Stochastic modeling of seismic wave propagation beneath island-arcs and volcanoes

岛弧和火山下面的地壳和上地幔是非常不均匀的。速度层析成像分析揭示了俯冲洋板和地幔楔的精细构造等构造不均匀性。该方法基于纵波和横波起跳的走时读取，完全忽略了波形信息。尽管近年来利用新的密集地震台网数据提高了速度非均匀性的空间分辨率，但由于尺度长度比台站距离短得多，这种分析本身就难以成像短波长的非均匀性。与确定性方法相反，还有一种可选的随机方法。该项目的目的是提出理论模型来解释波在高度不均匀介质中的传播，并开发分析在岛弧和火山中观测到的高频地震记录的方法。我们使用解析方法和数值方法来研究随机介质中的波传播，其中我们引入了波动方程的统计处理。我们将与日本东北大学的研究伙伴合作，进一步发展现有的方法，并研究默拉皮火山的样本数据集。

The crust and the upper mantle beneath island arcs and volcanoes are known to be very heterogeneous. The structural inhomogeneity including the fine structure of the subducting oceanic slab and the mantle wedge has been revealed from velocity tomography analyses. This method, which is based on the travel time reading of P and S wave onsets, disregards waveform information completely. Even though the spatial resolution of the velocity inhomogeneity has been improved recently by using data of new dense seismic networks, it is inherently difficult for this analysis to image short wavelength heterogeneities with scale length much shorter than the station separation. In contrast to the deterministic approach, there is an alternative, stochastic approach. The objective of this project is to propose theoretical models to explain wave propagation through highly inhomogeneous media and to develop methods for analyzing high frequency seismograms observed in island arcs and volcanoes. We use both analytical methods and numerical methods for the study of wave propagation in randon media, where we introduce a statistical treatment of the wave equation. Existing methods will be further developed in cooperation with our Japanese research partners of Tohoku University, and sample data sets from Merapi volcano will be studied.