汶川地震破裂带断层岩纵波速度与孔隙度关系的实验研究  

Experimental studies on relationship between P-wave velocity and porosity of fault rocks from the rupture of the 2008 Wenchuan earthquake

作　　者：杨彧[1] 陈进宇[2] 杨晓松[2] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]地震动力学国家重点实验室,中国地震局地质研究所,北京100029

出　　处：《地球物理学报》2014年第6期1883-1890,共8页Chinese Journal of Geophysics

基　　金：地震动力学国家重点实验室团队课题(LED2010A03);国家科技专项汶川地震断裂带科学钻探(WFSD-09);国家自然科学基金(41372202)共同资助

摘　　要：分布于地震破裂带上的断层岩具有高孔隙度的特征.该特点造成了其弹性波速度与结晶岩石和沉积岩存在明显的差异.确定断层岩的弹性波速度与孔隙度和矿物组成的关系对于利用地震资料探测深部断层和测井资料的解释至关重要.在10-600 MPa条件下,本文对地震断层岩的纵波波速（V_p）和总孔隙度（φt）进行了测量,并深入分析了Vp与孔隙度的关系.结果表明在10-600 MPa的压力范围内,V_p（p）随着压力的增高呈现对数增加,其增长率随着压力的上升而逐渐减小,遵从φVp（p）/ p=a_v/p的变化规律.断层岩中的孔隙度随着压力的增高呈对数减小.与传统的认识不同,实验发现在压力高达600 MPa以上,大多数断层岩中仍然可以残留可观的孔隙量.分析显示Vp与总孔隙度及总粘土含量呈负线性相关.该发现有助于认识深部流体的活动通道特征,有助于理解断层带中存在大量粘土矿物、断层带内的物质可被大量带出、围陷波的形成等地质和地球物理现象.The seismogenesis fault rocks are characterized by high porosities which causes significant deviation in elastic wave velocities between them and crystallized rocks.Experimental studies on the relationship between the velocities and pores and mineral contents can provide effective constraint on interpretation of logging and seismic survey data.The P-wave velocity（V_p） and total porosity（φ_τ） of fault rocks from the rupture zone of the 2008 Wenchuan earthquake,China,were measured at pressures ranging from 10MPa to 600 MPa and room temperature.The results indicate that compressional wave velocity rises logarithmically with increasing pressure and the rate of velocity increasing becomes smaller and smaller with pressurization,dV_p（p）/（？）p = a_v/p.Meanwhile,the total porosity drops logarithmically with pressurization.An interesting phenomenon is that pores can survive in fault rock specimens even when pressure reaches 600 MPa.Compressional wave velocity of the fault rocks is inversely associated with total porosity and clay mineral contents.The results provide insight into fluid flowing in deep crust,understanding of formation of clay minerals within fault zone and element migration along fault belt,and interpretation of trapped wave in Wenchuan earthquake region.

关 键 词：P-波速度 孔隙度 汶川地震断裂带 实验研究 

分 类 号：P545[天文地球—构造地质学]