多地震活动性参数在断裂带现今活动习性与地震危险性评价中的应用与问题

THE APPLICATION AND LIMITATION OF MULTIPLE SEISMICITY PARAMETERS TO ASSESSING CURRENT FAULTING BEHAVIOR AND SEISMIC POTENTIAL OF ACTIVE FAULT ZONES

为了分析将地震活动性参数用于判定断裂带现今活动习性、进而评估长期地震危险性的可行性,文中介绍了沿断裂带进行b值扫描与填图的方法,以及进行断裂带分段的多参数值(—b、E、n和—a/—b)组合分析的资料处理、计算及分析步骤;提出了为进行多参数计算的、断裂带分段的参考判据,进而概括了根据计算的参数值、结合强震历史背景、现今地震分布综合分析断裂带现今活动习性空间差异的方法与思路。以5条地震活动水平和监测能力各异的断裂带为试验对象,基于归纳的方法综合分析了各断裂带现今活动习性的空间差异及潜在的地震危险段。文中还就断裂的震后调整运动与低b值的关系以及精定位的地震资料在参数计算中的合理使用等问题进行了讨论。主要认识为:以b值为主的若干地震活动性参数的空间分布可有效地用于断裂带现今活动习性及潜在强震危险段落的判定。沿断裂带b值扫描与填图以及断裂带分段多参数值组合分析两种方法,可分别应用于地震监测能力强和一般的地区;若在监测能力强的地区将两种方法结合起来使用,可获得更可靠的结果。晚期余震活跃或者大震后调整运动的断裂段也可表现出较低b或—b值的特点。

In order to analyze the feasibility using seismicity parameters to identify current faulting behavior and hence to assess long-term seismic potential of active fault zones, we introduced the technique of spatially scanning and mapping b values along fault zones, as well as the procedure of data processing, calculating and result analyzing of multiple-seismicity-parameter-value combinations（ i. e. b^-, n and a^-/b^-）for various fault-segments in this paper. We then brought forward several reference criteri- ons for fault segmentation, that is, the calculation of multiple seismicity parameters. Moreover, we generalized the approach and thinking of synthetically identifying spatial differences of current faulting behavior from the calculated parameters by combining histories of strong and major earthquakes and spatial distributions of modern seismicity. As an application, we took 5 active fault zones with various current seismicity levels and seismic detectabilities as the experimental targets to analyze synthetically the spatial differences of current faulting behaviors and identify fault segments with potential risk of strong earthquakes for each of the 5 fault zones basing on the generalized approach or methods. Meanwhile, the issues, such as the relation between the postseismic fault healing and relatively low b-value, the proper use of high-accurate re-located seismic data in the parameter calculating, and etc. have also been discussed. The results mainly suggest that the spatial distribution of multiple seismicity parameter values, among which the b-value is the most important one, can be effectively applied to analyzing current faulting behaviors and hence to identifying fault segments with potential risk of strong or major earthquakes. The two methods, the scanning and mapping of b-values along fault zones and the analysis of multi-parameter-value combinations for various fault-segments, can be applied to active fault zones in areas of high or moderate seismic detectability, respectively. And if the two methods are employed to areas with higher seismic detectability, more reliable results will be obtained. Fault-seg- ments with activity of late-stage aftershocks or with postseismic fault healing may have relatively low b or b-values too. We believe that once a catalog of earthquakes accurately relocated is used in calculation of seismicity parameters, it must contain the complete data of earthquakes occurring during the period and in the area studied, rather than only a part of data selected.