地电场水文地质因素及裂隙水主体渗流方向逐日计算

Hydrogeologic factors of geoelectric field and diurnal computation of preferred orientation of crack water seepage

2007年西昌和天祝地电场观测台阵建立,随后两年西昌台阵地电场的TGF-A波形明显,天祝台阵则以TGF-B波形出现.台阵内各台站间地电场相关性高,这受地电场潮汐机理的支持;不同台站或同一台站的不同方向地电场潮汐波峰谷值差异明显,地电场潮汐机理和场地水文地质资料表明,这主要与岩石、裂隙度、裂隙优势走向、含水度、透水率、水矿化度和裂隙水压力差等因素相关.潮汐电信号形成于裂隙水或水中电荷周期性移动,电荷被岩壁吸附或脱离产生噪声,该信噪比在同一台阵内基本相同,信噪比值与潮汐电信号产生过程和场地电磁背景关系密切.应用地电场潮汐谐波振幅计算裂隙水主体渗流方向,结果与应用潮汐波峰谷值法基本一致,这消除了峰谷值法取值的偶然误差.2008年汶川MS8.0地震前,两台阵内都存在场地裂隙水主体渗流方向的短临变异现象,西昌台阵这种变异更明显.

Xiehang and Tianzhu geoelectric field observational arrays were set up in 2007. In the following two years, TGF-A waveform appeared obviously in Xiehang array, while TGF-B waveform was observed in Tianzhu array. Geoelectric fields at different stations in either of the arrays were highly correla- ted, which was supported by tidal mechanism of geoeleetrie fields. Tidal peak- to-trough values at different stations or in different orientations of the same station are obviously different, and this is closely related to such factors as rock characteristics, degree of cracking, preferred orientation of cracks, water ratio, seepage rate, degree of water mineralization and pressure difference of crack water, according to tidal mechanism and hydrogeologie data. Tidal electrical signals come from periodic movement of crack water or electric charge. When charge is adsorbed to rocks or breaks away from rocks, noise is produced. The signal-to-noise ratio appears almost identical within the same array, and it is closely related to the signal generating process and electromagnetic background on the site. Tidal harmonic amplitudes were used to compute preferred orientation of crack water seepage, which yielded the same result as with peak-to-trough value method, avoiding accidental error caused by taking peak and trough values. Before the Wenchuan Ms8. 0 earthquake in 2008, there were short-term and impending variations of preferred orientation of crack water seepage in both of the arrays, but more obvious in Xiehang array.