Integrating Marine Seismic and Ocean Drilling Results with three-dimensional dynamic models of Subduction Initiation

This project seeks to better understand a process called subduction. Subduction is where cold oceanic plates return to Earth’s interior. Plate subduction is a key geological process responsible for the largest forces on tectonic plates, the site of the most destructive earthquakes on the planet and leads to much of the volcanism on Earth’s surface.

The project will look at the process of forming a new subduction zone, which is called subduction initiation. Subduction initiation is poorly understood but is associated with the largest changes in the forces which both drive and resist plate tectonic motions. Although many aspects of plate tectonics are understood, subduction initiation remains a key unknown and there has been a concerted effort in the last few years to understand this process through marine geological and geophysical research.

This project will synthesize the recent marine research with what are called plate tectonic reconstructions and incorporate that information into computational models. Some of the key evidence that constrains the process has come from deep sea drilling and through marine seismic surveys. These data constrain the details of the geological evolution and present-day structure of the sites of subduction initiation, respectively.

The project will focus on four sites of recent or on-going subduction initiation: Izu-Bonin Mariana south of Japan, Tonga Kermadec in the southwest Pacific, Puysegur south of New Zealand and Matthews-Hunter near Fiji also in the southwest Pacific. It has recently been discovered through ocean drilling that the Izu-Bonin-Mariana and the Tonga-Kermadec subduction zones may have initiated at the same time despite being separated by several thousand miles and were associated with a major change in the motion of the Pacific Plate.

This project will look at the details of how these subduction zones formed in terms of the basic physics of solid and fluid mechanics. During subduction initiation, the so-called mega thrust fault, the site of destructive great earthquakes, forms. It is thought that such a new megathrust is in the process of forming south of New Zealand.

In this project sophisticated computational methods, call finite elements, will be used and will use the largest supercomputers supported by the National Science Foundation. During the project, a graduate student will be trained in computational methods, which are widely applicable to many areas of science and engineering. The investigator will work with the Caltech Seismo Lab Outreach and Social Media office to communicate science to the broad, diverse community of the Los Angeles community, including through visits to local public schools.

The initiation of new subduction zones is a key component of plate tectonics but remains an unsolved problem. With subducted slabs being the primary force driving plate motions, formation of new subduction zones and demise of existing ones are associated with the largest changes in the forces on tectonic plates. There was an ocean basin-wide tectonic change in the Pacific at about 50 Ma with initiation of IBM and Tonga-Kermadec synchronous with a change in plate motions.

This project will squarely address these fundamental problems by exploiting the recently expanded observational record from deep sea drilling and marine seismic surveys. The team of geoscientists will test concepts for the initiation of subduction by comparing observations against a new generation of 3D, time-dependent geodynamic models. With the observational constraints on subduction initiation through ocean drilling and marine seismic surveys jumping forward over the last six years simultaneous with a commensurate maturing of software and computational hardware, the time is ideal to readdress the mechanics of subduction initiation.

The investigators will build detailed regional plate tectonic reconstructions (data models) for four western Pacific subduction initiation events: Izu-Bonin Mariana (IBM), Tonga Kermadec, Puysegur and Matthews-Hunter. The Puysegur subduction zone (offshore New Zealand) is an ideal natural laboratory for testing the mechanics of subduction initiation with its well-constrained plate kinematics, structural controls, stress evolution, vertical motions, and distribution of faults.

These reconstructions provide essential initial and boundary conditions and allow for rigorous comparisons between geodynamic models and geological and geophysical observations. The finite element method will be used for the solution of these inherently time-dependent, multi-scale problems and achieve the resolutions required to track the localization of deformation key for systems with plastic failure.

The visco-elastoplastic models will have thermal and compositional buoyancy and explicit sub-scale models of weakening, dislocation creep, and partial melting. The team will constrain, slab strength, stress propagation, plastic failure and fault zone nucleation (weakening mechanisms associated with grain evolution and sperpentinization) from time-dependent models with plate motions for Puysegur since 15 Ma and Matthews-Hunter since 2 Ma.

The team will determine the conditions needed to initiate the IBM arc at 52 Ma over 100-1,000 km of strike such that the initial magmatic signal is synchronous within a few Myrs. For IBM, the rate at which driving forces grow and are transmitted to the Pacific plate will be addressed. The project will reach a new level of integration between dynamic flow models, plate kinematics and MG&G data that could have broad application.

The work could impact several large programs. The geodynamic hypotheses could result in predictions that could be tested with deep sea drilling under the auspices of IODP.

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.