SIMULTANEOUS ANALYSES OF SEISMIC AND ACOUSTIC SIGNALS ASSOCIATED WITH VOLCANIC ERUPTIONS FOR UNDERSTANDING ERUPTION DYNAMICS

这项研究的目标是开发一种新的分析工具，对伴随火山喷发的地震和声波信号进行分析，以了解火山喷发的动力学。地震信号反映了火山导管的动态状态，而声波信号反映了注入大气的炽热火山物质的注入速度。不同的研究人员分别对每个信号进行了分析。在这项研究中，我开发了一个工具来同时分析这两种类型的信号。本研究分为三个部分：1)开发声波信号分析工具；2)将新开发的声波信号分析工具与已有的地震信号分析工具相结合；3)将新开发的工具应用于与大地电磁有关的地震信号和声波信号。本文对2004年阿萨玛火山喷发的地震信号和声波信号进行了波形分析。阿萨玛火山喷发概述如下。根据地震信号，估计了施加在火山管上的垂直单力的幅度。通过对声波信号的分析，估计了热火山物质向大气中注入速度的变化。对这两种信号的分析结果的比较表明，两种信号之间的幅度比在不同的喷发之间有很大的差异。例如，2004年9月1日的喷发具有强声学信号和弱地震信号的特征，而9月23日的喷发则具有相反的特征。具有不同厚度的火山导管帽的模型可以解释观测到的振幅比的变化。由该模型预测的盖层厚度变化与观测到的陨石坑底部高程的变化是一致的，后者与盖层厚度的变化成正比。

The goal of this research is developing a new analysis tool of the seismic and acoustic signals accompanying a volcanic eruption, to understand the eruption dynamics. Seismic signals reflect the state of dynamics in the volcanic conduit, while acoustic signals reflect injection rates of hot volcanic material injected into the atmosphere. Each signal has been separately analyzed by various researchers. In this research, I have developed a tool to analyze both types of signals simultaneously. This research is divided into three parts: 1) to develop an analyses tool for acoustic signals, 2) to combine the newly developed analyses tool of acoustic signals with the pre-existing analyses tool of seismic signals, 3) to apply the newly developed tool to the seismic and acoustic signals associated with Mt. Asama eruptions in 2004.The results of the wave form analyses of both seismic and acoustic signals of Mt. Asama eruptions are summarized as follows. From the seismic signals, amplitudes of the vertical single-forces exerted on the volcanic conduit were estimated. From the analyses of the acoustic signals, changes in the injection rate of hot volcanic material into the atmosphere were estimated. The comparison of the results of the analyses of both types of signals revealed that the amplitude ratio between the two signals vary significantly from eruption to eruption. For example, the eruption in September 1st, 2004 is characterized by strong acoustic signals and weak seismic signals, while the eruption in September 23rd has the opposite character. A model with varying thickness of the cap of the volcanic conduit can explain the observed variation of the amplitude ratio. The cap thickness variation predicted by this model is in good agreement with the observed change in the elevation of the crater bottom which is proportional to the change in the cap thickness.