用深地震反射方法研究邢台地震区地壳细结构

A STUDY ON FINE CRUSTAL STRUCTURE IN XINGTAI EARTHQUAKE AREA BASED ON DEEP SEISMIC REFLECTION PROFILING

为了取得邢台地震区的地壳细结构,1990年冬,国家地震局地球物理研究所等实施了一条穿过华北平原中部束鹿断陷盆地的深地震反射剖面.经过叠加和偏移后的剖面显示出清晰的地壳细结构图像.剖面图上1—4s之间的强反射对应于由一组正断层产生的沉积层变形,其中新河断裂为束鹿盆地和新河凸起之间的边界主断裂,它伸展到8km以下深处.在5s左右显示出一组较强的反射界面,它可能对应于脆性上地壳的下界面.10—11s之间的壳-幔过渡带包含一组振幅大、连续性好的强反射,在震源下方的Moho界面上似乎被间断.岩浆从上地幔顶部侵入到地壳中,使得地壳可能出现部分熔融,这一过程是产生扩张盆地和发生邢台地震的主要原因.

Xingtai earthquakes of 1966 are located in the Shulu fault basin and its neighbor in the central region of North China Plain. In order to reveal the fine crustal structure in the earthquake area, a deep seismic reflection profile passed through the fault basin was conducted in the winter of 1990. The seismic section after stacking and migrating shows clearly the image of the fine crustal structure. On the section, strong reflections in 1-4 s TWT correspond to the deformation of sedimentary layers produced by a set of normal faults, where Xinghe fault is the main boundary fault between Shulu basin and Xinghe uplift, and extends to 8 km deep. The reflections at about 5 s may be correlated to the lower boundary of the brittle upper crust. The crust-mantle transition in 10-11 s contains a set of strong reflections with high amplitude and well continuity. However, it seems to be discontinuous beneath the hypocenter. The injection of magma from uppermost mantle to crust and partial melting of the lower crust may occur in this zone. This process may produce the extensional basin and the strong earthquakes.