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，它目前是否含有足够高的熔融分数的地壳上部岩浆，足以在人类时间尺度上喷发。先前对黄石火山口下结构的成像提供了可能相互矛盾的证据，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喷发范围，但只存在于孤立的地点。这些研究依赖于对地震等自然震源进行相对较长波长的采样。该项目将使用受控震源、高频可控震源卡车和数百台密集分布的地震仪器来仔细检查黄石岩浆水库的顶部，据估计，该水库位于地表以下约4-8公里处。这项实验将对岩浆库顶部熔体的约束提供一个新的水平。此外，该项目还将深入了解岩浆库上方热液的分布情况，包括其深度、程度和地表不同地热盆地之间的地下连通程度。该项目增加了年轻一代科学家对受控制来源研究项目的参与，提供与自然资源勘探行业相关的方法培训。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。该项目主要寻求测试黄石公园岩浆库顶部附近的地震速度是否与接近可喷发熔体分数的岩浆密度一致。此外，它还将调查影响地壳上部地震活动的岩浆挥发分的储集层和路径，以及火山口内不同地热盆地的位置。解决这些问题的新能力将由受控震源数据收集提供，该数据收集具有沿两个密集采样横断面的三分量接收器阵列，其位置由先前的被动震源成像研究指导。硅质岩浆储集层上方的可控源反射成像和幅度-偏移距分析几乎不可能，因为大多数太小或没有直接位于储集层上方的道路。在这种情况下，从阵列稀疏和频率较低的被动震源成像中推断出的岩浆储集层上方存在有利的道路横断面。此前对上地壳储集层熔体比例的估计差异很大，新的调查将有助于利用受控源P-to-P和P-to-S反射的反射波幅度来澄清潜在的可喷发岩浆的存在和体积。Vp和VS约束的组合也有可能绘制地下岩浆挥发分的累积图，这可能为地震活动源区的物理性质和不同地热盆地的深部基础提供新的见解。这一奖项反映了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。

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.