Subduction zones are home to two of the most spectacular and dangerous natural hazards on Earth: megathrust earthquakes and tsunamis. To mitigate risk, we must better understand the earthquake cycle in subduction zones: What fraction of relative plate motion is accommodated aseismically instead of seismically, and to what extent do estimates of the seismic coupling coefficient allow one to predict the extent of future megathrust earthquakes? What role does inelastic deformation of the accretionary prism play in rupture dynamics? What determines the up-dip extent of slip, a key factor controlling the seafloor uplift and tsunami height? And what causes the slow rupture process of tsunami earthquakes that produce vastly larger tsunamis than expected from the amplitude of seismic waves at periods less than ~10 s? These questions will be addressed with three-dimensional numerical simulations capable of resolving interseismic loading, creep and slow slip, and fully dynamic spontaneous ruptures, with realistic geometries and heterogeneous material structure. The solid Earth component of the model will be fully coupled to a compressible ocean, in order to simultaneously capture seismic waves, hydroacoustic (ocean sound) waves, and surface gravity waves (tsunamis). Attention will be placed on the hydroacoustic signature of subduction earthquakes, as recorded by ocean bottom pressure sensors. Hydroacoustic waves excited by seafloor displacement arrive at the coast many minutes before the tsunami, and could potentially be used to estimate tsunami wave heights for use in early warning systems. Simulations will be conducted for the 2011 Tohoku-Oki earthquake and other recent events, and comparisons made to seismic, geodetic, tsunami, and ocean acoustic data.
The largest earthquakes on Earth occur in subduction zones along the boundary between tectonic plates, such as the Cascadia subduction zone offshore Washington and Oregon. These earthquakes cause vertical uplift of the seafloor, generating tsunamis. This project is aimed at characterizing hazards from these earthquakes and tsunamis using computational simulations coupling the response of the solid Earth, including frictional sliding along faults, and the ocean. The simulations will capture the earthquake rupture process, as well as excitation and propagation of seismic waves, hydroacoustic waves (sound waves in the ocean), and tsunamis. Specific models will be developed for the 2011 Tohoku-Oki, Japan, earthquake and other recent events, and comparison made to a range of geophysical data to validate the modeling approach. Preliminary simulations of the Tohoku-Oki earthquake suggest that hydroacoustic waves, which can be recorded by cabled ocean bottom pressure sensors deployed tens or a hundred kilometers offshore, might be used to rapidly estimate tsunami wave heights for use in an early warning system. This research effort will be complemented with an outreach education program aimed an increasing awareness of and preparedness for natural hazards in the Central Coast region of California, through a partnership between Stanford and Allan Hancock College (AHC), a Hispanic-serving community college in the Central Coast. The PI will work with faculty and students at AHC to develop earthquake and tsunami demonstrations and activities for use in AHC?s Friday Night Science outreach programs attended by 600?1000 members of the community. Each summer, the PI will host an AHC student in an eight-week research internship at Stanford.
