川西地震重点监视防御区的近期地震趋势及分段发震概率

RECENT EARTHQUAKE TREND AND SEGMENTED PROBABILITIES OF EARTHQUAKE OCCURRENCE IN THE KEY REGON OF EARTHQUAKE MONITORING AND DEFENDING IN WESTERN SICHUAN

川西地震重点监视防御区的确定,首先基于本世纪第五强震活跃幕川滇地区强震活动空间分布图象的结构性转移;二是该区“第一类地震空区”或“空段”的存在及强地震复发周期接近;三是大地形变复测证实监视区内“闭锁段”和“隆起区”的存在;四是在其空段和闭锁段或隆起区近年曾发生注目的中等地震活动;五是测震和其它微观前兆趋势性异常出现,说明所圈定监视区的中期强震危险性存在。本文通过构造活动速率、历史地震计算的复发概率值和测震学及微观前兆异常信度的分析和综合信度运算,探讨并给出了川西地震重点监视区及附近地区的近期分段发震概率。

The key region of earthquake monitoring and defending in western Sichuan are determined on the basis of evidences as follows. First, there occurred structural transfer on the spatial distribution pattern of strong earthquakes in Sichan—Yunnan area during the fifth active episode of strong earthquake in this century; Second, there exists the first type of 'gap'or'gap segment'in this region, and the recurfence period of strong earthquake has been approaching; Third, it is confirmed by the repeated survey of geodetic deformation that there exist'blocked segment'and'uplift area'in the region; Fourth, there occurred spectacular moderate seismicity in these'gap segmet', 'blocked segment'or'uplift area'; Fifth, there appeared trend anomalies of seismometry results and other microscopic precursors, implying that middle—term risk of strong earthquake exists in the determined monitoring region. This paper presents and discusses recent segmented probabilities of earthquake occurrence in the key region of earthquake monitoring in western Sichuan. Based on the calculation of recurrence probabilities from the rates of tectonic movements and the data of historic earthquake, the analyses of confidence levels for seismometry results and microscopic precursor anomalies, and the calculation of integrated confidence level.