1976年唐山7.8级地震成因探讨

Discussion on the Genesis of the 1976 Tangshan M7.8 Earthquake

根据唐山地区莫霍面隆升、大地构造、新构造运动特征,探讨1976年唐山7.8级地震发生的地质构造背景。唐山地震区位于辽翼台向斜北部,北邻燕山台褶带,地表发育规模不大的基岩断裂,为燕山期活动形成,新生代断裂活动性不强;地下发育深切地幔的深大断裂,与地表断裂位置相当。由震前地震前兆及震后异常现象,提出了地震发生的成因机制。唐山地震是由震前地幔拱起、岩浆上涌垂直力作用下,受NEE-SWW向区域应力场水平挤压,NNE-NE向唐山右旋剪切逆断裂活动,受阻于NW向蓟运河左旋剪切正断裂,地壳岩石间摩擦、破裂,两断裂在深部共轭交汇区应力闭锁、释放,最终导致该次地震的孕育、发生。

According to the characteristics of Moho uplift, tectonics and neotectonic movement in Tangshan area, the geological tectonic background of Tangshan M7.8 earthquake in 1976 is discussed.Tangshan earthquake area is located in the north of Liaoyitan syncline, adjacent to the Yanshantai fold belt in the north.The small-scale bedrock faults developed on the surface are formed by Yanshanian activities, and the Cenozoic faults are not very active.There are deep and large faults in the deep mantle, which are similar to the surface faults.Based on the precursors of earthquakes and the abnormal phenomena after earthquakes, the genesis mechanism of earthquakes is proposed.The Tangshan Earthquake was caused by the vertical force of mantle arch and magma upwelling before the earthquake. Under the horizontal compression of NEE-SWW trending regional stress field, the NNE-NE trending Tangshan dextral shear reverse fracture activity was hindered by the NW trending left-lateral shear normal fracture of Jiyunhe, the friction and fracture between crustal rocks, and the stress locking and release of the two faults in the deep conjugate junction area. It eventually led to the gestation and occurrence of the earthquake.