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Seismic waves increase permeability


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 earthquakes1,2,3,4,5,6,7. Distant earthquakes may even increase the permeability in faults8. Most of these hydrological observations can be explained by some form of permeability increase1,5. 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° in the phase of the water level response to the dilatational volumetric strain of the semidiurnal tidal components of wells at the Piñon Flat Observatory in Southern California. After the earthquakes, the phase gradually returns to the background value at a rate of less than 0.1° 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 properties9. 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 faults10.

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Figure 1: Water level from wells CIB and CIC.
Figure 2: Map of Southern California, showing epicentres of earthquakes considered in this study, as selected by the criterion in Fig. 1.
Figure 3: Phase of the semidiurnal tide for the water level in the wells CIB and CIC, relative to the areal strain.
Figure 4: Change in permeability for the well–aquifer systems CIB (circles) and CIC (squares) at the time of each of the earthquakes, plotted against peak ground velocity measured at PFO.


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These measurements would not have been available without the long-term support of the PFO by the NSF, SCEC, the Vetlesen fund of the Scripps Institution, and the US Geological Survey; and the efforts of F. Wyatt, L. Weuve, S. Bralla, and S. Docktor. We gratefully acknowledge comments and discussion from E. Cochran, P. Davis, Z. Peng, A. Sagy and J. Vidale. J.E.E. was supported by a CIED scholarship and an NSF award.

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Correspondence to Jean E. Elkhoury.

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Elkhoury, J., Brodsky, E. & Agnew, D. Seismic waves increase permeability. Nature 441, 1135–1138 (2006).

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