自然电场的区域性变化特征

Features of regional variations of the spontaneous field

以场源为分类原则,地电场E由自然电场ESP和大地电场ET构成.ESP起源于地下介质物理、化学作用,通常其变化及稳定性具有明显的局部场地特征;ET起源于空间电流系和潮汐力,在日变波形、频谱特征上表现出广域性.在形成微观机理方面,ESP和ET能够具有部分相同的机理过程.2008—2013年,在南北地震带附近13个代表性场地,多数ESP不具有清晰的年变波形,其稳定性也受区域、场地、方位、构造活动等因素影响.在这些地区,ESP较平稳的持续升降、快速跃变、突跳等现象常见,同一主断裂带附近或局部区域内,这些大幅变化的趋势转折点多具有时间同步或准同步性,同一时段数据稳定性可能类似,但形态变化存在场地因素而不具相关性.ESP较平稳期间,应用潮汐地电场频谱特征计算的裂隙水主体渗流方位α易处于相对稳定状态,而在其剧烈变化期间的α常会明显变化.以潮汐地电场频谱特征逐日计算α值,可能揭示场地裂隙、裂隙水渗流、主压应力的逐日变化信息,进而可解析ESP、ET宏观变化的微观机理过程.

According to the classification principle of field sources, the geoelectric field E is composed of the spontaneous field Esp and telluric field ET. The Esp originates from physical and chemical actions of underground media. Its change and stability have usually obvious characteristics of local sites. The ET originates from the space current system and tidal forces, and shows the nature of broad areas in diurnal variation waveforms and spectral characteristics. In respect of the microscopic mechanisms of their formations, the Esp and ET can have partial same processes of mechanisms. In 2008--2013, in the vicinity of the north-south seismic zone in China mainland, the data of representative 13 geoelectric field observatories suggest that the Esp of most sites do not exhibit clear annual variation waveforms, and their stabilities depend on regions, sites, orientation, tectonic activity and other factors. In these areas, among the variation forms of the Esp, phenomena are common like relatively steady rises and falls, rapid jumps, sudden jumps and so forth. In the vicinity of major faults and local areas, the trend turning points of these big variations often show the features of temporal synchronization and quasi-synchronization. The data stability may be similar at the same period of time, while its form variations are usually irrelevance for site factors. During the more steady phase of the Esp, the preferred orientation α of crack water seepage calculated by the application of spectral features of tidal geoelectric field tends to be in a relatively stable state; during extreme fluctuations of the Esp, the a often experiences significant changes. The a calculated on a daily basis according to the spectral characteristics of the tidal geoelectric field may reveal the daily variation information of fissures, crack water seepage, principal compressive stress of the site, which thus can help analyze the process of microscopic mechanisms of macro changes of the Esp and ET.