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A mechanism for sustained groundwater pressure changes induced by distant earthquakes

E. E. Brodsky·E. Roeloffs·D. Woodcock·I. Gall·M. Manga
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Abstract

Large sustained well water level changes (>10 cm) in response to distant (more than hundreds of kilometers) earthquakes have proven enigmatic for over 30 years. Here we use high sampling rates at a well near Grants Pass, Oregon, to perform the first simultaneous analysis of both the dynamic response of water level and sustained changes, or steps. We observe a factor of 40 increase in the ratio of water level amplitude to seismic wave ground velocity during a sudden coseismic step. On the basis of this observation we propose a new model for coseismic pore pressure steps in which a temporary barrier deposited by groundwater flow is entrained and removed by the more rapid flow induced by the seismic waves. In hydrothermal areas, this mechanism could lead to 4 ?? 10-2 MPa pressure changes and triggered seismicity.

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Journal of Geophysical Research B: Solid EarthArticle

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E. E. Brodsky, E. Roeloffs, D. Woodcock, I. Gall, M. Manga. 2003. A mechanism for sustained groundwater pressure changes induced by distant earthquakes. https://pubs.usgs.gov/publication/70025130

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