COLLABORATIVE RESEARCH: Deformation of the Lower Crust Beneath Strike-Slip Faults: Array Studies of Anistropy and Converted Phases in the Marlborough Fault Zone of New Zealand

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MolnarEAR-9910145This project proposes to install ten portable arrays, each consisting of eleven 3-component, short-period seismographs, in the Marlborough region at the northern end of the South Island of New Zealand to measure both crustal thickness and anisotropy in the crust and uppermost mantle. The goal is to quatify the offset of the Moho below strike-slip faults and to determine whether shear has occurred over broad regions in the lower crust near such faults. Such shear is a predicted consequence of ductile deformation in the lower crust lying beneath blocks of upper crust that move with respect to one another along strike-slip faults and mantle lithosphere that is sheared over a laterally wide zone. Conversely, if faults passed directly from the upper crust into the lower mantle, little or no anisotropy would be present in the lower crust, and possible an offset of the Moho would occur where strike-slip faults pass into the mantle. The Marlborough region of New Zealand is an excellent location because: it is active and large displacements have occurred on the faults; there is abundant local intermediate depth seismicity to provide high-frequency body waves with steep angles of incidence; and preliminary results indicate anisotropy, although not its depth range.