Collaborative Research: Controlled source seismic investigation of the top of the Yellowstone magmatic system

关于黄石火山系统，最重要的谜团之一是，它目前是否含有上层地壳岩浆，其熔体成分足够高，可以在人类的时间尺度上喷发。先前对黄石火山口下结构的成像提供了潜在的相互矛盾的证据，一些研究表明岩浆不太可能喷发，另一些研究表明岩浆接近可喷发范围，但只存在于孤立的位置。这些研究依赖于自然震源（如地震）中相对较长的波长采样。该项目将使用可控震源、高频振动车和数百台密集分布的地震仪器来仔细检查黄石岩浆库的顶部，估计在地表以下约4-8公里。这一实验将为岩浆库顶部熔体的约束提供一个新的水平。此外，该项目将深入了解岩浆储层上方的热液流体分布，包括其深度范围和地表不同地热盆地之间的地下连通性程度。这个项目增加了年轻一代科学家对受控源研究项目的参与，提供与自然资源勘探工业有关的方法方面的培训。两名研究生将接受应用地震成像方面的培训。调查人员将与国家公园的工作人员合作，为黄石公园每年约400万游客提供非正式教育。该项目主要是为了测试黄石岩浆库顶部附近的地震速度是否与接近可喷发熔体部分的岩浆浓度一致。此外，它还将研究影响上地壳地震活动的岩浆挥发物的储层和路径，以及火山口内不同地热盆地的位置。解决这些问题的一种新能力将是通过控制源数据收集，通过三个分量的接收器阵列沿着两个密集采样的样带收集数据，这些样带的位置由先前的被动源成像研究指导。控制源反射成像和振幅与偏移量分析在硅质岩浆储层上很少可能，因为大多数储层太小或缺乏直接在储层上方的通道。在这种情况下，从被动震源成像推断的岩浆储层上方存在有利的道路横断面，其阵列更稀疏，频率更低。先前对上地壳储层中熔体成分的估计差异很大，而新的调查将有助于利用受控源P-to-P和P-to-S反射波的振幅来澄清可喷发岩浆的潜在存在和体积。Vp和Vs约束的组合还具有绘制岩浆挥发物地下聚集的潜力，这可能为地震活动性源区的物理性质和不同地热盆地的深层基础提供新的见解。该奖项反映了美国国家科学基金会的法定使命，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。

Among the most important mysteries regarding the Yellowstone volcanic system is whether it currently contains upper crustal magma with high enough melt fractions to be eruptible over human time scales. Prior imaging of the structure beneath Yellowstone caldera offers potentially conflicting evidence with some studies indicating magma that is unlikely to be eruptible and others indicating magma that is near the eruptible range but only present in isolated locations. These studies relied on relatively long wavelength sampling from natural seismic sources such as earthquakes. This project will use a controlled seismic source, a high-frequency vibrator truck, and hundreds of densely spaced seismic instruments to scrutinize the top of the Yellowstone magma reservoir, estimated to be about 4-8 km below the surface. This experiment will provide a new level on constraint on the melts at the top of the magma reservoir. Additionally, the project will gain insights on the distribution of hydrothermal fluids above the magma reservoir including their depth extent and the degree of subsurface connectivity among distinct geothermal basins at the surface. This project increases the involvement of younger generations of scientists in controlled source research projects, providing training in methods that are relevant to natural resource exploration industries. Two graduate students will be trained in applied seismic imaging. The investigators will engage with National Park personnel to advance informal education for Yellowstone’s approximately 4 million annual visitors.The project primarily seeks to test whether seismic velocities near the top of the Yellowstone magma reservoir are consistent with concentrations of magma approaching eruptible melt fractions. Additionally, it will investigate reservoirs and pathways for magmatic volatiles that influence upper crustal seismicity and the locations of distinct geothermal basins within the caldera. A new ability to address these questions will be provided by controlled source data collection with an array of 3-component receivers along two densely sampled transects whose locations are guided by prior passive source imaging studies. Controlled source reflection imaging and amplitude versus offset analysis are rarely possible above silicic magma reservoirs, because most are too small or lack road access directly above the reservoirs. In this case, favorable road transects exist above the magma reservoir inferred from passive source imaging with sparser arrays and lower frequencies. Prior estimates of melt fractions in the upper crustal reservoir vary widely, and the new survey will help clarify the potential presence and volume of eruptible magma using reflected wave amplitudes from controlled source P-to-P and P-to-S reflections. The combination of Vp and Vs constraints also has the potential to map subsurface accumulations of magmatic volatiles, which may provide new insights into the physical properties of the source regions of seismicity and deep underpinnings of distinct geothermal basins.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.