Source parameters and rupture velocity of small M ≤ 2.1 reservoir induced earthquakes
Source parameters and rupture velocity of small M ≤ 2.1 reservoir induced earthquakes
复制标题
M≤2.1级小水库诱发地震的震源参数和破裂速度
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
A. Nascimento
中科院分区：
文献类型：
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作者：
J. Tomić;R. Abercrombie;A. Nascimento
总结
本文计算了ML≤ 2.1的浅源水库诱发地震的应力降和破裂速度，发现它们与天然大地震的应力降和破裂速度相似。以往的研究表明，水力压裂、采矿和采矿诱发的地震比天然构造地震具有更低的平均应力降。这种差异可能是由于构造背景不同或诱发地震震源深度较浅所致。另外，在早期的研究中，在校正衰减和场地效应方面的困难可能会导致低估应力降。此外，大多数研究假设小型水库诱发地震的破裂速度与大地震的破裂速度相同。我们分析了巴西东北部Acu水库水位变化引起的101次ML≤ 2.1级地震。这些地震都是浅层地震（深度<5公里），该地区的自然地震活动可以忽略不计。我们用三种不同的方法计算了六个最大地震（1.9 ≤ML≤ 2.1）的震源参数。我们对各个光谱进行建模，以找到拐角频率、与频率无关的Q和长周期振幅。我们用共点小震作为经验绿色函数来计算谱比，并确定相对震源时间函数。源持续时间和拐角频率的估计意味着应力下降的范围为26-179 MPa。这些地震与构造地震相似或高于构造地震，表明震源深度较浅和水的存在不会影响应力降。我们观察到其中一次地震有明显的方向性，并利用脉冲宽度的方位角变化估计破裂速度≥0.6β。
SUMMARY
We calculate stress drop and rupture speed for ML≤ 2.1 shallow reservoir induced earthquakes and find them to be similar to those of large, natural earthquakes. Previous studies have suggested that hydrofractures, mining and reservoir-induced earthquakes have lower average stress drop than natural tectonic earthquakes. This difference might result from the different tectonic setting or the shallower hypocentral depths of induced earthquakes. Alternatively, difficulties in correcting for attenuation and site effects in earlier studies may lead to underestimation of stress drop. In addition, most studies assume the rupture velocity of small reservoir induced earthquakes to be the same as for the large earthquakes. We analyse a set of 101 ML≤ 2.1 earthquakes induced by changing water level in the Acu Reservoir, NE Brazil. The earthquakes are shallow, (depth <5 km) and the region has negligible natural seismicity. We use three different approaches to calculate the source parameters of the six largest (1.9 ≤ML≤ 2.1) earthquakes. We model the individual spectra to find corner frequency, frequency-independent Q, and long period amplitude. We use collocated small earthquakes as empirical Green's functions to calculate the spectral ratios, and determine the relative source time functions. Estimates of the source duration and corner frequency imply stress drops in the range of 26–179 MPa. These are similar to, or higher than tectonic earthquakes suggesting that the shallow hypocentral depth and the presence of water do not affect stress drop. We observe clear directivity for one of the earthquakes, and use the azimuthal variation in pulse width to estimate a rupture velocity of ≥0.6β.