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

MolnarEAR-9910145该项目建议在新西兰南岛北端的马尔伯勒地区安装10个便携式阵列，每个由11个三分量短周期地震仪组成，以测量地壳厚度和地壳和最上地幔的各向异性。其目的是量化走滑断层下方莫霍面的偏移量，并确定这些断层附近下地壳的广大区域是否发生了剪切。这种剪切是位于上地壳块体下方的下地壳韧性变形的预测结果，上地壳块体相互沿着走滑断层和在横向较宽区域剪切的地幔岩石圈运动。相反，如果断层直接从上地壳进入下地幔，则下地壳中几乎不存在各向异性，并且可能在走滑断层进入地幔的地方发生莫霍面的偏移。新西兰的马尔伯勒地区是一个绝佳的地点，因为：它是活跃的，断层上发生了大的位移；有丰富的局部中深地震活动，提供了具有陡峭入射角的高频体波；初步结果表明各向异性，尽管不是其深度范围。

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.