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1976年7月28日北京时间03时42分56秒河北省唐山市区(东经118°11′;北纬39°38′)发生7.8级地震,震中烈度达十一度。当日18时45分37秒于附近的滦县商家林(东经118°39′;北纬39°50′)又发生7.1级地震,震中烈度达九度。本文简述唐山地震参数的测定及其发震的地质背景,并对大震前本区较大范围内地震活动的某些异常特征,如围空区、密集—平静、b值下降及条带状的空间分布等进行了一些讨论。根据大震时的地面断裂走向、P波初动图解、大震前后的垂直形变以及余震位置分布等资料推测,7.8级地震可能是北东走向的断层以走滑为主的右旋滑动结果。7.1级地震可能是近南北走向的滦河断层受北东向断层牵动发生的水平左旋运动。文中还从唐山余震时空分布特点出发,讨论了震源的破裂过程及其对余震发展的影响。并指出唐山大震的发生时间可能与当天的天文条件有关。
July 28, 1976 Beijing Time 3:42:56 An earthquake measuring 7.8 on the Richter Scale has hit Earthquakes of 11 degrees in the urban area of Tangshan, Hebei Province (118 ° 11’E; latitude 39 ° 38’N). At 7.15am on the same day, a 7.1-magnitude earthquake hit Luanxian Shanglin (longitude 118 ° 39’E; latitude 39 ° 50’E) nearby and the intensity of the epicenter reached nine degrees. This paper briefly describes the determination of Tangshan earthquake parameters and the geological background of the seismogenic events. It also analyzes some anomalous features of seismic activity over a large area before the earthquake, such as enclave, dense-calm, declining b value and banding Like the spatial distribution of a number of discussions. The magnitude 7.8 earthquake may be the result of the right-lateral slip with strike-slip as the main strike of the 7.8-magnitude earthquake, based on the data of the first strike of the P wave, the vertical deformation before and after the earthquake, and the distribution of aftershocks. The 7.1-magnitude earthquake may be a horizontal left-lateral movement of the Luanhe fault that is near-north-northbound due to the northeast fault. Based on the temporal and spatial distribution of aftershocks in Tangshan, the paper also discusses the rupture process of the source and its impact on the development of aftershocks. And pointed out that the occurrence time of Tangshan earthquake may be related to the astronomical conditions of the day.