华北地区强震活动特点研究

Research on Activity Characteristics of Strong Earthquakes in North China

华北地区是我国的政治、经济和文化中心,也是我国地震多发地区之一。华北地区历史地震资料记载时间较早且较为连续,是研究我国强震活动的理想试验场。选取第三、第四活动期M≥6.0地震目录作为基础资料研究华北地区强震活动特点。首先探讨华北地区强震活动与活动地块、边界带的关系,然后从时间和空间上分析华北地区强震活动的轮回性阶段及其期幕活动特点,最后计算未来5年华北地区发生下一次M≥6.0地震的累积概率和条件概率。研究结果表明:①华北地区M≥6.0地震活动主要集中在活动地块的边界带,M≥7.0地震则全部发生在活动地块的边界带上,同时华北地区地震应变释放速率与边界带的构造活动速率呈线性相关;②第四活动期各活跃幕的能量释放均低于第三活动期,因此华北地区未来仍可能发生M≥6.0地震;③第三、第四活动期的主体活动区存在显著差异,且第四活动期的强震活动较第三活动期向东迁移;④在2020年年初发生第四活动期闭幕M≥6.0地震的累积概率为80%左右,而在2022年年底前发生M≥6.0地震的条件概率为50%。本研究可为华北地区地震大形势分析和中长期地震危险性预测提供重要参考。

North China is the most central area for politics,economy and culture of our country,and also one of the earthquake-prone areas in China.The historical record for seismic data in North China is earlier and more continuous,and it is an ideal site for strong earthquake activity studying.This paper has selected the M≥6.0 earthquake catalogue in the third and fourth active periods as the basic data to study the activity characteristics of strong earthquakes in North China.Firstly,the relations of strong earthquake activity levels to active-tectonic blocks and boundaries in North China are discussed.Then,the recurrent phase and episodic characteristics of strong earthquake activities from time and space in North China are analyzed.Finally,the cumulative and conditional probabilities of the M≥6.0 earthquakes in North China are calculated to evaluate earthquake occurrence in this region after five years.The results suggest①the M≥6.0 earthquakes are mainly concentrated in active-tectonic boundaries,the M≥7.0 earthquakes all happened in active-tectonic boundaries,and the linear relation between seismic strain-releasing rates and tectonic deformation velocities of active-tectonic boundaries in North China;②Because energy releases of activity curtains in the fourth seismic active periods are lower than that of the third seismic active periods,it seems that M≥6.0 earthquakes will occur in North China in the future;③There are obviously different major regions of strong earthquakes between the third and fourth seismic active periods in North China,earthquake activities of the fourth seismic period migrate eastward compared with the third seismic period;④If the current quiet episode of the M≥6.0 earthquakes ends in the beginning of 2020,the accumulated seismic probability of the M≥6.0 earthquakes is about 80%;and if the current quiet episode of the M≥6.0 earthquakes ends by the end of 2022,the conditional seismic probability is 50%.This study can provide significant reference for the analysis of overall seismic trend and medium-to-long term earthquake hazard prediction in North China.