Hydrologic responses to earthquakes, such as increases in steam flow or changes in the water level in wells, are not uncommon. 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 origin of hydrologic responses to earthquakes has been the subject of controversy, in large part because there are many models to explain observations and almost no measurements suitable for distinguishing between hypotheses. On October 30, 2007 a magnitude 5.6 earthquake occurred near the Alum Rock springs, California. The PI monitoring these springs for the past 5 years in order to provide a benchmark for post-seismic changes in discharge and water composition. Over the first 5 days following the earthquake he documented a three-fold increase in discharge. The Alum Rock springs discharge along one strand of the Hayward fault. They discharge water that is a mixture of local meteoric water and connate waters expelled from depth.
The PI will use stable isotope analyses of water samples collected over a 3 month time period following the earthquake in order to test proposed models for the origin of the increased discharge. Because the spring water at each spring is geochemically distinct it should be possible to document changes in fault zone plumbing. It will also be possible to determine whether the source of the excess water flowing from the springs originates at depth, or in the shallow subsurface.
This project offers an interdisciplinary opportunity to understand fault zone structure and evolution. In particular it will provide new (and probably unique) constraints on the role of fluids in fault zone processes. The PI will integrate the monitoring of the springs with courses taught at UC Berkeley, including freshman seminars, undergraduate-level geodynamics, and graduate level classes. The results will also be communicated with the managers of Alum Rock Park where the springs are located. The park is a popular destination for local residents and K-12 student field trips. The springs are the main draw of the park and this work can be used to update interpretative signs and displays.
