陈学忠^1,,
李艳娥¹,
陈丽娟²
1. 中国地震局地球物理研究所, 北京 100081
2. 重庆市地震局, 重庆 401147

基金项目: 国家重点研发计划（2018YFC1503405）资助


详细信息

作者简介: 陈学忠, 男, 1963年生, 研究员, 主要从事地震学研究.E-mail: cxz8675@163.com

中图分类号: P315

收稿日期:2020-12-05
修回日期:2021-06-22
上线日期:2021-10-10

Anomalies of the b value prior to the M_S7.8 Tangshan Earthquake of 1976

CHEN XueZhong^1,,
LI YanE¹,
CHEN LiJuan²
1. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
2. Chongqing Earthquake Adminitration, Chongqing 401147, China


MSC: P315

--> Received Date: 05 December 2020
Revised Date: 22 June 2021
Available Online: 10 October 2021


摘要
摘要:基于应力与b值之间的负相关关系，b值一直是地震预测研究和地震危险性分析的内容之一.在b值分析时，一个是特定时段的空间扫描分析，另一个是选定空间范围内的时间进程分析.b值的空间分布可以反映各个地区b值的差异性，但难以将其与地震孕育相联系.同样，在进行b值随时间变化分析时，难以保证所选取的区域完全包含b值异常区.有震例研究表明，地震发生前b值存在数月-数年的下降变化过程.本文中，我们着眼于b值下降变化过程，通过格点搜索法，分析1976年唐山M_S7.8地震前b值异常特征.结果表明：b值下降异常大面积集中分布在京—津—唐一带地区，在这个异常区内唐山M_S7.8地震发生前b值大约从1973年6月到1974年10月经历了17个月的下降过程，从1.1降至0.72，相对下降幅度约为35%.在之后的20个月中，b值一直维持在低值，没有明显变化.在b值处于低值期间，从1975年4月—1976年6月，b值异常区的应变释放是加速的.
关键词: 唐山地震/
b值/
异常特征/
格点搜索

Abstract:The b value in the frequency-magnitude relation is commonly used in the analysis of seismic hazards based on its inverse relationship with stress. When analyzing the b value, spatial scanning is performed for a specific period, or the change in the b value over time is analyzed for a selected region. The spatial distribution of the b value shows how the value differs from place to place. But it is difficult to associate such spatial differences of the b value with the occurrence of major earthquakes. Similarly, when analyzing the variation in the b value over time for a selected region, it is difficult to ensure that the area of abnormal b values lies completely within the selected region. Case studies have shown that for some earthquakes, the b value exhibits a decreasing tendency from several months to several years before earthquake occurrence. In this article, we focus on temporal changes of the b value and adopted the lattice searching for analyzing anomalies in the b value prior to the 1976 M_S7.8 Tangshan earthquake. The results show that, in this case, the abnormal drop of the b value was concentrated in the Beijing-Tianjin-Tangshan area, and the b value decreased from 1.1 to 0.72—a relative fall of 35%—within this area during the 17-month period from June 1973 to October 1974. In the subsequent 20 months prior to the earthquake, the b value remained low without substantial changes. The strain release within the area of the b value anomaly accelerated from April 1975 to June 1976, during which the b-value was still low.
Key words:Tangshan earthquake/
b value/
Anomalies/
Lattice searching



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