摘要
Abstract
An M 4.9 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 after-shocks 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. <br> 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 Multipa-rameter Seismic Location method using apparent emergence angles and arrival time was deter-mined.The Monte Carlo method was used to realize its optimization.The apparent emergence an-gle 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. <br> This study used the Multiparameter Seismic Location method to determine the location of the aftershocks of the M 4.9 earthquake at the border area between Gaoyou and Baoying.The ap-parent 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. <br> 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 M 4.9 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. <br> The high speed structure of the lower crust provides a relaxed boundary condition for trans-versal 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 Seis-mic Location method show that the earthquake sequence is densely distributed along the Yangchacang-Sangshutou fault zone.关键词
高邮/宝应交界 4.9 级地震/视出射角/地震波到时/联合定位Key words
Gaoyou-Baoying M 4.9 earthquake/apparent emergence angle/seismic arrival time/multiparameter seismic location分类
天文与地球科学
