Precursory characteristics of the seismicity before the 6 August 2012 eruption of Tongariro volcano, North Island, New Zealand
Precursory characteristics of the seismicity before the 6 August 2012 eruption of Tongariro volcano, North Island, New Zealand
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DOI：
10.1016/j.jvolgeores.2014.03.004
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发表时间：
2014-10-01
影响因子：
2.9
通讯作者：
Sherburn, Steven
中科院分区：
文献类型：
--
作者：
Hurst, Tony;Jolly, Arthur D.;Sherburn, Steven
2012年8月6日，汤加里罗火山的上蒂马里火山口爆发，此前约有三周的地震活动。地震迁移，包括额外的临时站的数据表明，几乎所有的事件都在一个小区域非常接近上特马里。这些重新定位的地震大多非常浅，几乎所有的事件都在地表以下1000 - 1500 m。在2012年7月12-13日的第一个震群中，所有地震的事件间时间一致，为71 +/- 8分钟，而在后来的震群中（7月17-20日和29-30日），许多事件的事件间时间一致。平稳准周期（“发条”）地震过程表明，一个单一的破裂点是由一个几乎恒定的速率通量过程激发。在这些震群中观察到的主要地震类型具有尖锐的开始和广泛的频谱，具有2至10 Hz的强能量。大多数事件的局部震级为1.5至2.5级，几乎没有较小的事件。这些地震中的大多数似乎属于一个主震族，其特征包括约2 Hz的强谱分量和间隔约1.5 s的三次能量爆发。在116次定位地震中，75次与主事件的相关系数大于0.70。这些事件的频谱不随大小而变化，所有事件的匹配频率峰值具有高相关性。最后一次此类事件发生在2012年8月6日火山爆发的前一天，此后再也没有发生过此类事件，汤加里罗火山下的地震活动也很少。这次地震活动提醒了GNS科学和其他组织注意汤加里罗的动荡，并提高了火山警报级别和航空颜色代码以宣传这一点。GNS科学公司还增加了对汤加里罗的监测，发现岩浆气体浓度比2012年5月的测量结果有所增加。然而，地震活动没有显示出任何加速趋势，表明有立即爆发的威胁，这表明很难预测汤加里罗和类似火山的小规模爆发。(C)2014爱思唯尔有限公司版权所有。
The 6 August 2012 eruption from the Upper Te Maari crater of Tongariro volcano followed approximately three weeks of precursory seismic activity. Earthquake relocations including data from extra temporary stations indicated that nearly all events were in a small area very close to Upper Te Maari. Most of these relocated events were very shallow, with nearly all events being between 1000 and 1500 m below the ground surface.The pre-eruption seismicity occurred in three main swarms. During the first swarm on 12-13 July 2012, all the earthquakes had consistent inter-event times of 71 +/- 8 min, while in the later swarms (17-20 and 29-30 July) many events had a similar pattern of consistent inter-event times. The stationary quasi-periodic ("clockwork") earthquake process suggests that a single fracture point was excited by a nearly constant rate flux process. The dominant type of earthquake observed in these swarms had a sharp onset and a broad spectrum, with strong energy from 2 to 10 Hz. Most events seen had a local magnitude of 1.5 to 2.5, with virtually no smaller events. Most of these earthquakes appeared to belong to a main earthquake family whose characteristics included a strong spectral component at about 2 Hz and three bursts of energy spaced at intervals of about 1.5 s. Of the 116 located earthquakes, 75 had a correlation coefficient greater than 0.70 with a master event. The spectra of these events did not change with size, with matching frequency peaks for all the events with a high correlation. The last event of this type was the day before the 6 August 2012 eruption, none have been seen since and there has been very little seismicity under Tongariro.This seismicity alerted GNS Science and other organisations to the unrest of Tongariro, and the Volcanic Alert Level and Aviation Colour Code were raised to publicise this. GNS Science also increased its monitoring of Tongariro, and discovered that the magmatic gas concentrations had increased compared to previous measurements in May 2012. However, the seismicity did not show any accelerating trend that suggested an immediate eruption threat, indicating the difficulty of predicting small eruptions in Tongariro and similar volcanoes. (C) 2014 Elsevier B.V. All rights reserved.