2014年鲁甸M_S6.5地震前后地震活动性

Temporal evolution of seismicity before and after the 2014 Ludian M_S6.5 earthquake

2014年8月3日在云南省鲁甸县发生M_s6.5地震,造成了巨大的人员伤亡和财产损失.关于鲁甸地震的起因,特别是鲁甸地震与溪洛渡水库之间的关系存在一些争议.分析中强地震前后地震活动性的变化可以为判断主震起源提供一定的依据.然而,由于鲁甸地震震中附近固定台站数目少、台站距离震中远及主震后尾波干扰等因素的影响,会造成地震目录的缺失,从而可能影响地震活动性的可靠分析.为了获得更加完备的地震目录,本文采用模板匹配方法对鲁甸地震前后小地震进行了搜索和识别.以台网目录中的541个事件作为模板,在主震之前33天到主震后5天的连续波形中识别出991个未在目录中列出的地震,使余震的完备震级从1.8降低到1.3.根据检测目录得到主震前33天内的&值为1.04±0.18,余震的b值在震后5天内由0.5左右逐渐上升至0.9附近并保持稳定;根据2009年到主震发生前的台网目录得到该区域的背景b值为0.93±0.04.即鲁甸地震前后区域地震活动b值均与背景b值接近,这与典型水库诱发的中强震具有的b值特征不相符.同时通过进一步分析台网目录,未发现溪洛渡水库蓄水前后研究区域内的地震活动性存在明显变化,这也与典型水库诱发地震区域的地震活动性特征不相符.综合以上结果,我们认为2014年鲁甸M_s6.5地震不具有典型水库诱发地震的特征.

The MS6.5 Ludian earthquake occurred on 3 Aug 2014 in Yunnan province, which caused massive human casualties and property losses. After the earthquake, the cause of this earthquake has been a controversial issue, especially its relation with the Xiluodu reservoir. Analysis of seismicity before and after the earthquake can provide some evidence for answering this question. But some small earthquakes may be missing in the network catalog due to small number and sparse distribution of seismic stations, and overlapping between small earthquakes and coda waves of the large earthquake, which may influence the analysis of seismicity. In this article, we adopt a matched filter technique to detect missing events in the period 33 days before and 5 days after the Ludian earthquake and obtain 991 missing events by using 541 events listed in the network catalog as templates, decreasing the Mc of aftershock from 1.8 to 1.3.From the detected catalog, we estimate the b values within 33 days before and 5 days after the main shock. The results show that the b value within 33 days before the main shock is 1.04±0.18, within 5 days it increases from 0.5 to 0.9 and remains stable, while the background b value is 0.93±0.04 from the network catalog 5 years before the main shock. The character of the b value doesn＇t match the variation of that associated with well accepted reservoir-induced earthquakes. We also find that the seismicity is almost the same before and after impoundment of the Xiluodu reservoir in this region by analyzing the network catalog of 5 years before the main shock. Based on these observations, we suggest that the 2014 Ludian MS6.5 earthquake does not bear the characters of typical reservoir-induced earthquakes.