Speaker: Dr. Marine Denolle; Assistant Professor of Earth and Planetary Sciences at Harvard University
Being at the interface between the solid Earth and the fluid Earth, the shallow subsurface is particularly affected by the evolution in atmospheric conditions (temperature, pressure, precipitations) and by the transient effects of seismic activity. Because we live at this interface and rely on the surface properties for food, water, and energy resources, we ought to understand its response to changes in environmental and seismic factors. The mechanical properties of the subsurface affect the speed and attenuation of seismic waves passing through the medium. We use the ambient seismic field to extract information on the variations in seismic wavespeeds. First, we monitor ground water resources by predicting fluctuations in ground water storage in the San Gabriel Valley aquifer (California) and by predicting water table levels in fractured rocks aquifer in Medford (Massachusetts). Second, we measure long term temporal changes in seismic velocities in Kanto sedimentary basin (Japan) due to atmospheric conditions and to damage due to strong ground motions, which highlight the complex rheology of unconsolidated sediments.