京津唐渤和周围地区地壳上地幔电性结构及其与地震活动性的关系

京津唐渤及其周围地区是我国的强烈地震活动区之一。自1976年以来,我们在该区开展大地电磁测深工作,完成了近30个测点。所得结果表明,本区壳内存在高导层,与地震方法确定的壳内低速层一致。平原内上地幔高导层埋深50—80公里,山区大于100公里,与地震方法确定的上地幔低速层基本一致,同时与大地热流测量、居里等温面计算和对新生代玄武岩地球化学研究结果基本吻合。本区绝大多数地震位于壳内高导层之上,强烈地震主要发生在上地幔高导层隆起的边缘。最后讨论了本区强震活动与壳内和上地幔高导层的关系。

THE ELECTRICAL STRUCTURE OF THE CRUST AND UPPER MANTLE AND ITS RELATIONSHIP WITH SEISMICITY IN THE BEIJING-TIANJIN-TANGSHAN REGION AND ADJACENT AREA

The Beijing-Tianjin-Tangshan region and adjacent area are one of strong earthquake region in China and technically have undergone intense disturbance resulting in uprise of surrounding mountain regions and intensive fracture and subsidence of the plain since Cenozoic age. MT measurements at 30 sites have been carried out since 1976. Data of MT were processed by the tensor impedance method and the apparent resistivity curves of E polarization were fitted to 1-D models for obtainning the electrical structure of the crust and upper mantle. The results of interpretation indicate that within the intermediate crust,there widely exists a high conductive layer with thickness of several km and resistivity from several to more than ten Ωm,and it corresponds to the low velocity layer in the crust determined by DSS; a high conductive asthenosphere with resistivity of one to several Ωm lays at a depth from 50 to 80 km beneath the plain and at a depth of more t han 100 km in the surrounding mountain regions,and it corresponds to the low velocity layer in the upper mantle determined by seismic methods. The variable tendency of the depth of high conductive asthenosphere receives a strong support from the heat flow measurements,Curie isothermic surface calculations and geochemical studies of the Cenozoic basalts. The strong shocks occurred there mainly along the margins of the uplift of the high conductive asthenosphere and the foci were located generally over the high conductive layer in the intermediate crust.