Extreme seismic anisotropy indicates shallow accumulation of magmatic sills beneath Yellowstone caldera
Extreme seismic anisotropy indicates shallow accumulation of magmatic sills beneath Yellowstone caldera
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极端地震各向异性表明黄石火山口下方岩浆岩床浅层堆积
DOI：
10.1016/j.epsl.2023.118244
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发表时间：
2023
影响因子：
5.3
通讯作者：
Schmandt, Brandon
中科院分区：
文献类型：
--
作者：
Wu, Sin-Mei;Huang, Hsin-Hua;Lin, Fan-Chi;Farrell, Jamie;Schmandt, Brandon
了解现代岩浆系统中晶体糊状物的分布和流动性对于火山灾害评估至关重要，因为移动岩浆的不同区域可能会相互连接，并导致比广泛分布在均匀糊状物中的岩浆在更短的时间尺度上熔化积聚。在这里，我们揭示了黄石公园顶部 20 公里的上地壳岩浆储层在熔体浓度和结构上都是不均匀的。我们利用前所未有的密集临时地震网络中的环境噪声来联合约束垂直和水平偏振剪切波速度，以创建增强的 3D 各向同性和各向异性剪切速度模型。我们的模型显示了地表以下 4-7 公里处的异常低速（>20% 减少）层，位于先前通过地震 P 波断层扫描成像的水库顶部附近。该层内存在强烈的径向各向异性（20％），表明现代黄石储层的最上部被组织为基岩复合体，在过去喷发前通常储存流纹岩的深度处，水平拉长体积中的熔体分数高达 28％。研究结果表明，通过密集地震网络进行高分辨率各向异性成像可以限制岩浆分布和储层结构，这对于了解黄石等火山系统的演化和危险评估非常重要。
Understanding the distribution and mobility of crystal mushes within modern magmatic systems is crucial to volcanic hazard assessments as distinct pockets of mobile magma may become interconnected and lead to melt accumulation on shorter time scales than magma that is broadly distributed in a homogeneous mush. Here, we reveal that Yellowstone's upper-crustal magma reservoir in the top 20 km is heterogeneous in both melt concentration and texture. We exploit ambient noise in an unprecedented dense temporary seismic network to jointly constrain vertically- and horizontally-polarized shear wave speeds to create enhanced 3D isotropic and anisotropic shear velocity models. Our models show an exceptionally low-velocity (>20% reduction) layer 4–7 km beneath the surface, situated near the top of the reservoir previously-imaged by earthquake P-wave tomography. The presence of strong radial anisotropy (20%) within this layer indicates the uppermost portion of the modern Yellowstone reservoir is organized as a sill complex, with up to 28% of melt fraction in horizontally-elongated volumes at depths where rhyolite was commonly stored before past eruptions. The findings demonstrate that high-resolution anisotropic imaging through a dense seismic network can constrain both magma distribution and reservoir texture, which are important to understand the evolution and hazard assessment of volcanic systems like Yellowstone.