关于唐山地震前震中区地应力测值张性跳动的原因

On the Mechanism of Observed Tensile Pulsations of Ground Stress Before Tangshan Earthquake

唐山地震前,地震主断裂附近的陡河站和赵各庄站都观测到垂直于该断裂方向的地应力张性跳动,根据地震前跨该断裂的水准观测数据,认为这是地壳沿该断裂的局部凸起使地表附近沿该方向出现张性裂隙的反映。在其扩展的过程中,测量元件与张裂隙前沿的相对位置将发生变化。通过对张裂隙前沿附近应力场的分析,不仅可以说明当裂隙前沿在元件附近经过时与裂隙垂直的元件测值为什么突然上升后又下降恢复到原来的水平,而且可以说明另外两个与该元件呈60°交角的元件的同时刻测值变化不大的原因。

Tensile pulsations of stress normal to the Tangshan fault had been observed at Douhe and Zhao-gezhuang stations prior to the Tangshan earthquake. Based on the pre-earthquake levelling across the fault, it is considered in correspondence with the local crustal swelling along the fault which may have produced tensile fractures parallel to it in the rocks near the surface. When the front of such a fracture advances downwards, its position relative to the probe changes. Analysis of the stress fields adjacent to the front provides explanations to not only the tensile pulsations in the stress normal to the fault but also the rather smooth changes in those at an angle of 30° to th fault.