帕米尔东北侧地壳物性结构及其发震环境探讨  

STUDY OF CRUSTAL STRUCTURE IN TERMS OF PHYSICAL PROPERTY AND DISCUSSION ON SEISMOGENIC ENVIRONMENT IN THE NORTHEASTERN PAMIRS

作　　者：刘志[1] 张先康[1] 周雪松[1] 赵金仁[1] 张成科[1] 潘纪顺[1] 

机构地区：[1]中国地震局地球物理勘探中心,中国郑州450002

出　　处：《地震学报》2003年第3期242-249,共8页Acta Seismologica Sinica

基　　金：国家重点基础研究发展规划项目 (G19980 4 0 70 2 );国家重点科技攻关计划课题 (96 9130 7)

摘　　要：通过对帕米尔东北侧伽师及其周边地区两条深地震测深剖面S波资料的处理计算 ,结合P波研究结果 ,得到了S波二维地壳速度结构和波速比 (vP/vS)分布 .研究表明 :①塔里木块体平均地壳波速比明显高于西昆仑和天山褶皱带 ,显示了“坚硬”、稳定地壳物性特征 .下地壳正常偏低的波速比 (泊松比 )值 ,说明塔里木块体的“下插”是该地区地壳运动的主要特征 ;②天山褶皱带上地壳岩层相对较“软” ,易于在应力作用下断裂破碎和应力能量释放 ,是其小震密集分布的重要构造因素 ;③伽师附近正处在下地壳C界面和壳幔边界的上隆顶部或拐点上 ,是强震群发生的深部构造背景 .上地壳中下部的块体边界附近波速比值的交错变化和接触面复杂形态的存在 ,形成了伽师强震群出现的特殊构造环境 .震源处波速比相对较高 ,剪切模量较小 ,可能是伽师强震群应力降偏低的主要原因 .2-D crustal structure as well as velocity ratio ( v __P/ v __S ) is revealed by processing S-wave data from two wide-angle reflection/refraction profiles in and around Jiashi in the northeastern Pamirs, with the results of P-wave data taken into consideration. The result shows that: ① Average crustal velocity ratio is obviously higher in Tarim block than in West Kunlun Mts. And Tianshan fold zone, which reflects its crustal physical property of ″hardness″ and stability. The relatively low but normal velocity ratio (Poisson′s ratio) of the lower crust indicates that the ″downward thrusting″ of Tarim Basin is the main feature of crustal movement in this area. ② The rock layer in the upper crust of Tianshan fold zone is relatively ″soft″, which makes it prone to rupture and stress energy release. This is the primary tectonic factor for the concentration of small earthquakes in this area. ③ Jiashi is located right over the apex or the inflection point of the updoming lower crustal interface C and the crust-mantle boundary, which is the deep structural background for the occurrence of strong earthquakes. The alternate variation of v __P/ v __S near the block boundaries and the complicated configuration of the interfaces in the upper and middle part of the upper crust form a particular structural environment for the Jiashi strong earthquake swarm. v __P/ v __S is comparatively high and shear modulus is low at the focal region, which may be the main reason for the low stress drop of the Jiashi strong earthquake swarm.

关 键 词：S波二维地壳速度结构 波速比 地震测深剖面 发震环境 地壳运动 应力作用 伽师强震群 

分 类 号：P315.2[天文地球—地震学]