Constraining Frictional and Low-Temperature Plastic Rheology of Oceanic Lithosphere by Modeling Observations of Load-Induced Deformation from the Hawaiian Islands to Japan Trench

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

Plate tectonics is arguably the most important physical process of the solid Earth. From the fundamental science point of view, plate tectonics controls the thermal evolution of the Earth by recycling the relatively cold and stiff surface layer (i.e., the crust and lithosphere) to the hot interiors of the Earth's mantle to cause its cooling down with time, which determines the generation of Earth's magnetic field. Plate tectonics is a unique feature to the Earth and does not exist for other terrestrial planets in our solar system. Plate tectonics is suggested to play an important role in regulating the Earth's climate system. Plate tectonics also carves the most important surface topographic features such as ocean basins, mid-ocean ridge systems, and major mountain belts. Plate tectonics dictates that deformation occurs primarily at plate boundaries (i.e., where different plates meet) through earthquakes with volcanism as by-products. However, the cause of plate tectonics remains largely unknown, despite decades of research. This project is aimed at uncovering the physical mechanism for plate tectonics. The key aspect of this project is to formulate state of art physical and dynamic models to integrate the observed deformation caused by earthquakes, topography and gravity anomalies into our understanding of plate tectonics generation. This project will support a PhD student and includes significant international collaboration. The further development a community finite element code for modeling viscoelastic, non-linear deformation of lithosphere and mantle, will be made available to the community through NSF-supported CIG (Computational Infrastructure for Geodynamics). This project seeks to model observations of earthquake deformation, topography and gravity anomalies to constrain lithospheric rheology in both plate interior (i.e., Hawaii) and convergent plate boundary (Japan trench or subduction zone) settings. The project addresses the following three geophysical questions. First, what constraints would the observations of load-induced lithospheric deformation at the Japan trench and Hawaii place on the low-temperature plasticity flow laws and coefficient of friction in these two different tectonic settings? Second, how does lithospheric rheology in the Japan trench compare with that at Hawaii? Considering that the Japan trench is downstream of Hawaii along the Pacific plate motion, does the lithospheric rheology evolve from Hawaii to Japan trench and how? Third, how do the low-temperature plasticity flow laws constrained by the observations at Japan trench and Hawaii compare with those derived from laboratory studies including recent experiments? To answer these questions, this project will carry out the following specific tasks: 1) Estimate seismic strain rate for the Hawaiian region and Japan trench from earthquake information, quantify their uncertainties, and compile other observations including lithospheric deflection near Hawaii and at Japan trench and outer rise and free-air gravity; 2) Formulate loading models for the Japan trench and Hawaii to compute the observables of lithospheric strain rate, topography and gravity for different low-temperature plasticity flow laws and coefficient of friction, and compare them with observations to place constraints on the rheology; 3) Test low-temperature plasticity flow laws from recent experiments, examine the effect of the activation energy and different lithospheric thermal structure on load-induced lithospheric deformation, and re-calibrate the lithospheric yield strength. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.