Source Mechanisms of Induced Earthquakes at The Geysers Geothermal Reservoir
Source Mechanisms of Induced Earthquakes at The Geysers Geothermal Reservoir
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DOI：
10.1007/s00024-014-0795-x
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发表时间：
2014-08-01
影响因子：
2
通讯作者：
Johnson, Lane R.
中科院分区：
文献类型：
--
作者：
Johnson, Lane R.
在加利福尼亚州北部的间歇泉地热水库，有证据有力地表明，与电力生产相关的活动导致了小地震数量的增加。作为西北间歇泉控制实验的一部分，一阶动态矩张量被用来研究诱发地震与井内注水之间的关系。间歇泉复杂浅部地壳的动态矩张量的估计具有挑战性，因此对该方法进行了详细的描述，并特别注意了结果的不确定性。对于矩震级为0.9-2.8的地震事件，在1-100赫兹的频率范围内可以可靠地恢复动态矩张量的谱模，但相关谱相的不确定性使它们的应用仅限于几个简单的结果。研究了几种不同的静力矩张量，其中首选的静力矩张量是从与动态力矩张量的谱系数相匹配的模型参数中获得的。一组20次地震的估计矩张量显示了一系列震源机制，其中超过一半的地震具有显著的各向同性正号或负号部分。弯矩张量各向同性部分的角频率比偏矩张量的平均值大约40%。震源机制存在一些空间模式，空间上密切相关的地震往往具有相似的机制，但同时，附近的一些地震具有非常不同的机制。震源区的位移张力轴主要是水平的，而压力轴的范围从近水平到垂直。向研究区域中心的井中注入水显然会增加每天的地震次数，但对震源机制的影响并不明显。
At The Geysers geothermal reservoir in northern California, evidence strongly suggests that activities associated with production of electric power cause an increase in the number of small earthquakes. First-degree dynamic moment tensors are used to investigate the relationship between induced earthquakes and injection of water into a well as part of a controlled experiment in the northwest Geysers. The estimation of dynamic moment tensors in the complex shallow crust at The Geysers is challenging, so the method is described in detail with particular attention given to the uncertainty in the results. For seismic events in the moment magnitude range of 0.9-2.8, spectral moduli of dynamic moment tensors are reliably recovered in the frequency range of 1-100 Hz, but uncertainty in the associated spectral phases limits their use to a few simple results. A number of different static moment tensors are investigated, with the preferred one obtained from parameters of a model fitted to the spectral modulus of the dynamic moment tensor. Moment tensors estimated for a group of 20 earthquakes exhibit a range of source mechanisms, with over half having significant isotropic parts of either positive or negative sign. Corner frequencies of the isotropic part of the moment tensor are about 40 % larger than the average of the deviatoric moment tensor. Some spatial patterns are present in source mechanisms, with earthquakes closely related in space tending to have similar mechanisms, but at the same time, some nearby earthquakes have very different mechanisms. Tensional axes of displacement in the source regions are primarily horizontal, while the pressure axes range from near horizontal to vertical. Injection of water into the well in the center of the study area clearly causes an increase in the number of earthquakes per day, but an effect upon source mechanisms is not evident.