Hikurangi Trench Regional Electromagnetic Survey to Image the Subduction Thrust

新西兰的希库兰吉俯冲带（HSZ）是太平洋构造板块沿着沿着北岛东海岸俯冲到北岛地壳之下的地方。HSZ沿其长度沿着的地震活动性和板块滑动显示出显著的变化：南部的板块似乎被锁定，有能力产生大地震，而北部的板块蠕动，并定期举办幕式缓慢滑动事件和偶尔的海啸地震。控制板耦合中这种对比度的物理条件还没有很好地理解。最近的研究表明，液体可能起着关键作用。为了描述流体是否作为一个主要的控制方式的滑动表示沿着HSZ，本研究将使用电磁（EM）的方法来成像电阻率结构的HSZ。我们的测量将提供重要的限制水文结构量化的孔隙度和流体预算的HSZ的沿着和跨走向的变化。该项目将支持博士学位。学生和一些研究生，博士后和早期职业科学家将参与实地工作。PI是一名早期职业科学家，将获得领导现场项目和指导研究生的宝贵经验。此外，海洋EM短期课程将给予学生和未资助的合作者，学习海洋EM理论，应用，数据处理，和inverse modeling.This项目将使用新证明的海洋EM成像技术，以限制沿沿着HSZ的两个部分的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，该区域跨越传入板块和弧前边缘。大地电磁（MT）响应函数将估计从记录的电场和磁场的时间序列。此外，受控源EM（CSEM）数据将通过沿位于HSZ南部、中部和北方段的沿着三个跨沟断面在海底附近深拖水平电偶极发射器来记录。将对MT和CSEM数据进行电阻率反演，并用于量化边缘的孔隙结构。HSZ电阻率结果将结合现有和计划的地球物理和钻井数据进行解释，以检验地震活动性和板间锁定的沿走向变化与传入海洋板块的流体预算、沿着板块界面的流体含量和上板块渗透率/孔隙度结构有关的假设。MT数据还将对岩石圈和软流圈的电阻率进行成像，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.