天祝-古浪地震剪切波分裂及电性各向异性变化特征

TEMPORAL EVOLUTION OF THE SHEAR-WAVE SPLITTING AND THE GEO-ELECTRICAL ANISOTROPY IN TIANZHU-GULANG EARTHQUAKE

摘要:

采用与永登地震相同的方法,研究了1996年6月1日天祝-古浪5.4级地震前后地壳介质剪切波分裂、电性各向异性随时间的变化特征.结果表明临震前电性主轴、快S偏振方向都是从北偏西方向转为北偏东,而该次地震的P轴为北偏东50°,三者总体上是一致的.由于该次地震与松山电磁台同处一个断层构造上,因此视电阻率变化在各频段均较强,但ρ_yx比ρ_xy变化大,这一点与永登地震不同.另外,由于收集的小震资料较少,快慢S波时间延迟的分析结果没能反映出应力强度的积累,另一个原因可能是该次地震孕育与永登地震后应力调整纠缠在一起的结果(两者距离120多公里).

Abstract:

Adopting the same method used in the study on Yongdeng earthquake^[1],the temporal evolution characteristics of shear wave splitting and the geo electrical anisotropy of crust media during the preparation and occurrence of Tianzhu-Gulang M_S5.4 earthquake on June first, 1996 are studied.The results show that before the earthquake both the geo electrical axis of ρ_xy and the polarization of fast S wave rotated from northwest to northeast until occurrence of the earthquake,its source mechanism solution indicats that the P axis direction is in N 50°E. So the three directions are generally the same.On the other hand,the geo-electrical station is coincidently on the seismogenic fault, the variations of apparent resistivity of various frequencies are all evident while the variation of ρ_xy component is greater than ρ_xy component contrary to that of Yongdeng earthquake. But due to scarce of collected seismic data the accumulation process of stress is not demonstrated by the time delay between the two split S waves. The other reason for the analyzed result of time delay maybe is the influence of stress adjustment after Yongdeng earthquake on the stress preparation of Tianzhu-Gulang earthquake (the distance between two events is about 120 km).