A survey of 71 earthquake bursts across southern California: Exploring the role of pore fluid pressure fluctuations and aseismic slip as drivers
A survey of 71 earthquake bursts across southern California: Exploring the role of pore fluid pressure fluctuations and aseismic slip as drivers
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DOI：
10.1029/2005jb004034
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发表时间：
2005-12
影响因子：
--
通讯作者：
J. Vidale;P. Shearer
中科院分区：
文献类型：
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作者：
J. Vidale;P. Shearer
[1] 我们通过检查 1984 年至 2002 年间南加州的波形重定位目录，并系统地识别 2 公里半径范围内、间隔 4 周内发生的 40 次或更多地震的 71 个孤立序列，来调查地震爆发的原因。 71 次爆发中的 57 次很难解释为主要是主震及其符合大森律的前震和余震，因为它们在空间、时间和震级上表现出更复杂的演变；我们确定其中 18 个序列特别像群体。反对简单级联弹性应力触发的证据包括稳定地震活动率区间的存在、最大事件在序列中较晚发生的趋势、某些群与其累积矩相比的较大空间范围，以及每次爆发中的事件数量与每次爆发中最大事件的震级之间的弱相关性。浅层层序和正常断层机制层序最有可能呈群状。群状序列中震源出现在垂直面上并随时间扩展的趋势表明，孔隙流体压力波动是驱动群状地震活动爆发的最可能机制。然而，阵发性地震滑移也可能至少是部分原因，并且可能为地震群期间地震活动的稳定速率提供更有说服力的解释，而流体压力扰动可能会随着时间的推移而更快地减少。余震类和群状地震活动爆发都分布在整个研究区，表明它们是构造断层的普遍特征，而不是局限于火山或地热区等少数地质条件。
[1] We investigate the cause of seismicity bursts by examining a waveform-relocated catalog for southern California between 1984 and 2002 and systematically identifying 71 isolated sequences of 40 or more earthquakes occurring within a 2-km-radius volume and a 4-week interval. Fifty-seven of the 71 bursts are difficult to interpret as primarily a main shock and its Omori-law-abiding foreshocks and aftershocks because they exhibit a more complicated evolution in space, time, and magnitude; we identify 18 of these sequences as particularly swarm-like. Evidence against a simple cascade of elastic stress triggering includes the presence of an interval of steady seismicity rate, the tendency of the largest event to strike later in the sequence, the large spatial extent of some of the swarms compared to their cumulative moment, and the weak correlation between the number of events in each burst and the magnitude of the largest event in each burst. Shallow sequences and normal faulting mechanism sequences are most likely to be swarm-like. The tendencies of the hypocenters in the swarm-like sequences to occur on vertical planes and expand over time suggest pore fluid pressure fluctuations as the most likely mechanism driving the swarm-like seismicity bursts. However, episodic aseismic slip could also be at least partly responsible and might provide a more compelling explanation for the steady rate of seismicity during swarms, whereas fluid pressure perturbations might be expected to diminish more rapidly with time. Both aftershock-like and swarm-like seismicity bursts are distributed across the entire study region, indicating that they are a general feature of tectonic faulting, rather than limited to a few geological conditions such as volcanic or geothermal areas.