STUDY ON SOURCE PROCESS OF VERY LONG PERIOD SEISMIC EVENTS

特长周期地震事件震源过程研究

• 批准号: 11640404
• 负责人: NISHIMURA Takeshi
• 金额: $ 2.18万
• 依托单位: TOHOKU UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11640404/
• 关键词: very long period seismic events; magmatic fluid; moment tensor inversion; source process; magma chambers; 長周期地震; 岩手山; マグマ溜り; 圧縮性流体; 広帯域地震観測; 火山

I studied source process of very long period seismic events that have recently been observed at many active volcanoes. I deployed four to six broad band seismometers and a low-frequency microphone around Mounts Iwate and Bandai, northeastern Japan. The two volcanoes have recently shown significant crustal deformations and/or micro earthquake activities, so I successfully recorded high quality data of very long period seismic events of the two volcanoes. Examining the observed waveform characteristics, I determined the locations and space-time functions of moment tensors of the seismic source that excites long period signals of about 10 s. The results show that : (1) the sources for Mount Iwate events are located in a region having a high Vp/Vs ratio that indicates an existence of magmatic fluid ; (2) the source mechanisms of very long period events observed at both of the two volcanoes indicate mutual inflation and deflation motions. Such source mechanisms are also reported for the ver … More y long period seismic events at other active volcanoes such as Mount Aso. I, therefore, conclude that the source mechanisms of very long period events includes significant volumetric changes. To explain the observed source mechanisms and the dominant periods of the oscillations, I presented a source model in which compressible fluid motions in an irregular dike or volcanic pipe are expressed by the basic equations for a one-dimensional fluid dynamics. Calculations of the motions using a finite difference method indicate that two chambers connected by a narrow channel can act as an inflation and deflation seismic source. The long period waves of 10 s are easily excited by narrowing the channel without unrealistic large magma chambers and/or magmatic fluid having extremely low acoustic velocity. Based on my analyses of the observed waveforms and theoretical considerations, I conclude that the very long period seismic events are excited by a migration of magmatic fluid in volcanic dikes or pipes with an irregular shape. Less

我研究了最近在许多活火山观测到的超长周期地震事件的震源过程。我在日本东北部的岩手山和万代山周围部署了四到六个宽带地震仪和一个低频麦克风。这两座火山最近表现出明显的地壳变形和/或微地震活动，因此我成功记录了两座火山的极长周期地震事件的高质量数据。通过检查观测到的波形特征，我确定了激发约 10 秒长周期信号的震源矩张量的位置和时空函数。结果表明：（1）岩手山事件的震源位于Vp/Vs比值较高的区域，表明存在岩浆流体； (2) 两座火山观测到的极长周期事件的源机制表明相互的膨胀和紧缩运动。阿苏山等其他活火山的长期地震事件也有类似的震源机制。因此，我得出的结论是，超长周期事件的源机制包括显着的体积变化。为了解释观察到的震源机制和振荡的主要周期，我提出了一个震源模型，其中不规则岩堤或火山管中的可压缩流体运动由一维流体动力学的基本方程表示。使用有限差分法对运动的计算表明，通过狭窄通道连接的两个腔室可以充当膨胀和紧缩地震源。通过缩小通道很容易激发 10 s 的长周期波，而无需不切实际的大型岩浆室和/或具有极低声速的岩浆流体。根据对观测波形的分析和理论考虑，我得出的结论是，极长周期地震事件是由不规则形状的火山岩脉或管道中的岩浆流体的运移激发的。较少的

项目成果

Takeshi Nishimura, Haruhisa Nakamichi, Satoru Tanaka, Minemori Sato, Tomokatsu Kobayashi, Sadato Ueki, Hiroyuki Hamaguchi, Masakazu Ohtake, and Haruo Sato: "Source Process of very long period seismic events associated with the 1998 activity of Iwate Volca

Takeshi Nishimura、Haruhisa Nakamichi、Satoru Tanaka、Minemori Sato、Tomokatsu Kobayashi、Sadato Ueki、Hiroyuki Hamaguchi、Masakazu Ohtake 和 Haruo Sato：“与 1998 年岩手火山活动相关的超长周期地震事件的来源过程”

Takeshi Nishimura et al.: "Source Process of very long period seismic events associated with the 1998 activity of Iwate Volcano, northeastern Japan"Journal of Geophysical Rosearch. 105. 19135-19147 (2000)

Takeshi Nishimura 等人：“与 1998 年日本东北部岩手火山活动相关的极长周期地震事件的来源过程”地球物理研究杂志。

Takeshi Nishimuna et al.: "Source process of very long period seismic events associated with the 1998 activity of Iwate Volcano, northeastern Japan"Journal of Geophysical Research. 105. 19135-19147 (2000)

Takeshi Nishimuna 等人：“与 1998 年日本东北部岩手火山活动相关的极长周期地震事件的震源过程”地球物理研究杂志。