accumulation；the main shock occurred at this location.The high speed structure of the lower crust provides a relaxed boundary condition for transversal motion.The depth is concentrated at the brittle ductile transition zone，which is the speed boundary between the high- and low-values，at a depth of approximately 20 km.The different thickness of the lower crust caused the great changes in the earth’s crust.Subei thickness thinning may have contributed to the deep dynamic environment.The results of the Multiparameter Seismic Location method show that the earthquake sequence is densely distributed along the Yangchacang-Sangshutou fault zone.