南北地震带南段地震构造运动特征

Seismo-tectonic motions in the southern segment of the North-South Seismic Belt

本文使用地震资料研究了青藏高原与华南块体边界南北地震带南段的地震类型及其构造运动的区域特征.发现金沙江上游东侧与鲜水河南侧之间的正断层型地震活动区,存在南北向扩张的地震构造运动;金沙江下游东侧正断层型地震活动区存在东西向扩张的地震构造运动.在龙门山断裂及其西北相邻地震带是一个逆断层型地震活动区.其他地区多为走滑型地震.南北地震带南段东西两区域地震应力场主压应力P轴方向呈现区域性差异.南北地震带南段西部区域的应力场主压应力P轴的方向大部都沿北东-南西方向分布,这与青藏高原地区的主压应力P轴的方向分布一致.南北地震带南段东部区域的主压应力P轴的方向大部都沿北西-南东方向分布,与华南地区的应力场大致相同.南北地震带南段东、西两区主压应力P轴方向所呈现出的不连续性分布特征,表明了南北地震带南段东部区域的地震孕力场可能是另有一个北西-南东方向分布的孕震力源的应力场.它可能与台湾纵谷断层地区菲律宾海板块北西向挤压的构造应力场有关.

The seismogenic tectonics and stress fields in the southern segment of the North-South Seismic Belt（ NSSB） in the boundary between the Tibetan Plateau and the Southern China blocks（ BTPSC） were analyzed employing seismic data. The finds suggest that a normal faulting type earthquake region exists east of the Jinshajiang fault. The normal faulting of earthquake resulted in extensional motion along north-south direction east of the upper reaches of the Jinshajiang. This is a new discover differently from the classic eastward escape in the eastern edge of the Tibetan plateau. The normal faulting of earthquake resulted in extensional motion along east-west direction east of the lower reaches of the Jinshajiang. The thrust faulting type earthquake region exists in the Longmenshan fault with NE-SW strike direction and its northwestern vicinity. The many strike-slip faulting earthquakes occurred other regions. The principle compressive stress axes（ P axes） of focal mechanisms align almost in the NE-SW direction in the western region of the southern segment of NSSB in the boundary between the Tibetan Plateau and the Southern China Blocks. This direction coincides to the P axes direction in the Tibetan plateau. The P axes of fault plan solutions, however, array almost in the NW-SE direction in the eastern region in the boundary between the Tibetan Plateau and the Southern China blocks. This direction coincides to that of P axes in the southern China block and Taiwan region. The P axes in the eastern region crossed with those in the western region and formed some angles in the southern segment of NSSB. Such P axis crossing between the eastern and western region imply that the seismogenic stress field with NW-SE direction in the eastern region does not generate from the simply obstructing the eastward motion of the Tibetan plateau. The seismogenic stress field with NW-SE direction probably has its independent source for such P axis direction in the eastern region of BTPSC. It may come from the westward collision and subduction from the Philippine Sea plate in the Taiwan region and Ryukyu arc.