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 - 99101445本项目拟在新西兰南岛北端的马尔堡地区安装10个便携式阵列，每个阵列由11个3分量短周期地震仪组成，用于测量地壳厚度和地壳和上地幔的各向异性。目的是确定走滑断层下莫霍断层的偏移量，并确定在这些断层附近的下地壳的广大地区是否发生过剪切。这种剪切是上地壳板块下地壳韧性变形的预测结果，这些板块沿着走滑断层和地幔岩石圈相互移动，在横向宽的区域上被剪切。相反，如果断层直接从上地壳进入下地幔，则下地壳的各向异性很少或根本不存在，并且在走滑断层进入地幔的地方可能会出现莫霍断层的偏移。新西兰的马尔堡地区是一个绝佳的位置，因为：它是活跃的，断层上发生了大位移；有丰富的局部中深度地震活动性，提供大入射角的高频体波；初步结果表明各向异性，但深度范围不明确。

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.