Intellectual Merit of Research. - The Marlborough strike slip fault system of New Zealand clearly exemplifies the transition in plate convergence from near decoupling between upper and lower plates in true subduction (northern North Island), to essentially complete coupling between the plates with near-continuous thickening of the crust and upper mantle and no subduction (central South Island). In Marlborough, four major dextral fault zones at a low angle to the present Australian-Pacific plate convergence direction accommodate most of the component of motion parallel to the plate boundary. A magnetotelluric (MT) geophysical transect of the region is to be carried out to clarify controls on internal physical state of strike slip fault zones, and fill a gap in understanding of transpressional orogens between uncoupled and fully coupled situations. Basic questions to be addressed include: 1) How much are seismogenic faults fluidized, which may influence stress buildup?, 2) Is the fluid state of fault zones a function of cumulative displacement or degree of activity?, 3) Do major fault zones acquire their fluids locally, or from the lower crust?, 4) What are the physical conditions in the crust as major strike slip faults initiate?, 5) What enables coupling between subducting and overriding plates to develop?, 6) Is the subduction interface sharp, or is there a broad zone of diffuse deformation?, 7) If fluids help control rheology near the subduction interface, what is their origin?, and 8) Do slab dehydration reactions contribute to seismicity of the downgoing slab? Broader Impacts of the Research. - The proposal is a fully cooperative effort between the University of Utah of the United States and the Institute of Geological and Nuclear Sciences (IGNS) of New Zealand in research into an important solid earth problem. Support for a female graduate student is made available for education into state of the art geophysical instrumentation, parameters of field survey design, practical logistical matters in overseas settings, modern methods of inversion, and the relationship between electrical resistivity and physico-chemical state in the Earth. The utility of off-the-shelf commercial geophysical instrumentation for specialized solid earth studies is tested and the project raises the profile of electrical methods, an underutilized field, in solid earth science. Additional societal benefits include broader understanding of the controls on fault strength and ability to build up damaging stresses.
