Janiszewski Helen A, Wagner Lara S, Roman Diana C
Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC, United States.
Department of Earth Sciences, University of Hawai'i at Mānoa, Honolulu, HI, United States.
Sci Rep. 2020 Feb 4;10(1):1780. doi: 10.1038/s41598-020-58589-0.
Processes related to eruptions at arc volcanoes are linked by structures that transect the entire crust. Imaging the mid- to lower-crustal portions (here, ~5-15 km and >15 km respectively) of these magmatic systems where intermediate storage may occur has been a longstanding challenge. Tomography, local seismic source studies, geodetic, and geochemical constraints, are typically most sensitive to shallow (<5 km) storage and/or have insufficient resolution at these depths. Geophysical methods are even further limited at frequently-erupting volcanoes where well-developed trans-crustal magmatic systems are likely to exist, due to a lack of deep seismicity. Here we show direct evidence for mid-crustal magma storage beneath the frequently erupting Cleveland volcano, Alaska, using a novel application of seismic receiver functions. We use P-s scattered waves from the Moho as virtual sources to investigate S-wave velocities between the Moho and the surface. Our forward modeling approach allows us to provide direct constraints on the geometry of low velocity regions beneath volcanoes despite having a comparatively sparse seismic network. Our results show clear evidence of mid-crustal magma storage beneath the depths of located volcanic seismicity. Future work using similar approaches will enable an unprecedented comparative examination of magmatic systems beneath sparsely instrumented volcanoes globally.
与弧火山喷发相关的过程由贯穿整个地壳的构造联系在一起。对这些岩浆系统中可能发生中间储存的中地壳至下地壳部分（此处分别约为5 - 15千米和大于15千米）进行成像一直是一项长期挑战。层析成像、局部地震源研究、大地测量和地球化学约束，通常对浅部（<5千米）储存最为敏感，和/或在这些深度分辨率不足。由于缺乏深部地震活动，地球物理方法在频繁喷发的火山中受到的限制更大，而这些火山很可能存在发育良好的跨地壳岩浆系统。在此，我们利用地震接收函数的一种新应用，展示了阿拉斯加频繁喷发的克利夫兰火山下方中地壳岩浆储存的直接证据。我们将来自莫霍面的P波散射波用作虚拟震源，来研究莫霍面与地表之间的S波速度。尽管地震台网相对稀疏，但我们的正演模拟方法使我们能够对火山下方低速区域的几何形状提供直接约束。我们的结果清楚地表明，在已定位的火山地震活动深度之下存在中地壳岩浆储存。未来使用类似方法开展的工作，将能够对全球仪器配备稀疏的火山下方的岩浆系统进行前所未有的对比研究。
