THE VARIATIONAL CHARACTERISTICS OF VP/VS RATIO IN SOURCE ZONE AND FIELD ZONE BEFORE AND AFTER THE HEZE MS. 9 EARTHQUAKE

In this paper, the VP/VS ratios of 148 earthauakes of M_L ≥ 2.0 occurred in the range of 34°30' 36°10' north latitude and 115°117°45' east longitude in 1979-1987 are calculated, the time and space variational characteristics of VP/Vs ratio in source zone and field zone and its difference before and after the 1983 Heze MS. 9 earthquake are analyzed and the calculated results are tested. The time and space variation of Vp/Vs ratio in source zone and field zone and the tested result show that before the M5.9 earthquake the Vp/Vs ratio in source zone showed a clear process of decrease-low walue-recovering The field zone showed a low value anomaly immidiately before the M5.9 earthquake. The calculated result of the Vp/vs ratio in source zone and field zone is consistent after the M 5.9 earthquake, both time and space variations are normal.