Deformation, Fluid Generation, and Seismogenesis in a Transitional Subduction Environment, the Marlborough Region, New Zealand, Revealed with a Magnetotelluric Resistivity Transect

研究的智力价值。-新西兰马尔堡走滑断裂系统清楚地体现了板块汇聚从真正俯冲（北岛北部）的上下板块接近解耦，到地壳和上地幔接近连续增厚但没有俯冲（南岛中部）的板块基本完全耦合的转变。在马尔堡，四个与当前澳大利亚-太平洋板块辐合方向成低角度的主要右断裂带容纳了大部分平行于板块边界的运动分量。为了明确走滑断裂带内部物理状态的控制因素，并填补不耦合和完全耦合情况下对跨震造山带认识的空白，将对该地区进行大地电磁地球物理样带研究。需要解决的基本问题包括：1)有多少发震断层流化，这可能会影响应力的积累？2)断裂带的流体状态是累积位移或活动程度的函数吗？(3)主要断裂带的流体是本地获得的，还是来自下地壳？4)主要走滑断层发生时，地壳内部的物理条件是什么？(5)是什么使得俯冲板块和上覆板块之间的耦合得以发展？(6)俯冲界面是尖锐的，还是大面积的扩散变形带？7)如果流体有助于控制俯冲界面附近的流变性，那么它们的来源是什么？8)底板脱水反应是否对下行底板的地震活动性有贡献？研究的更广泛影响。-这项建议是美国犹他大学和新西兰地质与核科学研究所在研究一个重要的固体地球问题方面的充分合作努力。为一名女研究生提供教育支持，使其了解最先进的地球物理仪器、实地调查设计参数、海外环境中的实际后勤问题、现代反演方法以及地球电阻率与物理化学状态之间的关系。在专门的固体地球研究中测试了现成的商业地球物理仪器的效用，该项目提高了固体地球科学中未充分利用的电方法的轮廓。额外的社会效益包括更广泛地理解对断层强度的控制和建立破坏性应力的能力。

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.