华南沿海地区地震环境特征的定量研究及其在地震区划中的应用

QUANTIFICATION OF SEISMOGENIC ENVIRONMENT IN SOUTH CHINA COASTAL AREAS AND ITS APPLICATION TO SEISMIC ZONATION

以华南沿海地区为研究区 ,将Bayes公式应用于地震环境特征与地震事件的相关性定量化研究中 ,在GIS技术的支持下 ,由统计某一因素不同类型所占的面积及发生在其上的中强地震数 ,得到地震发生的后验概率。为评价地质及地球物理各因素与地震关系的相对重要性 ,引入了系统工程学中的层次分析方法 ,最终得到研究区内以累积概率为指标的地震综合危险图 。

It is known that strong earthquakes are usually associated with regional active tectonics and certain geophysical anomalies reflecting the features of regional deep structures. In this paper, the Bayes formula in statistic is used to quantify the relationship between the earthquake and the factors of seismogenic environment. These factors include active fault, Quaternary basin, Bouguer anomaly and geomagnetic anomaly. As a measure of the relationship between the earthquake and the factors, the posterior probability of each type can be calculated as:P(C j|E)=P(E|C j)P(C j)∑mi=1P(E|C i)P(C i) The meaning of this equation is that when a strong earthquake E occurs, the probability of this event to occur on type j is P(C j|E) In this paper, south China coastal areas are selected as the testing area. The active faults in this area are classified into 10 groups according to their strikes with an interval of 18°, while the geophysical anomaly zones are classified into 5 grades. The results show that among the 10 groups of active faults, the NE to NEE-trending (0°～53°) and NW-trending (306°～323°) faults bear a close relationship with strong earthquakes. Geologic and geophysical factors are of different importance to strong earthquakes. The Analytic Hierarchy Process (AHP) is applied to determine this relative importance. The following factors are selected to set up the judgment matrix for the studied area: Active fault ( B 1), Quanternary basin ( B 2), Bouguer anomaly ( B 3) and Geomagnetic anomaly ( B 4). [BHDWG10mm,WK20mm,K10mm,WK10mm?3W]Strong earthquake B 1B 2B 3B 4B 11577B 21/5155B 31/71/511B 41/71/511 The eigenvector of the maximum eigenvalue ( λ max =8.971 4) for the pairwise comparison matrix is W=〔0.557 3,0.312 1,0.065 3,0.065 3〕, which is the weights of the relative importance of the different factors. The range of the studied area is 110°～118°E,19°～26°N, which is divided into 5 600 small square grids with a size of 0.1° in longitude and latitude. With the help of GIS, the cumulative probability of each square grid is obtained. Based on the quantitative analysis of regional seismogenic environment in South China costal areas, two major seismic belts are outlined. Among them, the inner seismic belt has a lower value of seismic risk than the outer belt.