Some Geodynamics Research Projects

The Initition of Subduction

One of the most important, unsolved problems in geophysics is the initiation of subduction. We know that new subduction zones must form because we see that subduction zones disapear in the geological record. Moreover, there are several well known subduction initiation events recorded in the Cenozoic history of the western Pacific. The geodynamics group has been actively studying subduction initiation and are involved with several on-going efforst to validate models and merge existing data sets with multi-scale geodynamic models.

Post Doctoral Scholar Chad Hall, working with Michael Gurnis and Luc Lavier, has recently discovered a mechanism for initiating an entirely new subduction zone, perhaps the most important unsolved problem in plate tectonics. Using a visco-elastoplastic model, they show that a fracture zone could be converted into a self-sustaining subduction zone after approximately 100 km of convergence. The entire system has a realistic rheology (non-linear, temperature-dependent, and visco-elastic). Modeled initiation is accompanied by rapid extension of the over-riding plate and explains the inferred catastrophic boninitic volcanism associated with Eocene initiation of the Izu-Bonin-Mariana (IBM) subduction zone. They estimate that the forces resisting IBM subduction initiation were substantially smaller than available driving forces at the time.

We then teamed up with Maria Sdolias and Dietmar Müller of Syndey University to show that the initiation of the IBM arc may have been preceeded by a change in the relative motion of the Pacific Plate with respect to Eurasia between 55 and 45 Ma. They were able to make their inference using global plate reconstructions.

Dynamics of the Meso-American Subduction zone

With other members of the Caltech Tectonics Observatory, we are developing multi-scale dynamic models of the Meso-American Subduction zone in support of MASE, the MesoAmerican Seismic Experiment. MASE is a deployment of 100 broadband seismomters for a period of 18 months over a 500 km transect perpendicular to the Middle American Trench. The TO team seeks to combine theory and observation into a dynamic model of the evolution of a subduction system over tens of millions of years, including the thermal and compositional state of the mantle wedge and melt production, the shape of the slab, coupling between the overriding and downgoing plates, thermal history of the upper plate, and forces operating on the entire system.

Post-Doctoral Scholar Vlad Manea is principally responsible for the development of these models. He is using the advanced software developed by the GeoFramework project, including CitcomS.py to formulate the time-dependent and instantaneous dynamics or this subduction zone.

Multi-Scale Models of Solid Earth Dynamics

Within the GeoFramework project, we have been developing a suite of tools to model multi-scale deformation for Earth science problems. This effort is motivated by the need to understand interactions between the long-term evolution of plate tectonics and shorter term processes such as the evolution of faults during and between earthquakes. The development of this tool is timely as it will form an integral component of new NSF initiatives, especially EarthScope and MARGINS, that will generate tremendous amounts of data, the interpretation of which will require a multi-scale modeling approach. The modeling suite handles complex rheologies, multiple scales in time and space, and is modular so users can add their own contributions. We are currently developing realistic three-dimensional models of subducted slabs, for example, using the CitComS.py finite element software. The FEM allows us to treat realistic lateral variations in viscosity, in addition radial variation. The image shown here shows the geoid over subducted slabs in the Western Pacific.