Publications

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2006
Elkhoury, JE, Brodsky EE, Agnew DC.  2006.  Seismic waves increase permeability. Nature. 441:1135-1138.   10.1038/nature04798   AbstractWebsite

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).

1991
Agnew, D.  1991.  How complete is the pre-instrumental record of earthquakes in southern California? Environmental perils, San Diego Region. ( Abbott PL, Elliott WJ, Eds.).:75-88., [San Diego, Calif.]: Published for the Geological Society of America Annual Meeting by the San Diego Association of Geologists Abstract
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Agnew, DC, Ellsworth WL.  1991.  Earthquake Prediction and Long-Term Hazard Assessment. Reviews of Geophysics. 29:877-889. AbstractWebsite
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1979
Legg, M, Agnew D.  1979.  The 1862 earthquake in San Diego. Earthquake and Other perils: San Diego region. ( Abbott PL, Elliott WJ, Eds.).:139-141., San Diego: San Diego Association of Geologists Abstract
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Agnew, D. C; Legg, SM; C.  1979.  Earthquake history of San Diego. Earthquake and Other perils: San Diego region. ( Abbott PL, Elliott WJ, Eds.).:123-138., San Diego: San Diego Association of Geologists Abstract
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Agnew, D.  1979.  Tsunami history of San Diego. Earthquake and Other perils: San Diego region. ( Abbott PL, Elliott WJ, Eds.).:117-122., San Diego: San Diego Association of Geologists Abstract
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