Aftershocks triggered by fluid intrusion: Evidence for the aftershock sequence occurred 2014 in West Bohemia/Vogtland
Aftershocks triggered by fluid intrusion: Evidence for the aftershock sequence occurred 2014 in West Bohemia/Vogtland
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DOI：
10.1002/2015jb012582
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发表时间：
2016-04
期刊：
影响因子：
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通讯作者：
S. Hainzl;T. Fischer;H. Čermáková;M. Bachura;J. Vlček
中科院分区：
文献类型：
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作者：
S. Hainzl;T. Fischer;H. Čermáková;M. Bachura;J. Vlček
位于欧洲中部的西波希米亚/沃格特兰地区以其重复的群体活动而闻名。然而，2014年的最新一次活动，尽管在空间上与之前的震群活动重叠，但由ML3.5、4.4和3.5事件触发的三个经典余震序列组成。根据震源机制和重新定位的地震资料，对ML4.4主震序列的细节进行了详细分析，破译了从震群型到主震余震的明显系统变化特征。分析表明，主震以旋转机制发生在断层面的阶跃区，不利于区域应力场的定向。其强烈的余震活动大多发生在平面内，具有如下经典特征：(1)余震的最大震级明显小于主震震级；(2)余震的衰减符合大森-宇津定律。然而，与典型序列相比，余震的绝对次数和拟合的大森-宇津c、p参数要大得多。通过流行性余震序列模型，我们发现一个强度呈指数衰减的附加无震源触发了很大一部分余震。相应的流体源流量呈指数下降的孔隙压力模拟结果与观测到的余震空间迁移前锋近似以log(T)形式扩展的结果吻合较好。因此，我们得出结论，主震打通了从有限流体源到断裂面的流体通道，解释了余震的异常高发生率、迁移模式和无震信号的指数下降。
The West Bohemia/Vogtland region, central Europe, is well known for its repeating swarm activity. However, the latest activity in 2014, although spatially overlapping with previous swarm activity, consisted of three classical aftershock sequences triggered by ML3.5, 4.4, and 3.5 events. To decode the apparent system change from swarm‐type to mainshock‐aftershock characteristics, we have analyzed the details of the major ML4.4 sequence based on focal mechanisms and relocated earthquake data. Our analysis shows that the mainshock occurred with rotated mechanism in a step over region of the fault plane, unfavorably oriented to the regional stress field. Most of its intense aftershock activity occurred in‐plane with classical characteristics such as (i) the maximum magnitude of the aftershocks is significantly less than the mainshock magnitude and (ii) the decay can be well fitted by the Omori‐Utsu law. However, the absolute number of aftershocks and the fitted Omori‐Utsu c and p parameters are much larger than for typical sequences. By means of the epidemic‐type aftershock sequence model, we show that an additional aseismic source with an exponentially decaying strength triggered a large fraction of the aftershocks. Corresponding pore pressure simulations with an exponentially decreasing flow rate of the fluid source show a good agreement with the observed spatial migration front of the aftershocks extending approximately with log(t) . Thus, we conclude that the mainshock opened fluid pathways from a finite fluid source into the fault plane explaining the unusual high rate of aftershocks, the migration patterns, and the exponential decrease of the aseismic signal.