通州台井下地电阻率测深初步分析

2020年7月12日唐山古冶 M_S5．1地震发生前,井下小极距地电阻率出现快速下降-折返的变化,变化形态、异常时长符合地电阻率孕震机理变化,但下降幅度远远小于地表大极距地电阻率孕震过程的变化幅度.因此,文章基于通州台地下电性结构和装置系统,采用数值分析方法,分析地表和井下小极距地电阻率的探测深度.结果表明,当底层电性变化区域介质电阻率发生某种减小时,通州台地表和井下小极距地电阻率装置系统地电阻率观测值会下降,下降的幅度随着深部介质电阻率变化区域上界面向上的扩展而增大.相比地表观测,井下小极距电阻率观测能更显著地接收到深部电阻率变化信号,对孕震有更强的反映能力.

Preliminary study on deep\|well geoelectrical resistivity sounding at Tongzhou station

Before the Guye M_S5.1 earthquake in Tangshan on July 12, 2020, the short-electrode-spacing deep-well geoelectrical resistivity showed a change rapid decrease-return phenomenon. The variation pattern and anomaly duration conform to the seismogenic mechanism of geoelectrical resistivity, but the decreasing amplitude is far smaller than that of the seismogenic process of large polar distance geoelectrical resistivity. Therefore, based on the underground electrical structure and device system of Tongzhou station, this study used the numerical analysis method to analyze the detection depths of ground resistivity and short-electrode-spacing deep-well geoelectrical resistivity. The results show that when the resistivity of the medium in the bottom layer decreases, the observed value of the ground resistivity and short-electrode-spacing deep-well geoelectrical resistivity at Tongzhou station will also decrease, and the decreasing range increases with the upward expansion of the upper interface of the deep medium resistivity change area. Compared with the observation of surface resistivity, the short-electrode-spacing deep-well geoelectrical resistivity observation can receive deep resistivity change signals more significantly, thus having a stronger ability to reflect earthquake preparation.