Speaker: Harold Tobin, UW Department of Geology and Geophysics
Abstract: Understanding of the processes by which earthquakes occur remains one of the great challenges of geophysics. The complex interplay among frictional processes, stress, pore fluid pressure, temperature, and other factors means that a comprehensive model for fault physics has not been achieved. One reason for this is the lack of in situ observations and samples from within the faults deep beneath the earth's surface. To address this problem, several major projects have been launched to drill into fault zones. The massive subduction earthquakes which occur at the boundary between two tectonic plates at subduction zones are especially of interest because they cause devastating tsunami, and occur with repeating characteristics. Off the Pacific coast of Japan, the NanTroSEIZE (Nankai Trough Seismogenic Zone Experiment) project targets a subduction zone for drilling to sample and place instruments into and around the fault zone responsible for these tsunami-generating earthquakes. Three-dimensional seismic reflection surveys image the plate boundary zone and provide evidence for fault properties. Drilling provides evidence on the rock composition, chemistry, stress, and other parameters. These unique new datasets are helping to test theoretical and laboratory-derived models for fault physics. I will discuss the overall challenge and present results from the first phase of drilling in 2007-2008.