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Research on Magma Migrating and Plumbing Process in the Precursory Period of Volcanic Eruptions

火山喷发前期岩浆运移及管道过程研究

基本信息

批准号：
17340128
负责人：
MORITA Yuichi
金额：
$ 4.94万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2007
项目状态：
已结题

项目摘要

We analyzed seismic and geodetic data simultaneously to reveal the magma emplacement and plumbing process for the volcanoes in the Precursory P to the following eruptions in future. We mainly analyzed the process at Eastern Cost of Izu Peninsula and Izu-Oshima volcano. The former is characterized by repeated earthquake swarms, which were accompanied with a submarine eruption. The later is in the step of preparing the eruption in future because summit inflations accompanied with increase of seismicity are observed every a few years recently.From the systematic analysis of earthquake swarms at the eastern coast of lzu Peninsula, we reveal that the swarm activities are composed of upward migration of two kinds of magma driven by buoyancy, because the hypocenters distinctly separate in the depth. The deeper activity ranged from 7 to 9 km in depth otherwise shallower one did from 3 to 7km. The earthquakes are generated by stress concentration at the tip of the dikes and the hypocenters in t … More he swarms reflect the size of dikes On the other hand, the ground deformation shows the excess pressure in the dike. The joint analysis of the seismic and geodetic data, we found out that the excess pressure in deeper dikes have systematically higher than that of the shallower one. The systematic difference in the excess pressure at the same region has not been found in the previous studies, and it is one of the unique results in this study We discussed also on reasons on the systematic difference, and conclude that the condition of the tip cavity of the dike controls the condition of the dike intrusion process and it leads the systematic difference in the excess pressure.From joint analysis of seismic and geodetic data at Izu-Oshima volcano, we found out that seismic activities are categorized into two groups. One is the seismicity occurring beneath the Izu-Oshima caldera, and the other is occurring around the coast of the island. The seismic activity beneath caldera is well synchronized with volcanic edifice inflation and deflation. The observed ground deformation in the inflation and deflation matches well with the model of point source with spherical model. In the previous studies, the ground deformation was thought to be caused by volume increase of magma chamber whose shape is approximately a sphere located beneath the caldera. From precise hypocentral distribution, and focal mechanisms of the earthquakes, we proposed the other magma sources that are composed of two dikes with different azimuth, which well fits with the data of ground deformation. Our model has several advantages in observational facts because it is supported not only by seismic and geodetic data, but also by a model of stress field caused by wide-ranged tectonic stress and heterogenous structure around the summit vent. Our model is more realistic and helpful to understand the precursory process to volcanic eruptions.As mentioned above, we got valuable results in this study. The image of magma migration and plumbing in the precursory process of volcanic eruptions becomes more concrete and animation-like in our model. We would like to develop the study on the magma emplacing and accumulation based on the results in this study. Less

我们同时分析了地震和大地测量数据，以揭示岩浆侵位和铅垂过程的火山在前兆P到未来的喷发。主要分析了伊豆半岛东海岸和伊豆大岛火山的喷发过程。前者的特点是多次发生震群，并伴有海底喷发。通过对伊豆半岛东海岸震群的系统分析，揭示了由于震源在深度上明显分离，震群活动是由两种岩浆在浮力驱动下向上运移而成。较深的活动范围为7 - 9 km，较浅的活动范围为3 - 7 km。这些地震是由岩墙尖端和震源处的应力集中引起的。 ...更多信息震群反映了岩脉的大小，而地面变形则反映了岩脉内部的超压。通过对地震和大地测量资料的联合分析，发现深堤坝的超压比浅堤坝的超压有系统性的增大。同一区域超压的系统性差异在以往的研究中没有发现，这是本研究的独特结果之一，并对系统性差异的原因进行了讨论。通过地震和大地测量联合分析，认为堤顶空洞的条件控制了堤体侵入过程的条件，并导致了超压的系统差异根据伊豆大岛火山的地震活动数据，我们发现地震活动分为两组。一个是伊豆大岛破火山口下发生的地震活动，另一个是发生在岛屿海岸周围的地震活动。火山口下的地震活动与火山建筑物的膨胀和收缩很好地同步。观测到的膨胀和收缩过程中的地面形变与点源模型和球模型吻合较好。在以往的研究中，地面变形被认为是由位于破火山口下方的近似球形岩浆房体积增大引起的。从精确的震源分布、震源机制等方面，提出了由两个不同方位的岩脉组成的岩浆源，与地面形变资料吻合较好。我们的模型在观测事实上有几个优点，因为它不仅得到了地震和大地测量数据的支持，而且还得到了广泛的构造应力和非均匀结构的应力场模型所造成的高峰喷口周围。我们的模型更符合实际，有助于理解火山爆发的演化过程，得到了有价值的结果。在我们的模型中，火山喷发的岩浆迁移和垂直运动的图像变得更加具体和动画化。希望在此基础上进一步开展岩浆侵位和聚集的研究。少