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通过对1976年7月28日唐山大震前后地壳形变资料的分析,探讨了唐山地区现今构造活动特征和应力作用方式。结果表明,区内现今构造活动主要是沿袭新华夏构造体系的构造形迹而进行,但活动方式和力学性质有所改变。大震前后的形变资料一致表明,隆起和凹陷的长轴方向,以及活动最明显的断裂均以北北东向占优势。北北东向断裂的活动方式以顺时针扭动并兼有垂直升降为特征。震区及邻区的断层微量位移和短水准等测量结果也表明.北北东——北东向断裂多表现为压顺扭,北西向显张性兼反扭,近东西向断裂呈张性。实测断裂活动方式,大震构造裂缝带的特征及摸拟实验结果均表明本区构造应力场的主压应力方向为近东西向。唐山大震的发生,就是北北东向活动断裂带的发展受到北部强大的阴山东西构造带的阻挡形成相对的“闭锁”区,在近东西向压应力作用下,逐渐积累应变能,孕育成为大的震源体,直至地应力超过岩石的抵抗强度而突破“闭锁”,产生地震。
Based on the analysis of crustal deformation data before and after the Tangshan earthquake on July 28, 1976, the characteristics of tectonic activities and the mode of stress action in Tangshan area are discussed. The results show that the tectonic activities in the area are mainly followed the tectonic features of the Neo-Huaxia tectonic system, but the activity modes and mechanical properties have been changed. The deformation data before and after the earthquake show consistently that the major axes of the uplift and depression and the faults with the most obvious activities are dominated by north-north eastward. The north-east-trending faults are characterized by clockwise twists and vertical movements. Measurements of fault microseismic displacements and short leveling in the quake zone and its adjacent areas also show that the North-EAST-NEWR is mostly characterized by compression and torsion, dilatation and anti-twist in the NW direction, and tension in the NE / W direction. The results show that the principal compressive stress direction of the tectonic stress field in this area is near east-west. The occurrence of the Tangshan earthquake is that the north-north eastward active fault zone is blocked by the strong Yinshan structural zone in the north to form a relatively “locked-up” zone. Under the action of near-EW compressive stress, strain energy gradually accumulates and becomes Large source body, until the stress exceeds the rock’s resistance to break the “lock”, resulting in earthquakes.