Collaborative Research: Quantifying the thermal effects of fluid circulation in oceanic crust entering the Cascadia subduction zone

合作研究：量化进入卡斯卡迪亚俯冲带的洋壳中流体循环的热效应俯冲带，在那里一个构造板块在另一个板块下方运动，产生世界上最大的地震和海啸。沿着分隔两个构造板块的俯冲带断层的温度影响摩擦，从而影响地震的大小和分布。此外，俯冲带的温度还会影响广泛的其他物理和化学过程，包括为一些火山提供燃料的岩浆的产生。为了理解这些过程，准确估计俯冲带温度是很重要的。在俯冲构造板块中循环的海水可能是俯冲带温度的重要控制因素。对于美国太平洋西北部近海的卡斯卡迪亚俯冲带，这种海水循环的空间范围和活力尚不为人所知，导致这一危险俯冲带的温度估计存在很大不确定性。这项研究将收集华盛顿州和俄勒冈州近海海底沉积物的温度测量结果，并绘制这些沉积物的分布图，以了解系统中对温度的控制，并改进对俯冲带温度的估计。这项研究的结果通过为地震风险估计提供信息，具有直接的社会效益。此外，拟议的项目将加强新墨西哥理工学院的教育，这是一家专注于STEM的拉美裔服务机构。两名研究生将接受地球物理和水文地质学方面的培训。该项目的成果将被纳入“在课堂上使用数据”的工作中，改善本科课程的实践体验。需要对俯冲带温度进行准确的估计，以了解各种关键过程，包括对俯冲巨型逆冲的孕震和抗震行为的控制。对于卡斯卡迪亚俯冲带，缺乏用仪器记录的板间地震活动，需要依赖间接方法(包括温度)来估计孕震带的范围。流体循环在俯冲板块内重新分配热量的程度对卡斯卡迪亚俯冲带的温度分布有着深远的影响。在卡斯卡迪亚，缺乏直接朝向海面的热通量数据是理解俯冲带温度的一个重大知识鸿沟。这项研究将通过收集华盛顿和俄勒冈州近海5个地点的~600公里地震反射线和~200个热流测量来填补这一空白，重点是量化胡安德·富卡板块热液循环的程度和活力。与基底起伏有关的热液环流在整个海底的热通量产生了很大的异常；这一信号为热液环流的存在提供了一种检验。综合来自多个地点的数据将提供关于热液循环是局部的还是区域性的信息。中心假设是：1)洋壳上层含水层中普遍存在热液循环；它持续存在于变形前缘附近被厚地幔覆盖的含水层和浅俯冲的地壳中；2)沿传播尾迹的假断层是贯穿整个地壳厚度的高渗透带；因此，相对于传播尾迹以外的区域，它们是流体和热循环增强的区域。将平均热流量值与岩石圈冷却模型预测的热流量值进行比较，将能够评估除了基本热通量之外，是否向系统添加了热量(例如，通过俯冲洋壳向海洋输送的热量和/或通过传播者尾迹中的断层向上平流的热量)。分析和解释Juan de Fuca板块在变形前沿附近的热状态控制将允许开发改进的俯冲区温度预测模型。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。

Collaborative Research: Quantifying the thermal effects of fluid circulation in oceanic crust entering the Cascadia subduction zoneSubduction zones, where one tectonic plate moves under another, generate the world’s largest earthquakes and tsunamis. Temperatures along the subduction zone fault that separates the two tectonic plates affect friction, thus influencing the size and distribution of earthquakes. In addition, subduction zone temperatures affect a wide range of other physical and chemical processes, including the generation of magma that supplies some volcanoes. To understand these processes, it is important to accurately estimate subduction zone temperatures. Seawater circulating in the subducting tectonic plate can be an important control on subduction zone temperatures. For the Cascadia subduction zone offshore the Pacific Northwest of the United States, the spatial extent and vigor of this seawater circulation is not well known, leading to substantial uncertainty in temperature estimates for this hazardous subduction zone. This study will collect temperature measurements in seafloor sediments offshore Washington and Oregon, and map the distribution of those sediments, to understand the controls on temperatures in the system and improve estimates of subduction zone temperatures. The results of this research have direct societal benefit, by informing earthquake hazard estimates. In addition, the proposed project will enhance education at New Mexico Tech, a STEM-focused Hispanic-serving institution. Two graduate students will be trained in geophysics and hydrogeology. Results of the project will be incorporated into “using data in the classroom” efforts, improving hands-on experience in undergraduate courses.Accurate estimates of subduction zone temperatures are required to understand a variety of critical processes, including controls on seismogenic and aseismic behavior on subduction megathrusts. For the Cascadia subduction zone, the dearth of instrumentally recorded interplate seismicity requires a reliance on indirect methods (including temperature) to estimate the extent of the seismogenic zone. The extent to which fluid circulation redistributes heat within the subducting plate has profound implications for temperature distributions in the Cascadia subduction zone. In Cascadia, a lack of heat flux data immediately seaward of the deformation front is a significant knowledge gap for understanding subduction zone temperatures. This study will fill this hole by collecting ~600 km of seismic reflection lines and ~200 heat flux measurements at 5 sites offshore Washington and Oregon with a focus on quantifying the extent and vigor of hydrothermal circulation in the Juan de Fuca plate. Hydrothermal circulation associated with basement relief generates large anomalies in heat flux across the seafloor; this signal provides a test for the presence of hydrothermal circulation. Combining data from multiple sites will provide information on whether hydrothermal circulation is local or regional. The central hypotheses are: 1) Hydrothermal circulation is ubiquitous in the upper oceanic crustal aquifer; it persists in the aquifer covered by a thick mantle of sediment near the deformation front and in the shallowly subducted crust; and 2) Pseudofaults along propagator wakes are zones of high permeability through the full thickness of the crust; thus, they are zones of enhanced fluid and heat circulation relative to areas outside of propagator wakes. Comparisons of mean heat flux values with those predicted from lithospheric cooling models will allow assessment of whether heat in addition to the basal heat flux is added to the system (e.g., heat transported seaward through the subducting oceanic crust and/or heat advected upwards through faults in propagator wakes). Analyzing and interpreting the controls on the thermal state of the Juan de Fuca plate near the deformation front will allow for the development of improved predictive models of subduction zone temperatures.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.