上海及邻近地区区域应力场和地震破裂方式的探讨

DISCUSSION OF STRESS FIELD AND EARTHQUAKE RUPTURE FORM IN SHANGHAI AND ITS NEIGHBOURING REGION

本文从震源机制、地应力测量、地震等震线长轴统计,形变场、构造分析等几方面求得本区区域应力场在北纬30°以北为81°,30°以南为133°。空间分布上主压应力轴大致与海岸轮廓线垂直,反映力源主要来自太平洋板块对中国大陆的挤压。在这样的应力场背景下,本区北东向断裂将作右旋正走滑活动;北西向,特别是北北西向新断裂将作左旋逆走滑活动;北东东至近东西向断层将作张性倾滑活动。由于本区地震大多座落在不同方向断裂的交汇复合部位,地震的孕育、发生、发展与两断裂的共轭活动关系密切,但具体到某一次地震的破裂方式则以单侧破裂与双侧破裂居多。

According to the source mechanism, the ground stress measurement, the major axis statistics of isoseismal, the deformation field and the tectonic analysis etc, the regional stress field was determined in this paper to be: 81°with the North Lati- tude large than30°and 133°with the North Latitude less than 30°. The prin cipal compression axes of spatial distribution are roughly perpendicular to the sea coast line, showing that the source force comes mainly from the compression the Pacific plate. Under such stress field, the local NE fault takes the form of right-lateral normal striking-slip motion. The NW fault, especially the NNW neo-fault, takes the form of left-lateral inverse striking-slip motion. The NEE to E fault takes the form of tension dipslip motion. Since most of the local earthquakes occurred in the intersection region of different faults, the pregnancy, occurcence and the development of earthquakes had a close relation with the conjugate motion of faults. As to the rupture mode, most earthquakes took the single-lateral rupture or bilateral mode.