青藏块体中北部中强地震前弱震活动统计特征研究

Study on Statistical Features about Weak Earthquake Activity before Moderate-strong Earthquakes Occurred in Middle Northern Part of the Qinghai-Tibet Block

对于青藏块体中北部1970～2003年间震前弱震记录情况较好的5级以上地震,通过4个基本不相关的参数———地震时间集中度参数Ct、地震空间集中度参数Cd、η值和弱震频次等刻画震前地震的时空集中分布特征以及地震活动的增强与异常平静。通过对计算结果的分析研究,得到青藏块体中北部5级以上地震前,弱震活动的频次往往会出现升高或降低,强度也往往会出现明显增强,并经常会伴随着随时、空集中分布的现象。

For earthquakes with M ≥ 5.0 occurred in middle northern part of the Qinghai-Tibet Block from 1970 ～ 1973 before which weak earthquakes were recorded well, through 4 parameters which are basically not correlated——earthquake time centralization degree parameter C1 value, earthquake space centralization degree parameter Cd value, η value and weak earthquke frequency to describe the time, space centralization distribution features of weak earthquakes and the strength and anomalous quiescence of seismic activity before main shocks. It has been obtained that before earthquakes with M ≥ 5.0 occurred in middle northern part of the Qinghai-Tibet Block, the frequency of weak earthquakes otten shows ascent and drop. The strength often shows obvious enhancement and the centralization distribution as time and space is often accompanying.