Rock fracture as a precursor to lava dome eruptions at Mount St Helens from June 1980 to October 1986
Rock fracture as a precursor to lava dome eruptions at Mount St Helens from June 1980 to October 1986
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DOI：
10.1007/s00445-006-0102-5
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发表时间：
2007-04-01
影响因子：
3.5
通讯作者：
Sammonds, P. R.
中科院分区：
文献类型：
--
作者：
Smith, R.;Kilburn, C. R. J.;Sammonds, P. R.
继 1980 年 5 月 18 日普林尼式喷发之后，圣海伦火山（美国华盛顿州）进入了间歇性熔岩穹顶挤压时期，直到 1986 年。在重新挤压之前，地震活动速率不断加快，在随后的喷发之前观测到更多的前兆地震活动。这里使用失效预测方法（FFM）来研究观测到的火山构造（VT）地震活动率的变化。分析表明：(1) 所有 VT 危机均在 3 周内（通常不到 10 天）导致火山喷发，(2) 大多数火山喷发都有 VT 前兆，(3) 前兆地震活动模式显示出围绕理想模型趋势的波动。因此，尽管这些地震事件可用于警告即将发生的火山喷发，但具体预测仍存在数周或更长时间的不确定性。有人提出：（1）后来喷发之前的地震活动增加是由于更大、更凝固的穹顶对岩浆上升产生了更大的阻碍； (2) 导致火山喷发的地震群的一致性表明，只有在火山喷发已经开始时，才会达到足以引发围岩和熔岩穹顶甲壳破裂的应力； (3) 加速岩石破裂模型与观测到的地震活动之间可能存在差异，因为大量岩石通过延性机制而不是震源破裂而变形。
Following its plinian eruption on 18 May 1980, Mount St Helens (Washington State, USA) entered a period of intermittent lava-dome extrusion until 1986. Renewed extrusion was frequently preceded by accelerating rates of seismicity, with more precursory seismicity observed prior to eruptions later in the sequence. Here the failure forecasting method (FFM) is used to investigate changes in the observed rate of volcano-tectonic (VT) seismicity. The analysis indicates that: (1) all VT crises resulted in an eruption within 3 weeks (usually less than 10 days), (2) the majority of eruptions had VT precursors, and (3) patterns of precursory seismicity showed fluctuations about the ideal model trend. Thus, although these seismic events could be used to warn of an impending eruption, specific forecasts were subject to an uncertainty of weeks or more. It is proposed that: (1) increased seismicity prior to later eruptions is a result of a larger and more solidified dome acting as a greater impediment to magma ascent; (2) the consistency of seismic swarms resulting in an eruption indicates that stresses high enough to initiate fracturing in the country rock and lava dome carapace were only achieved once the approach to an eruption had already begun; and (3) discrepancies between models of accelerating rock fracture and the observed seismicity may arise due to a significant amount of the rocks deforming through ductile mechanisms rather than seismogenic fracture.