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本文从应力场角度分析了1976年唐山地震发生的可能力源。震前唐山地区除受有太平洋板块和印度板块的作用外,主要受有附近的热力源的作用。以渤中为中心的下辽河—渤中—黄骅上地幔隆起的高温区和沧东断裂水平温度梯度带的存在,使唐山地区位于热应力集中区。本文根据已有的观测结果,提出了将温度变化区简化为圆形、狭长矩形和椭圆形等三个力学模式,分别求得它们的解析解,并计算了它们的热应力场。结果表明:在增温区以内,正应力都是压应力,剪应力很小。在增温区以外,法向应力为压应力,周向应力为张应力,水平剪应力较大,但各个应力分量随着距离增加而衰减,只在增温区的边缘地带达到最大值,其数值有几百巴的数量级。唐山恰好位于该增温区的边缘地带,表明热力源是促使唐山地震发生的重要原因。 除唐山地震外,华北地区近年发生的几个大地震如邢台、河间、渤海、海城地震,以及1983年发生的菏泽地震,均位于热应力的高值地带,这些地震的孕育和发生显然也与热力源的作用有关。
This paper analyzes the possible sources of the Tangshan earthquake in 1976 from the stress field. Before the earthquake, the Tangshan area was mainly affected by nearby heat sources except for the role of the Pacific plate and the Indian plate. The existence of the high temperature zone of the lower Liaohe-Bozhong-Huanghua upper mantle uplift and the horizontal temperature gradient of Cangdong fault centered on Bozhong makes the Tangshan area located in the thermal stress concentration area. In this paper, based on the existing observations, three mechanical models are proposed, which simplify the temperature change region into a circle, an elongated rectangle and an ellipse, respectively, and obtain their analytical solutions and calculate their thermal stress fields. The results show that within the temperature increase zone, the normal stress is compressive stress and the shear stress is small. Outside the temperature increase zone, the normal stress is compressive stress, the circumferential stress is tensile stress and the horizontal shear stress is larger, but the stress components decay with the increase of distance and reach the maximum only in the edge of the warming area. The numerical value is on the order of hundreds of bar. Tangshan is located in the edge of the warming area, indicating that the heat source is an important reason for the Tangshan earthquake. In addition to the Tangshan earthquake, several major earthquakes in recent years in North China, such as Xingtai, Hejian, Bohai and Haicheng earthquakes, and the Heze earthquake in 1983 are all located in the high thermal stress region. The occurrence and occurrence of these earthquakes are obvious Also related to the role of heat source.