Earthquake swarms on transform faults
Earthquake swarms on transform faults
复制标题
转换断层上的地震群
DOI：
--
复制
发表时间：
2009
期刊：
影响因子：
--
通讯作者：
J. McGuire
中科院分区：
文献类型：
--
作者：
E. Roland;J. McGuire
摘要震群式地震序列通常在不同的地质环境中观察到，包括火山和地热区以及沿沿着转换板块边界。它们通常缺乏一个明确的主震，相对于其总的地震矩释放，覆盖了一个异常大的空间区域，并且根据标准的余震比例定律，它们不能及时衰减。岩群往往是由一个明显的驱动现象，如岩浆侵入，但大多数缺乏必要的地球物理数据来约束他们的驱动过程。要确定的机制，导致成群的走滑断层，我们使用相对的地震位置，以量化的空间和时间特征群沿着南加州和东太平洋隆起转换断层。这些区域的震群具有独特的特点，包括震源迁移速度范围相对较窄，大约为每小时1公里。这一速率对应于浅层蠕变瞬变的破裂传播速度，这种瞬变有时与震群一起在大地测量上观察到，并且明显快于通常与流体扩散相关的地震迁移速率。这里观察到的迁移率和低有效应力下降的均匀性表明，浅层地震蠕变瞬变是驱动走滑断层群的主要过程。此外，迁移率是一致的速率状态摩擦参数B（0.01）的实验室值，只要索尔顿海槽故障在静水条件下失败。
SUMMARY Swarm-like earthquake sequences are commonly observed in a diverse range of geological settings including volcanic and geothermal regions as well as along transform plate boundaries. They typically lack a clear mainshock, cover an unusually large spatial area relative to their total seismic moment release, and fail to decay in time according to standard aftershock scaling laws. Swarms often result from a clear driving phenomenon, such as a magma intrusion, but most lack the necessary geophysical data to constrain their driving process. To identify the mechanisms that cause swarms on strike-slip faults, we use relative earthquake locations to quantify the spatial and temporal characteristics of swarms along Southern California and East Pacific Rise transform faults. Swarms in these regions exhibit distinctive characteristics, including a relatively narrow range of hypocentral migration velocities, on the order of a kilometre per hour. This rate corresponds to the rupture propagation velocity of shallow creep transients that are sometimes observed geodetically in conjunction with swarms, and is significantly faster than the earthquake migration rates typically associated with fluid diffusion. The uniformity of migration rates and low effective stress drops observed here suggest that shallow aseismic creep transients are the primary process driving swarms on strike-slip faults. Moreover, the migration rates are consistent with laboratory values of the rate-state friction parameter b (0.01) as long as the Salton Trough faults fail under hydrostatic conditions.