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本文根据西南地震台网15年以上的地震连续资料,研究了1965至1979年川滇地区发生的9次强震(M_s≥6.7)震前区域中等地震(M_L≥4.0)活动性时、空演变特点。结果表明:(1)主震前2至4年内,在震中周围200—300公里范围内,中等地震活动的频度和强度,在正常活动背景上有一个明显的加强过程,持续时间为1至3年,增加的最大值不仅偏离多年平均值而且达3σ以上。(2)异常地震在空间活动上,具有条带性,围空性和收缩性等多形式的分布特点;(3)震前出现平静期。震前地震活动性异常图象与强震孕育过程有关,反映了区域应力场应力变化过程。震前中等地震活动的集中区,正是其后强震发生的地区;异常图象在其主震后随即消失;异常地震空间分布与主震震源机制解有关;异常地震活动在出现和转折时间上与震前多种前兆异常变化相一致。
Based on the continuous seismic data of Southwest Seismostation for more than 15 years, this paper studies the spatial evolution of moderate earthquakes (M_L≥4.0) during the nine strong earthquakes (M_s≥6.7) occurred in Sichuan-Yunnan region from 1965 to 1979. Features. The results show that: (1) Within 2 to 4 years before the main shock, the frequency and intensity of moderate earthquakes within the range of 200-300 km around the epicenter have an obvious strengthening process on the normal activity background with a duration of 1 to Three years, the maximum increase not only deviate from the multi-year average and up to 3σ above. (2) The anomaly earthquakes have the spatial distribution of banding, encirclement and contractility in space activities; (3) The quiescence occurs before the earthquake. The anomalous seismic activity anomalies before the earthquake are related to the process of strong earthquakes and reflect the process of stress changes in the regional stress field. The focus area of moderate seismic activity before the earthquake is the area where the strong earthquakes occurred; the anomalous image disappears immediately after the main shock; the spatial distribution of anomalous earthquakes is related to the focal mechanism solution of the main shock; the occurrence of anomalous earthquakes at the occurrence and transition time On the earthquake with a variety of precursory abnormal changes consistent.