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其东海岸潜入北岛地壳之下的地方。HSZ在地震活动和板块滑动方面表现出明显的变化：向南的板块似乎是锁定的，有能力产生大地震，而向北的板块是蠕动的，经常发生间歇性的慢滑事件和偶尔的海啸地震。控制板耦合中这种对比的物理条件还没有得到很好的理解。最近的研究表明，液体可能起着关键作用。为了确定流体是否是沿HSZ滑动类型的主要控制因素，本研究将使用电磁（EM）方法对HSZ的电阻率结构进行成像。我们的测量将通过量化HSZ沿和沿走向的孔隙度变化和流体收支，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是一个早期的职业科学家，他将获得领导实地项目和指导研究生的宝贵经验。此外，将为学生和无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，数据处理和逆建模。该项目将使用最新的海洋电磁成像技术来限制HSZ两段地壳和地幔的孔隙度和流体收支。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，该区域横跨入射板块和弧前边缘。根据记录的电场和磁场时间序列估计大地电磁（MT）响应函数。此外，可控源电磁（CSEM）数据将通过深拖曳海底附近的水平电偶极子发射机，沿着位于HSZ南部、中部和北部的三个海沟穿越断面记录。将对MT和CSEM数据进行电阻率反演，并用于量化整个边缘的孔隙度结构。HSZ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，以验证地震活动性和板块间锁定的沿走向变化与进入的海洋板块的流体平衡、板块界面流体含量以及板块上部渗透率/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。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.