Nature of a Low Velocity Anomaly in the Mantle Transition Zone Beneath the Western Great Plains

地质科学领域数十年的深入研究令人信服地表明，大规模的地表地貌，如山脉、海盆和裂谷;以及地震和火山爆发等自然灾害，都是地球内部深处发生的动力过程的表现。其中一个过程是地幔中比正常温度更高的部分熔融岩石的上涌。近年来，一些地球物理研究已经确定了西部大平原下的这种上升流，但几何形状，深度范围，更重要的是，形成机制，这一功能仍然是谜。这项研究将采用一套计算密集型地球物理技术来调查这一有趣的特征。这项研究的结果将揭示地球上其他地方的类似特征，最终提高我们理解，预测和减轻自然灾害以及有效探索和开发自然资源的能力。拟议的科学调查将对来自广泛领域和职业阶段的地球科学家产生重大影响。一名研究生、两名本科生和一名暑期实习生将参与这项研究。从这个项目中开发的材料将被整合到大学的各种教育计划中，旨在招募少数民族本科生和研究生进入科学事业。研究小组将使用一系列地震学方法来调查西部大平原下一个突出的低速异常的存在和性质，通过测试三个假设，包括1）它是否代表一个异常热，低密度，与Farallon板块俯冲有关的上涌特征; 2）起源于下地幔的新兴地幔柱; 3）地幔过渡带的高含水量区。测试假设的研究任务包括速度校正明显的过渡区不连续的深度，获得使用P-S接收器功能;成像地幔过渡区使用多次反射P-S转换;调查地震各向异性分层;和约束异常功能使用合成测试。测试这些假设可能会提供一阶约束地球动力学模型，从而在理解北美构造演化的重大进展。该奖项反映了NSF的法定使命，并已被认为是值得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的支持。

Decades of intensive research in the geological sciences have convincingly shown that large-scale surface features such as mountain belts, ocean basins, and rifted valleys; and natural hazards such as earthquakes and volcanic eruptions; are manifestations of dynamic processes occurring in the deep interior of the Earth. One of these processes is the upwelling of hotter-than-normal, partially melted rocks in the Earth’s mantle. In recent years, a number of geophysical studies have identified such upwelling beneath the western Great Plains, but the geometry, depth extent, and more importantly, formation mechanism for this feature remain enigmatic. This study will employ a suite of computationally-intensive geophysical techniques to investigate this intriguing feature. Findings from this study will shed light on similar features elsewhere on Earth, ultimately improving our capability to understand, predict, and mitigate natural hazards and effectively explore and develop natural resources. The proposed scientific investigations will have significant impacts for geoscientists from a wide range of fields and career stages. A graduate student, two undergraduate students, and a summer intern will be involved in the study. Materials developed from this project will be integrated into various educational programs at the university aimed at recruiting minority undergraduate and graduate students into scientific careers.The research team will use an array of seismologic approaches to investigate the existence and nature of a prominent low velocity anomaly beneath the western Great Plains by testing three hypotheses, including whether it represents 1) an anomalously hot, low-density, upwelling feature associated with the subduction of the Farallon slab; 2) an emerging plume originating from the lower mantle; and 3) a zone of high water content in the mantle transition zone. Research tasks to test the hypotheses include velocity corrections to the apparent transition zone discontinuity depths, obtained using P-to-S receiver functions; imaging the mantle transition zone using multiply reflected P-to-S conversions; investigation of seismic anisotropy layering; and constraining the anomaly feature using synthetic tests. Testing these hypotheses may provide first-order constraints for geodynamic models, leading to significant progress in understanding the tectonic evolution of North America.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.