Hikurangi Trench Regional Electromagnetic Survey to Image the Subduction Thrust

新西兰的Hikurangi俯冲带(HSZ)是太平洋构造板块沿着东海岸潜入北岛地壳之下的地方。HSZ的地震活动和板块滑动沿其长度显示出显着的变化：在南部，板块似乎是锁定的，有能力引发大地震，而在北部，板块正在蠕动，经常发生幕式缓慢滑动事件和偶尔发生的海啸地震。在平板联轴器中，控制这种对比的物理条件还不是很清楚。最近的研究表明，流体可能起到关键作用。为了描述流体是否对沿HSZ表达的滑动类型起主要控制作用，本研究将使用电磁(EM)方法来成像HSZ的电阻率结构。我们的测量将通过量化HSZ的孔隙度和流体预算沿和跨走向的变化，为水文结构提供重要的约束。该项目将支持一名博士生和几名研究生、博士后和早期职业科学家参与实地工作。PI是一名早期职业科学家，他将获得领导实地项目和指导研究生的宝贵经验。此外，将为学生和没有资助的合作者提供海洋电磁短期课程，以学习海洋电磁理论、应用、数据处理和反向建模。该项目将使用新证明的海洋电磁成像技术来约束HSZ两个部分的地壳和地幔的孔隙度和流体预算。调查巡航将在400公里乘150公里的区域内部署海底电磁接收器网格，该区域横跨来袭板块和弧前边缘。大地电磁(MT)响应函数将根据记录的电场和磁场时间序列进行估计。此外，受控源电磁(CSEM)数据将通过沿位于HSZ南段、中部和北段的三个海沟横断面在海底附近深度拖曳水平电偶极子发射器来记录。MT和CSEM数据将被用于电阻率的反演，并用于量化边缘的孔隙度结构。HSZ的电阻率结果将结合现有和计划中的地球物理和钻井数据进行解释，以检验地震活动和板间锁定沿走向的变化与进入的大洋板块的流体平衡、沿板块界面的流体含量以及上板块渗透率/孔隙度结构有关的假设。MT数据还将成像岩石圈和软流圈的电阻率，为岩石圈-软流圈边界的起源提供独立的约束。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Hikurangi subduction zone (HSZ) of New Zealand is where the Pacific tectonic plate dives beneath the crust of the North Island along its eastern coast. The HSZ displays marked changes in seismicity and plate-slip along its length: to the south the plates appear to be locked and have the capacity to generate great earthquakes whereas to the north the plates are creeping and regularly host episodic slow slip events and the occasional tsunami earthquake. The physical conditions controlling this contrast in plate coupling is not well understood. Recent investigations suggest fluids may play a critical role. To delineate whether fluids act as a primary control on the style of slip expressed along the HSZ, this study will use electromagnetic (EM) methods to image the electrical resistivity structure of the HSZ. Our measurements will provide important constraints on the hydrologic architecture by quantifying the along and across-strike variations in porosity and the fluid budget of the HSZ. This project will support a Ph.D. student and several graduate students, postdocs and early career scientists will be involved in the field work. The PI is an early career scientist who will gain valuable experience leading the field project and mentoring a graduate student. Additionally, a marine EM short-course will be given for students and unfunded collaborators to learn about marine EM theory, applications, data processing, and inverse modeling.This project will use newly proven marine EM imaging technology to constrain the porosity and fluid budget of the crust and mantle along both segments of the HSZ. The survey cruise will deploy a grid of ocean-bottom EM receivers in a 400 km by 150 km area that spans the incoming plate and fore-arc margin. Magnetotelluric (MT) response functions will be estimated from the recorded electric and magnetic field time-series. In addition, controlled-source EM (CSEM) data will be recorded by deep towing a horizontal electric dipole transmitter near the seafloor along three trench-crossing transects located in the southern, central, and northern segments of the HSZ. The MT and CSEM data will be inverted for electrical resistivity and used to quantify the porosity structure across the margin. The HSZ resistivity results will be interpreted in conjunction with existing and planned geophysical and drilling data to test the hypothesis that along-strike variations in seismicity and interplate locking are related to the fluid budget of the incoming oceanic plate, fluid content along the plate interface, and upper plate permeability/porosity structure. The MT data will also image the electrical resistivity of the lithosphere and asthenosphere, providing independent constraints on the origin of the lithosphere-asthenosphere boundary.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.