RAPID: Hydrological responses to the August, 2014, Napa earthquake

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Earthquakes generate hydrological responses, such as increases in stream flow and changes in the water level in wells. Such hydrologic responses are important because they provide unique insight into the coupling of hydrologic and tectonic processes at spatial and temporal scales that are otherwise difficult to study. The August 2014 magnitude 6 Napa earthquake caused several previously dry stream to begin flowing, an unexpected source of water during a time of intense drought. The study of earthquake-induced hydrologic changes has implications for water resources and engineering, including assessing the role of earthquakes in damaging aquifers, affecting underground repositories, and changing water supplies. The origin of hydrologic responses to earthquakes has been the subject of controversy, in large part because there are many models to explain observations and few measurements suitable for distinguishing between hypotheses. The Napa earthquake provides a unique opportunity to test hypotheses because water emerged in dry or nearly dry streams and hence was not diluted by water already flowing at the surface. The PI will collect water samples and make discharge measurements over a 1-year period in order to answer the following questions: a) Does the excess discharge in streams originate from the shallow or deep subsurface? b) Are there permanent changes in properties of the subsurface such as permeability? c) Are static or dynamic stresses more important for explaining the observed changes?