Bedrock structure related to active faults in Lijiang basin, Yunnan, China, and its seismic microzoning

1996年丽江7.0级地震给丽江盆地带来了严重的破坏。其发震断层虽然被认为是位于沿着盆地西缘的雪山断裂，但破坏最严重的地段位于距盆地边缘1.5 ~ 2km处，而在盆地南部穿越盆地的丽江-剑川断裂带的沿着附近，破坏程度有明显变化。作为小区划问题，进行了重力测量和地质研究，以揭示与活动断裂相关的基岩结构。建立了丽江盆地、邻近的拉什盆地和南部的鹤庆盆地的三维重力基底模型。每个盆地到基岩的深度超过2km。对卫星图像进行了分析，以绘制在现场检查的活动断层。GPS观测是为了监测与断层有关的地壳运动。根据区域构造控制下的拉分构造，探讨了北方盆地的构造特征及其成因。破坏的异常分布应归因于与断层相关的基岩配置与陡峭的起伏（盆地边缘效应和/或聚焦效应），并在沉积物中的断裂带的地质条件。

The 1996 Lijiang Earthquake of M7.0 brought serious damage to the Lijiang basin. Although its seismogenic fault is considered to be the Xueshan fault lying along the western edge of the basin, the most severely damaged zone was located 1.5-2 km far from the basin edge, and there was a remarkable change in degree of damage near along the Lijiang-Jianchuan fault zone, which crosses the basin in the southern part. As an issue of microzoning, gravity survey and geologic study were conducted to reveal the bedrock structure associated active faults. 3D gravity basement was modeled for Lijiang basin, adjacent Lashi basin, and Heqing basin ranging south. The depth to bedrock reaches more than 2km for each basin. Satelite images were analyzed to map active faults which were checked in the field. GPS observation was carried out to monitor the crustal movement associated the faults. The basins structure and its genesis were discussed on the basis of pull-apart structure controlled by the regional tectonics in northern Yunnan. The anomalous distribution of damage should be attributed to the fault-related bedrock configuration with steep relief (basin-edge effect and/or focusing effect), and to the geological condition of fault zone in the sediments.