Seismic waves increase permeability
Seismic waves increase permeability
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DOI：
10.1038/nature04798
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发表时间：
2006-06-28
期刊：
影响因子：
64.8
通讯作者：
Agnew, Duncan C.
中科院分区：
文献类型：
--
作者：
Elkhoury, Jean E.;Brodsky, Emily E.;Agnew, Duncan C.
据观察，地震会以各种方式影响水文系统--地震时，水井水位会发生显著变化，溪流会变得更满，泉水流量会增加（1-7）。远距离地震甚至可能增加断层的渗透性（8）。大多数水文观测结果可以用某种形式的渗透性增加来解释（1，5）。在这里，我们使用水井水位固体地球潮汐的响应，以测量渗透率超过20年的时间。在每一个在南加州的七次地震的时间，我们观察到瞬态变化高达24度的水位响应的相位的半日潮汐分量的威尔斯在Pinon平天文台在南加州的体积应变。地震后，相位以每天小于0.1度的速度逐渐恢复到背景值。我们使用一个轴对称流模型，该模型由通过单一、横向延伸、封闭、均质和各向同性含水层的外加水头振荡驱动，以将相位响应与含水层特性联系起来（9）。我们将相位响应的变化解释为由于渗透率的变化。在地震发生时，该地点的渗透性增加了三倍。在0.21-2.1 cm·s ~（-1）范围内，渗透率的增加与地震波峰值速度的幅值近似成线性关系。这种渗透率的增加是水文学家和油藏工程师感兴趣的，因为它们影响流体流动，并可能决定水文和含油系统的长期演变。地震学家也可能对它们感兴趣，因为由此产生的孔隙压力变化可以通过改变断层上的正应力来影响地震（10）。
Earthquakes have been observed to affect hydrological systems in a variety of ways-water well levels can change dramatically, streams can become fuller and spring discharges can increase at the time of earthquakes(1-7). Distant earthquakes may even increase the permeability in faults(8). Most of these hydrological observations can be explained by some form of permeability increase(1,5). Here we use the response of water well levels to solid Earth tides to measure permeability over a 20-year period. At the time of each of seven earthquakes in Southern California, we observe transient changes of up to 24 degrees in the phase of the water level response to the dilatational volumetric strain of the semidiurnal tidal components of wells at the Pinon Flat Observatory in Southern California. After the earthquakes, the phase gradually returns to the background value at a rate of less than 0.1 degrees per day. We use a model of axisymmetric flow driven by an imposed head oscillation through a single, laterally extensive, confined, homogeneous and isotropic aquifer to relate the phase response to aquifer properties(9). We interpret the changes in phase response as due to changes in permeability. At the time of the earthquakes, the permeability at the site increases by a factor as high as three. The permeability increase depends roughly linearly on the amplitude of seismic-wave peak ground velocity in the range of 0.21-2.1 cm s(-1). Such permeability increases are of interest to hydrologists and oil reservoir engineers as they affect fluid flow and might determine long-term evolution of hydrological and oil-bearing systems. They may also be interesting to seismologists, as the resulting pore pressure changes can affect earthquakes by changing normal stresses on faults(10).