Collaborative Research: Multi-scale models of subduction zone earthquake cycle observations

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Earth's tectonic plates get recycled back into the mantle at subduction zones. The largest earthquakes happen there, and these megathrust environments also generate a range of other geohazards including tsunamis and volcanoes, making their study of great societal relevance. Recently, seismological and geodetic measurements have revealed a range of phenomena associated with megathrust behavior that are not captured by a simple, stick-slip earthquake cycle model of slow loading and catastrophic rupture. These newly discovered phenomena include transient, creeping events of fault slip on decadal scales which may indicate preparatory behavior of the fault system, perhaps systematically linked to the main seismic event. Mechanical models have not quite kept up with these new discoveries and our understanding of the physical processes behind these phenomena is incomplete. A new, integrative framework is therefore needed to understand the physical mechanisms and fault constitutive laws behind complex deformation and seismicity patterns. This project seeks to develop such a mechanical model, initially for the data rich Japan setting, in order to understand regional megathrust dynamics and fault interaction patterns, as well as improve seismic hazard estimates. Later, such a mechanical model may potentially be deployed at other subduction zones such as Cascadia and assist in interpreting existing and planned monitoring data streams for earthquake forecasting and early warning. To capture the spatial and temporal scales involved in this complex problem, three sub-projects are to be pursued in collaboration between researchers at University of Texas Austin (UTIG), Purdue University, and the University of Tokyo: 1) The development of sets of multi earthquake-cycle scenarios based on numerical models of visco-elastic, inter-, pre-, co- and post-seismic fault loading in Japan. 2) The development of global mantle flow and regional, time-evolving mantle convection models to understand long-term, subduction induced forcing of plate boundaries and backarcs in the region. 3) The development of cross-timescale, visco-elasto-plastic models in 3-D, incorporating rate and state friction as well as other fault constitutive laws in a dynamically consistent, thermo-mechanical convection framework. This will enable, for example, studying the role of pre-seismic, slow slip phenomena for fault zone evolution, eventually in the presence of fluid flow. All project parts will be integrated, and results from different approaches cross-checked. Moreover, all sub-projects are complementary and will guide the establishment of the general subduction zone model that is needed to understand earthquake cycle observations and seismicity in Japan and elsewhere.