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本文分两个部分研究了我国西部滇、川、甘地区一些强震发生前周围地区中强地震和小地震的活动特征。 首先研究了强震前周围地区中强地震围空区的一般形态、围空区形成时间与强震震级的关系、形成地震围空区各阶段的持续时间以及地震围空区特征与地质背景条件的关系。 其次还研究了近年来川、滇地区一些强震发生前震区及其周围地区3级以上小地震的活动特征。并从强震前震区及其周围地区小地震的空间分布图象,小地震的频度和强度随时间变化的特征以及有无直接前震等方面探讨了发生在“块间”地区和“块内”地区强震的不同特点。发现发生在“块间”地区的强震,震前小震活动性很低,形成“空区”,多无直接前震。而发生在“块内”地区的强震,震前小震活动性高,形成“条带”状分布,震前从几秒到几个月内有3.0—5.5级的直接前震活动。发生在“块间”地区和“块内”地区的强震前小震活动具有的这种不同的特征可能与发震地区的构造、结构条件、应力状态以及边界条件有关。
This paper studies the characteristics of moderate-strong earthquakes and small earthquakes in the surrounding areas before the occurrence of some strong earthquakes in the western Yunnan, Sichuan and Gansu regions in two parts. Firstly, the general morphology of the mid-strong earthquakes in the surrounding area before the strong earthquakes, the relationship between the formation time of the air space and the magnitude of the strong earthquakes, the durations of the various stages of the formation of the seabed and the characteristics of the geo-environment and the geological background conditions Relationship. Secondly, we also study the activity features of some earthquakes above Grade 3 before and after the occurrence of some strong earthquakes in Sichuan and Yunnan in recent years. In this paper, the spatial distribution of small earthquakes in the area before and after the strong earthquakes and the features of the intensity of the small earthquakes with time and whether or not the earthquakes are directly discussed are discussed. “Different Features of Regional Strong Earthquakes. The strong earthquakes that occurred in the ”inter-block“ region were found. The activity of small earthquakes before earthquakes was very low, forming a ”vacant zone“ with no direct foreshock. The strong earthquakes that occurred in the ”intrablock“ region had high activity of small earthquakes before the earthquake, forming a ”ribbon“ -like distribution. There were 3.0-3.5 direct foreshock events within a few seconds to a few months before the earthquake. The different characteristics of the small earthquakes that occurred before the strong earthquakes in the ”inter-block“ and ”intra-block" areas may be related to the tectonics, structural conditions, stress states and boundary conditions in the seismogenic area.