张北地震区三维构造特征

地震层析成像结果揭示了张北地震区的构造特征。震源区周围分布有相交的北北西和北东向低速异常带。极震区正下方壳内存在高速异常的坚固体 ,其周围被多条低速异常带围限。区域构造具备了大量积累应变能和向高应力区传递应变能的孕震构造特征 ,北北西和北东向的隐伏断裂共同构成了区域的发震构造。该震区在中新生代以来有过多期岩浆活动 ,震中区周围分布有几个新第三纪的火山口。极震区米家沟附近火山的三维剖分图给出了该火山从地表到壳内 10km深度的速度图像 ,中新生代的火山岩浆活动对该区域孕震构造的形成起了重要作用。

3-D STRUCTURAL FEATURE IN ZHANGBEI EARTHQUAKE REGION

Result of tomography reveals the structural features of Zhangbei earthquake region. There exist two low velocity zones intersecting each other in focal region, one trending NNW and the other NE. And there exists a solid block in the crust below the meizoseismal area, which is enveloped by several low velocity zones. Regional tectonics possess earthquake development features, accumulating mass strain energy and transmitting strain energy to nearby high stress region. The seismogenic structure in this region is composed of two blind faults, one trending NNW and the other NE. There are multiphase magmations during Meso-Cenozoic in this regions. And there are several Neogene craters around the epicentral region. 3-D imaging of the volcano lying in the meizoseismal area nearby Mijiagou has shown the velocity structure from surface to 10 km depth for this volcano. The magmation of Meso-Cenozoic plays an important part in the formation of seismogenic structure.