Investigating Mantle Dynamics in the Pacific Northwest Using 3D Anisotropic Velocity Models from Surface Wave Tomography

太平洋西北地区(PNW)处于独特的地质环境中，大洋Juan de Fuca(JDF)板块正俯冲到北美板块之下。据信，至少从2000万年前开始，JDF板块就与黄石热点相互作用，在美国西北部产生了普遍的火山活动。板块俯冲和板块-热点相互作用是PNW地表地质的驱动力，包括火山和地震。蛇河平原(SRP)演化火山(热点轨迹)的走向为西南-NE向，与北美板块的板块运动一致，表明黄石热点可能是起源于深部地幔的热柱，与夏威夷热点一样。然而，与羽流假说相反，高熔岩平原(HLP)的火山在NW方向形成了一个热点轨迹。PNW的双峰热点轨迹和大量岩浆活动的机制仍在争论中。之前美国西北部的地震速度模型提高了人们对该地区复杂地质的理解。地震波的速度还取决于它的传播方向，称为地震各向异性，这与岩石圈变形和地幔流动有关。因此，地震各向异性成像是了解地球动力学地幔过程的关键。研究人员将在太平洋西北部建立一个高分辨率的3D地震各向异性模型，以解决板块-热点相互作用及其对大范围火山活动的贡献。该模型还有助于了解和监测该地区的地震活动和火山喷发。该项目将对一名研究生和一名本科生进行地震数据处理和层析成像方法方面的培训。研究结果将通过会议、期刊和网站与科学界分享，并与休斯顿大学研究人员本科生和研究生课程的学生分享。休斯顿大学是一家为少数族裔服务的机构。大洋板块俯冲、弧后火山活动和热点活动塑造了太平洋西北部的地质历史。许多高分辨率地震模型都是使用美国阵列移动阵列(TA)的数据开发的，这提高了我们对该地区构造和地球动力学的理解。然而，沿SRP和HLP广泛分布的岩浆活动的来源是地幔热柱还是侵入热的大洋软流圈仍未得到解决。许多局部速度异常表明该地区存在复杂的小尺度地幔对流，这在目前横向或垂直分辨率有限的各向异性模型中尚未得到证实。研究人员将利用TA和美国西北部其他共存台站记录的地震瑞利波和乐夫波数据构建高分辨率各向异性模型。这些模型中径向和方位向各向异性的分辨率与各向同性速度的分辨率相似，有助于揭示详细的地幔动力学过程，并测试太平洋西北部地球物理观测的可能机制。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 Pacific Northwest (PNW) is in a unique geological setting, where the oceanic Juan De Fuca (JDF) plate is subducting under the North American plate. It is believed that the JDF slab has interacted with the Yellowstone hotspot since at least 20 million years ago, generating pervasive volcanism in the northwestern United States. The plate subduction and the slab-hotspot interaction are the driving forces for the surface geology in the PNW, including volcanoes and earthquakes. The alignment of age-progressive volcanos (hotspot track) in the Snake River Plain (SRP) is SW-NE, agreeing with the plate motion of the North American plate, suggesting the Yellowstone hotspot is probably a plume that originates from the deep mantle, like the Hawaii hotspot. However, the volcanos in the High Lava Plains (HLP) form a hotspot track in the NW direction, against the plume hypothesis. The mechanisms for the bimodal hotspot tracks and the voluminous magmatism in the PNW are still under debate. Previous seismic velocity models beneath the northwestern United States have improved the understanding of the complex geology in the area. The velocity of a seismic wave also depends on its propagation direction, called seismic anisotropy, which is associated with lithospheric deformation and mantle flow. Therefore, imaging seismic anisotropy is critical to understanding the dynamic mantle process of the earth. The investigator will produce a high-resolution, 3D seismic anisotropy model in the Pacific Northwest to address the slab-hotspot interaction and its contribution to the extensive volcanism. The model is also helpful in understanding and monitoring seismicity and volcano eruptions in the area. The project will train one graduate and one undergraduate student in seismic data processing and tomography methods. The research results will be shared with the scientific community through conferences, journals, and websites and with students in the investigator’s undergraduate and graduate courses at the University of Houston, a minority serving institution. Oceanic plate subduction, back-arc volcanism, and hotspot activity have shaped the geological history of the Pacific Northwest. Many high-resolution seismic models have been developed using data from the USArray Transportable Array (TA), improving our understanding of tectonics and geodynamics in the region. However, whether the source of the widespread magmatism along the SRP and HLP is from a mantle plume or intruding hot oceanic asthenosphere is not resolved. Many local velocity anomalies imply complex small-scale mantle convection in the region, which has not been verified in current anisotropic models with limited lateral or vertical resolution. The investigator will construct a high-resolution anisotropic model using Rayleigh and Love wave data from earthquakes recorded at the TA and other coexisting stations in the northwestern United States. The resolution for radial and azimuthal anisotropy in these models is similar to that for isotropic velocity, helping reveal detailed mantle dynamic processes and test possible mechanisms for geophysical observations in the Pacific Northwest.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.