Monitoring of phreatic eruptions using Interferometry on Retrieved Cross-Correlation Function from Ambient Seismic Noise: Results from Mt. Ruapehu, New Zealand
Monitoring of phreatic eruptions using Interferometry on Retrieved Cross-Correlation Function from Ambient Seismic Noise: Results from Mt. Ruapehu, New Zealand
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DOI：
10.1016/j.jvolgeores.2010.01.010
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发表时间：
2010-03-10
影响因子：
2.9
通讯作者：
Fournier, N.
中科院分区：
文献类型：
--
作者：
Mordret, A.;Jolly, A. D.;Fournier, N.
自1995-96年上次大规模喷发以来，鲁阿佩胡山已经喷发过两次，一次是2006年10月4日，一次是2007年9月25日。这些事件的发生没有任何明显的前兆，而且大多是潜水爆发。 “从环境地震噪声中检索互相关函数的干涉测量”（IRCASN）技术用于监测鲁阿佩胡山弹性特性的细微时间变化。通过计算火山周围几个站点记录的地震噪声的互相关函数，我们能够观察到 2006 年喷发期间的变化。参考互相关函数和当前互相关函数之间的比较使我们能够推断相对地震速度变化。从 2006 年喷发前两天开始，观测到该建筑的相对地震速度下降了 0.8%。这种下降是由于可逆且短暂的效应造成的，这可归因于鲁阿佩胡东侧下方的岩浆袋由于新岩浆进入小型储层而受到加压。这种压力增加导致鲁阿佩胡东侧膨胀，并打开该地区的裂缝，导致地震速度局部下降。我们对 2007 年的火山喷发进行了相同的分析，但没有观察到显着的地震速度变化。这种差异可能是由于两个事件的加压时间尺度不同以及 IRCASN 时间分辨率造成的。对这两次喷发之前的地震活动的分析使我们能够提出一个概念模型，该模型解释了 2006 年喷发的速度下降和 2007 年喷发缺乏速度变化。由于 GeoNet GPS 网络没有记录任何表面变形，因此我们对 5 公里深度处不产生变形的简单 Mogi 点源的最大半径和压力变化进行了建模。我们推断进入储层的最大新鲜岩浆体积约为 0.0017 km(3)，作为 GPS 地面变形测量的可检测阈值。 (C) 2010 Elsevier B.V. 保留所有权利。
Since the last major eruption in 1995-96 Mt. Ruapehu has erupted twice, on 4 October 2006 and on 25 September 2007. These events occurred without any clear precursors and were mostly phreatic explosions. The technique of "Interferometry on Retrieved Cross-Correlation Function from Ambient Seismic Noise" (IRCCASN) is used to monitor subtle temporal changes of Mt. Ruapehu's elastic properties. The computation of Cross-Correlation Functions of seismic noise recorded at several stations around the volcano allowed us to observe variations during the 2006 eruption period. The comparison between a Reference Cross-Correlation Function and a Current Cross-Correlation Function allows us to infer relative seismic velocity variations. A 0.8% decrease of relative seismic velocity in the edifice, starting two days before the 2006 eruption, was observed. This drop is due to a reversible and ephemeral effect, which can be attributed to a pressurization of a magma pocket beneath the east flank of Ruapehu due to new magma entering a small reservoir. This pressure increase produced an inflation of the east flank of Ruapehu and opened fractures in this area leading to a localised drop of seismic velocity. We conducted the same analysis for the 2007 eruption but no significant seismic velocity variation was observed. This difference is possibly due to the varying time scales of pressurization for the two events and also the IRCCASN time resolution. An analysis of the seismicity before these two eruptions allows us to propose a conceptual model which explains the velocity drop for the 2006 eruption and the lack of velocity variations for the 2007 eruption. Since there was no surface deformation recorded by the GeoNet GPS network, we modelled the maximum radius and pressure change for a simple Mogi point source at 5 km depth that produced no deformation. We inferred the maximum fresh magma volume of similar to 0.0017 km(3) entering the reservoir as a detectability threshold for GPS ground deformation measurements. (C) 2010 Elsevier B.V. All rights reserved.