强地震附近视电阻率各向异性变化的原因  

A possible reason for the anisotropic changes in apparent resistivity near the focal region of strong earthquake

作　　者：杜学彬[1] 李宁[1] 叶青[2] 马占虎[1] 闫睿[3] 

机构地区：[1]中国地震局兰州地震研究所,兰州730000 [2]中国地震台网中心,北京100036 [3]北京市地震局,北京100080

出　　处：《地球物理学报》2007年第6期1802-1810,共9页Chinese Journal of Geophysics

基　　金：国家科技支撑计划课题(2006BAC01B02-04-03);国家自然科学基金(40474027);中国地震局地震联合基金(102058)共同资助

摘　　要：讨论了强地震、孕震晚期阶段、震源区及附近介质的物理变化过程,证明了视电阻率变化最显著的方向与最大加载方向之间的正交关系,建立了真、视电阻率各向异性变化与裂隙率ν、骨架电阻率ρo、饱水裂隙电阻率fρ的本构关系,解释了视电阻率各向异性变化的原因.研究认为:在强地震孕震晚期阶段,在震源区及附近地壳近地表的较深部,介质微裂隙发育,其走向沿最大主压应力方位优势取向,低阻水充填微裂隙,导电通道连通,引起最大主压应力方向真电阻率变化最显著的真各向异性变化,从而产生垂直主压应力方向视电阻率变化最显著的视各向异性变化,低阻水在其物理过程中起了显著作用.In this paper, we discussed the physical processes of the medium in/near the focal region in the late preparation period of strong earthquake, theoretically proved the orthogonal relation between the maximum loading direction and the direction of most prominent change in apparent resistivity, and produced the constitutive relations of anisotropic changes in true resistivity and apparent resistivity to crack ratio v, crackwater resistivity ρf and framework resistivity ρο, and then proposed a possible reason for the anisotropic changes in apparent resistivity. We consider that in/near the focal region in the late preparation period of strong earthquake, the micro-cracks in the crust medium develop fast in number and size, which strike predominantly along the maximum compressional stress orientation of focal mechanism solution, and then the low resistance crack-water comes fast in and conductive aisles connect each other. The anisotropic changes in true resistivity, in which the most prominent change is maximum compressional stress orientation, and the true anisotropic changes physical processes generate in the direction in or close to cause the anisotropic changes the the in apparent resistivity, in which the most prominent change is in the direction perpendicular or nearly perpendicular to the orientation. The underground water with low resistance plays a very important role in the above physical processes.

关 键 词：强地震 孕震晚期 视电阻率 各向异性变化 震源机制解 

分 类 号：P315[天文地球—地震学]