摘要
本文研究了兴都库什及帕米尔地区地震的空间分布.发现h<70km的地震分布广泛,h≥100km的地震形成—S形的倾斜中源地震带.在71.5°E以西,中源地震带倾向接近正北,倾角随深度变化,在深部接近垂直,且倾角自西向东逐渐变陡,在71.5°E以东,倾向逐渐由东南变为正南. 分析了121个m_b≥5.0地震的机制解.浅源地震机制解的P轴大多位于NS和NNW—SSE方向,且多近水平,反映此区受到NS或NNW—SSE方向挤压.各剖面应力轴分布规律性强,在150km以下,总的趋势是机制解的T轴接近于倾斜的中源地震带的下倾方向,而P轴倾角较小且垂直于倾斜的中源地震带的走向.
The distribution of earthquakes of Mb ≥ 4.0 in Pamir-Hindukush Regions was studied using the data from I.S.C. for the period from 1968 to 1982. The earthquakes which are shallower than 70 km formed four seismic belts striking from NE to SW. The earthquakes deeper than 100 km concentrated in a S-type belt which is about 700 km long. Series of cross sections perpendicular to the deeper seismic belt were taken. It is shown that the intermediate earthquakes formed an obvious and oblique seismic zone. In the west of 71.5°E, the dip direction of the zone is due North, the dip angle changes with depth and is nearly vertical below the depth of 150 km. The dip angle becomes larger gradually from West to East, the earthquakes deeper than 200km occured mainly in this zone. In the East of 71.5°E, the dip direction of the oblique seismic zone changes gradually from ES to due south. Few of earthquakes deeper than 100 km occured in East of 75.8°E.Eighty one fault plane solutions for earthquakes of Mb≥5.0 were obtained using the first motions of P wave. The stress state in this region were studied using the fault plane solutions obtained by this paper and other authers. The P axes for earthquakes shallower than 70 km are mostly in the North-South direction and nearly horizontal, it reflects that the crust is under North-South or NNW-SSE compression, the distribution of P axes for shallow earthquakes have obvious influence from the local tectonic movement. There are clear characteristics for the distribution of the axes of stresses in the oblique intermediate earthquake zone. In general, the T axes are nearly vetical and P axes are nearly horizontal; below 200 km, the directions of T axes are coincidant with that of the oblique seismic zone and P axes are perpendicular to the strike of the oblique seismic zone. The results shown that the distribution of shallow earthquakes may be correlated with the large faults, but the intermediate earthquakes may be correlated with some remains of subducting ocean slab.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
1990年第6期657-669,共13页
Chinese Journal of Geophysics
关键词
地震
空间分布
应力场
帕米尔
Stress field, Seismic belt, Pamir-Hindukush regions.
