Preslip and cascade processes initiating laboratory stick slip
Preslip and cascade processes initiating laboratory stick slip
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DOI：
10.1002/2014jb011220
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发表时间：
2014-08-01
影响因子：
3.9
通讯作者：
Lockner, David A.
中科院分区：
文献类型：
--
作者：
McLaskey, Gregory C.;Lockner, David A.
最近的模拟研究探索了地震是从大的非地震成核过程开始，还是从“级联”过程中较小不稳定性的快速增长动态开始。为了在实验室中探索这样的情况，我们研究了直径76 mm的圆柱形花岗岩实验室样品在40-120 Mpa围压下，光滑锯切断层的动态破裂(粘滑)的起始。我们使用高动态范围记录系统来直接比较粘滑事件期间辐射的地震波与微小(M-6)离散地震事件辐射的地震波，通常称为声发射(AEs)，发生在每次大粘滑之前的几秒钟内。AEs的地震矩、震源机制、位置和时间都有助于我们理解它们的机制，并为我们提供关于粘滑成核过程的信息。在10次粘滑的序列中，粘滑不稳定性记录的信号的前几微秒与前兆AEs的信号几乎无法区分。从这个意义上看，每次粘滑似乎都是作为一次声发射事件开始的，该事件在线性维度上迅速(类似于20亩S)增长约2个数量级，并破裂模拟断层的整个150 mm长。我们还测量了在粘滑前的最后几秒钟内加速的断层滑动。我们估计，这种滑动至少有98%是无地震的，它既削弱了断层，又产生了AEs，最终将级联起来，启动更大的动态破裂。
Recent modeling studies have explored whether earthquakes begin with a large aseismic nucleation process or initiate dynamically from the rapid growth of a smaller instability in a "cascade-up" process. To explore such a case in the laboratory, we study the initiation of dynamic rupture (stick slip) of a smooth saw-cut fault in a 76 mm diameter cylindrical granite laboratory sample at 40-120 MPa confining pressure. We use a high dynamic range recording system to directly compare the seismic waves radiated during the stick-slip event to those radiated from tiny (M - 6) discrete seismic events, commonly known as acoustic emissions (AEs), that occur in the seconds prior to each large stick slip. The seismic moments, focal mechanisms, locations, and timing of the AEs all contribute to our understanding of their mechanics and provide us with information about the stick-slip nucleation process. In a sequence of 10 stick slips, the first few microseconds of the signals recorded from stick-slip instabilities are nearly indistinguishable from those of premonitory AEs. In this sense, it appears that each stick slip begins as an AE event that rapidly (similar to 20 mu s) grows about 2 orders of magnitude in linear dimension and ruptures the entire 150 mm length of the simulated fault. We also measure accelerating fault slip in the final seconds before stick slip. We estimate that this slip is at least 98% aseismic and that it both weakens the fault and produces AEs that will eventually cascade-up to initiate the larger dynamic rupture.