NSF East Asia and Pacific Summer Institute (EAPSI) for FY 2013 in New Zealand

Nevitt Johanna M, Stanford CA

Investigators

Abstract

----- This action funds Johanna M. Nevitt of Stanford University to conduct a research project in the Geosciences area during the summer of 2013 at the University of Otago in Dunedin, New Zealand. The project title is "Improving Numerical Models of Fault Deformation at the Crustal Scale." The host scientist is Dr. Virginia G. Toy. Numerical models of fault-related deformation are built upon a number of physical equations, including constitutive equations that define how rock deforms in response to stress. Implementing accurate constitutive equations is essential to producing significant and reliable model results. Rocks located within fault-zones may creep (i.e., deform viscously) in either a grain size sensitive (GSS) or grain size insensitive (GSI) manner, which is believed to result in either aseismic (steady-state) slip or seismic (earthquake-producing) slip on faults, respectively. Constitutive equations for GSS and GSI creep are currently poorly constrained, which limits our ability to model fault-related deformation, particularly at the crustal scale. This project determines appropriate constants for GSS and GSI creep constitutive equations by analyzing samples collected by scientific drilling into New Zealand?s Alpine Fault Zone. Microchemical and microstructural maps, created using energy-dispersive x-ray spectroscopy (EDX) and electron backscatter diffraction (EBSD) analysis of the samples, reveal whether deformation occurred via GSS or GSI creep. The maps can then be imported into Elle, a modeling platform for simulating the two-dimensional evolution of microstructures in a polycrystalline material during and following deformation. Numerical experiments are conducted in Elle to determine the constants for the creep constitutive equations that best simulate the fabrics observed in the samples. Dr. Toy will eventually use these parameterized constitutive equations in crustal scale numerical models of the earthquake cycle on the Alpine Fault. Broader impacts of an EAPSI fellowship include providing the Fellow a first-hand research experience outside the U.S.; an introduction to the science, science policy, and scientific infrastructure of the respective location; and an orientation to the society, culture and language. These activities meet the NSF goal to educate for international collaborations early in the career of its scientists, engineers, and educators, thus ensuring a globally aware U.S. scientific workforce. Upon returning to the U.S., the fellow will share what she learned with current and future users of Stanford's EBSD lab by creating a quartz-specific EBSD manual and leading a seminar on strategies specific to analyzing and modeling quartz deformation. This will be valuable, since no faculty members at Stanford are currently using EBSD analysis or numerical methods to study quartz deformation. In addition, the fellow will share her experience studying the Alpine Fault in New Zealand through "Geokids," a Stanford University outreach program that teaches basic earth science to elementary school children. In a more formal sense, the results of this project will be disseminated at the American Geophysical Union Fall Meeting in San Francisco in December 2013, and will be published in a peer-reviewed journal.