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

使用表面波断层扫描 3D 各向异性速度模型研究太平洋西北地区的地幔动力学

• 批准号: 2224229
• 负责人: Aibing Li
• 金额: $ 16.78万
• 依托单位: University of Houston
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-10-01 至 2024-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2224229&HistoricalAwards=false
• 关键词: Investigating; Mantle; Dynamics; Pacific; Northwest

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.

太平洋西北地区 (PNW) 处于独特的地质环境中，海洋胡安德富卡 (JDF) 板块正在俯冲到北美板块之下。据信，JDF 板块至少在 2000 万年以来就与黄石热点相互作用。以前，在美国西北部产生普遍的火山活动，板块俯冲和板块-热点相互作用是太平洋西北地区地表地质的驱动力，包括火山和地震的排列。蛇河平原（SRP）中的年龄渐进火山（热点轨迹）呈西南-东北走向，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层地幔的地幔柱，就像然而，高熔岩平原 (HLP) 中的火山在西北方向形成了一条热点轨迹，这与双峰热点轨迹的机制相悖。太平洋西北地区的大量岩浆活动仍然存在争议，之前的美国西北部地震速度模型提高了对该地区复杂地质的认识。地震波的速度还取决于其传播方向，即地震各向异性。因此，对地震各向异性进行成像对于了解地球的动态地幔过程至关重要。太平洋西北地区的 3D 地震各向异性模型可解决板块与热点相互作用及其对广泛火山活动的影响。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。该项目将培训一名研究生和一名本科生。研究成果将通过会议、期刊和网站与科学界以及休斯顿大学本科生和研究生课程的学生分享。海洋板块俯冲、弧后火山活动和热点活动塑造了太平洋西北地区的地质历史，利用 USArray 可移动阵列 (TA) 的数据开发了许多高分辨率地震模型，提高了我们对构造的认识。然而，沿 SRP 和 HLP 分布的岩浆活动的来源究竟是地幔柱还是侵入的热海洋软流圈尚无定论。速度异常意味着该地区存在复杂的小规模地幔对流，这在当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。研究人员将利用来自地震记录的瑞利波和洛夫波数据构建高分辨率各向异性模型。这些模型中的 TA 和其他共存台站的径向和方位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可能的机制。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。