景谷6.6级、鲁甸6.5级地震序列应力降变化对比研究

Comparative study of changes in stress drop of the Jinggu MS6.6 and Ludian MS6.5 earthquake sequences

摘要:

利用云南2014年10月7日景谷6.6级、8月3日鲁甸6.5级地震序列的波形与震相资料，消除区域地震波衰减与台站场地响应后，计算得到2次地震序列的应力降。结果显示，在研究所涉及的震级范围内，应力降呈现随震级增大而增大的趋势。为尽可能消除震级对应力降的影响，对比了相同震级档地震的应力降，结果显示，景谷地震序列的平均应力降明显高于鲁甸地震，这可能与2次6.5级左右地震后震源区的应力状态有关。从序列余震应力降的时、空变化对比来看，景谷6.6级地震后至2014年12月6日5.8、5.9级强余震发生前，应力降变化呈现先缓慢下降、进而转折升高并持续高值的变化过程；同时，高应力降地震在空间上主要集中于5.8级强余震区域。这表明，主震发生后经过一个较短期的调整之后，5.8级强余震震源区的应力环境可能持续增强。5.8、5.9级强余震发生后，地震序列应力降快速下降至相对稳定状态。研究表明，2次6级左右强余震发生后，震源附近区域应力得到一定程度的释放，应力环境降低，地震序列活动也趋于结束。对于后续没有强余震发生的鲁甸地震序列，余震应力降小于景谷地震序列相同震级档地震的平均应力降，同时，主震后余震序列的应力降在时间上几乎未发生太大的变化；结合主震能量释放特点推测，震源区的应力在主震破裂过程中已得到较多的释放，主震后震源区应力变化呈现逐渐恢复的过程，这可能是鲁甸地震余震活动明显较弱，后续亦未有较强余震发生的原因之一。

Abstract:

The earthquake stress drops of the Jinggu M_S6.6 and Ludian M_S6.5 earthquake sequences in Yunnan are calculated on the basis of waveform data and seismic phase data after eliminating the effects of regional seismic wave attenuations and station site responses. The results show that the stress drop increases with magnitudes within the scope of this study. After eliminating the influence of the magnitude,the average value of stress drop in the Jinggu earthquake sequence is higher than that of the Ludian earthquake sequence at the same magnitude range. This may be related to the stress state in different regions. In terms of the changes of time and space of stress drop,before the M_S5.8 strong aftershock,the stress drop shows a process of “slow down-turning up-maintain high value” after the mainshock. Meanwhile,almost all the high stress drop earthquakes are distributed around the M_S5.8 strong aftershock. It shows that stress environment in the region is increasing after the mainshock. And after the M_S5.9 strong aftershock,stress drop rapidly declines to a relatively stable state. After the two earthquakes,the regional tectonic stress releases more fully,and its stress environment begins to reduce rapidly:For the Ludian earthquake sequence without subsequent strong aftershocks,the average value of stress drop is lower than the Jinggu earthquake sequence at the same magnitude range. At the same time,the stress drop of aftershock sequences almost does not change too much in time after the mainchock. Combining with the releasing characteristics of the main energy,the stress in the region is excessively released,and the subsequent stress in the region gradually returns to normal. This may be the reason why the activity of the Ludian aftershock is significantly weaker and there is no subsequent strong aftershock.