台网监测能力变化及其对地震活动性研究的影响

The Influence of Detection Changes of Network on Seismicity Research

地震目录是研究地震活动性的基本资料。然而地震目录的内容不仅反映了地震活动性的真实变化,也混杂了人为因素引起的变化。这些人为因素包括,台网监测能力的增强或减弱,台网测定震级的系统偏差等。本文首先讨论了对地震频度和平均震级进行z检验以研究地震活动性和识别人为变化的方法,继而对京津唐张地区的资料进行z检验。计算结果表明,北京台网的监测能力在1966年和1984年后曾经有过两次提高,这与北京遥测台网网志的报告大体一致。计算结果也反映出当前台网在震级确定上还存在一些系统偏差,文中讨论了这些偏差对客观地研究地震活动性和地震预报的影响,指出了排除人为因素对地震活动性研究的重要意义。

Earthquake catalogs provide basic data set for the study of seismicity. However,they often contain man-made changes in addition to real activity. The man-made changes include variations in detection of networks,magnitude shifts in magnitude estimates,etc. In order to identify man-made changes in seismicity study,a method of z test on average magnitude and seismicity rate is described. This method is applied to the Beijing-Tianjing-Tangshan-Zhangjiakou area in China. The results show two major detection increases of the Beijing local network in 1966 and 1984 respectively. The study also indicates that systematic magnitude shifts exist in magnitude estimates in the Beijing seismic network. The effect of such magnitude shifts on seismicity and earthquake prediction is significant and elimination of man-made changes is necessary in seismicity research.