Contained Laboratory Earthquakes Ranging From Slow to Fast
Contained Laboratory Earthquakes Ranging From Slow to Fast
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DOI：
10.1029/2019jb017865
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发表时间：
2019-10
期刊：
影响因子：
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通讯作者：
Bill S. Wu;G. Mclaskey
中科院分区：
文献类型：
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作者：
Bill S. Wu;G. Mclaskey
加载包含锯切模拟断层的3 m花岗岩板，我们产生了在到达样品末端之前自发成核、传播和停止的滑动事件。这项工作表明，慢（0.07毫米/秒的滑动速度）和快速（100毫米/秒）包含滑动事件可以发生在同一故障补丁。同时给出了辐射地震波在时域和频域上的系统性变化。慢地震持续时间为100毫秒，并辐射叠加在其地面运动低频分量上的类似震颤的信号。它们通常在缓慢滑动（蠕变）之前发生，并且它们的地震辐射具有ω−1的频谱形状，类似于自然界中观察到的慢地震。最快的地震的滑动速度、应力降和视应力（分别为0.2 m/s、0.4 MPa和1.2 kPa）与典型的M −2.5级地震相似，具有单一明显的角频率和高频处的ω−2谱衰减，与布伦震源模型很好地拟合。慢速和快速之间的差距被中间事件填充，源谱在拐角频率附近耗尽。这项工作表明，一个故障补丁的长度为p的条件下，有利于破裂可以辐射在极大地不同的方式，在ph* 的基础上，其中h* 是一个关键的成核长度尺度的微小变化。这种机制可以帮助解释在构成构造震颤的低频地震中观察到的非典型尺度。
Loading a 3‐m granite slab containing a saw‐cut simulated fault, we generated slip events that spontaneously nucleate, propagate, and arrest before reaching the ends of the sample. This work shows that slow (0.07 mm/s slip speeds) and fast (100 mm/s) contained slip events can occur on the same fault patch. We also present the systematic changes in radiated seismic waves both in time and frequency domain. The slow earthquakes are 100 ms in duration and radiate tremor‐like signals superposed onto a low‐frequency component of their ground motion. They are often preceded by slow slip (creep) and their seismic radiation has an ω−1 spectral shape, similar to slow earthquakes observed in nature. The fastest events have slip velocity, stress drop, and apparent stress (0.2 m/s, 0.4 MPa, and 1.2 kPa, respectively) similar to those of typical M −2.5 earthquakes, with a single distinct corner frequency and ω−2 spectral falloff at high frequencies, well fit by the Brune earthquake source model. The gap between slow and fast is filled with intermediate events with source spectra depleted near the corner frequency. This work shows that a fault patch of length p with conditions favorable to rupture can radiate in vastly different ways, based on small changes in ph*, where h* is a critical nucleation length scale. Such a mechanism can help explain atypical scaling observed for low‐frequency earthquakes that compose tectonic tremor.