唐山大震前后震区构造应力场的光弹性模拟实验

本文根据唐山震区的地质构造模拟制作光弹模型,以N60°E方向加压进行唐山震前应力场的光弹性模拟实验。用打孔的方法模拟强震的应力释放。实验结果表明:1.在N60°E方向压缩时,唐山—丰南一带、滦县、野鸡坨和卢龙等地区是最大剪应力集中区,与唐山7.8级、滦县7.1级地震及强余震的震中分布基本吻合。说明唐山大震及余震的发生是近东西向压应力场作用的结果。2.当唐山7.8级地震应力释放后,震前具有高应力背景值的其它地区,应力进一步加强。说明唐山地震的发生导致了应力场的重新调整,增强了强余震发震的动力条件。3.实验结果证明,在断裂带两侧、端部或几条断裂的复合部位,其主应力方向与区域应力场的总体方向比较,大致有10°～25°的偏转。强震的应力释放导致震中区附近的主应力方向与震前相比也发生约10°～20°的偏差。

A PHOTOELASTIC EXPERIMENT FOR SIMULATING TECTONIC STRESS FIELD IN SEISMIC REGION BEFORE AND AFTER TANGSHAN EARTHQUAKE

The purpose of this paper is to outline a photoelastic experiment with a model for the tectonic stress field of the Tangshan region under a compression in N60°E direction. In the same experiment, the stress release of the strong earthquake was also simulated by using the method of hole-drilling. The results are as follows:1. When the Tangshan region was undergoing a compression in N60°E direction, the maximum shear stress was concentrated at the Tangshan-Fengnan district, Yejituo village, Luanxian county and Lulong county. These stress concentration regions were mostly corresponding to the epicentral areas of the Tangshan earthquake(M=7.8), the Luanxian earthquake(M=7.1) and their strong aftershocks. It has been recognized that the occurrences of the Tangshan earthquake and its aftershocks were due to the compressive stress field in nearly EW direction.2. Though the stress was released during the Tangshan earthquake (M=7.8), it still increased in those areas when the background value of stress was high before the earthquake event. This shows that a readjustment of the stress field was caused by the Tangshan earthquake, thus intensifying the dynamical conditions for the occurrences of the strong after-shocks.