Advances in seismic imaging of magma and crystal mush
Advances in seismic imaging of magma and crystal mush
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DOI：
10.3389/feart.2022.970131
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发表时间：
2022-10
期刊：
影响因子：
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通讯作者：
M. Paulatto;E. Hooft;K. Chrapkiewicz;B. Heath;D. Toomey;J. Morgan
中科院分区：
文献类型：
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作者：
M. Paulatto;E. Hooft;K. Chrapkiewicz;B. Heath;D. Toomey;J. Morgan
地震成像方法为岩浆系统的物理性质提供了详细的三维约束，从而对岩浆的储存、分化和动力学提供了宝贵的见解。这些限制对我们对岩浆系统的现代理解的发展至关重要。然而，由于火山地震成像固有的挑战，仍然存在突出的知识空白。这些挑战源于与岩浆储层相关的高度非均质低速异常波传播的复杂物理特性。基于射线的地震成像方法，如走时层析成像和表面波层析成像，导致对这种速度异常的恢复不足，并导致对熔体成分的估计不足。这篇综述旨在帮助火山学家充分利用地震成像所获得的见解，并解释分辨率的限制。我们总结了最常见的成像方法的优点和局限性，并提出了它们的实施和低速异常定量解释的最佳实践。我们建立并分析了78个弧、热点和大陆裂谷火山的277个地震成像研究数据库。每项研究都附有有关震源、使用的部分波场、成像方法、任何检测到的低速带和估计的熔体分数的信息。39项研究试图估计22座不同火山的熔体成分。只有五项研究发现，在临界孔隙度以上的熔体部分存在熔体储存的证据，而临界孔隙度是将晶体浆糊与流动岩浆分开的标准。熔体分数的中位数为13%，表明岩浆储存以低熔体分数的结晶糊状岩浆为主。然而，由于地震分辨率的限制，地震证据不能排除在许多被研究的火山上存在小型（<10 km3）和中型（<100 km3）高熔体部分岩浆房。多种层析成像方法的结合，以及更广泛地采用比第一次到达的旅行时间使用更多地震波场的方法，有望克服地震层析成像的一些局限性，并提供更可靠的熔体分数约束。为了实现岩浆储层成像的革命，需要更广泛地采用这些新方法和数据收集方面的进展。
Seismic imaging methods have provided detailed three-dimensional constraints on the physical properties of magmatic systems leading to invaluable insight into the storage, differentiation and dynamics of magma. These constraints have been crucial to the development of our modern understanding of magmatic systems. However, there are still outstanding knowledge gaps resulting from the challenges inherent in seismic imaging of volcanoes. These challenges stem from the complex physics of wave propagation across highly heterogeneous low-velocity anomalies associated with magma reservoirs. Ray-based seismic imaging methods such as travel-time and surface-wave tomography lead to under-recovery of such velocity anomalies and to under-estimation of melt fractions. This review aims to help the volcanologist to fully utilize the insights gained from seismic imaging and account for the resolution limits. We summarize the advantages and limitations of the most common imaging methods and propose best practices for their implementation and the quantitative interpretation of low-velocity anomalies. We constructed and analysed a database of 277 seismic imaging studies at 78 arc, hotspot and continental rift volcanoes. Each study is accompanied by information about the seismic source, part of the wavefield used, imaging method, any detected low-velocity zones, and estimated melt fraction. Thirty nine studies attempted to estimate melt fractions at 22 different volcanoes. Only five studies have found evidence of melt storage at melt fractions above the critical porosity that separates crystal mush from mobile magma. The median reported melt fraction is 13% suggesting that magma storage is dominated by low-melt fraction crystal mush. However, due to the limits of seismic resolution, the seismological evidence does not rule out the presence of small (<10 km3) and medium-sized (<100 km3) high-melt fraction magma chambers at many of the studied volcanoes. The combination of multiple tomographic imaging methods and the wider adoption of methods that use more of the seismic wavefield than the first arriving travel-times, promise to overcome some of the limitations of seismic tomography and provide more reliable constraints on melt fractions. Wider adoption of these new methods and advances in data collection are needed to enable a revolution in imaging magma reservoirs.