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首页> 外文期刊>Journal of Volcanology and Geothermal Research >A new source process for evolving repetitious earthquakes at Ngauruhoe volcano, New Zealand
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A new source process for evolving repetitious earthquakes at Ngauruhoe volcano, New Zealand

机译：新西兰Ngauruhoe火山不断演变的地震的新来源过程

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Since early 2005, Ngauruhoe volcano has produced repeating low-frequency earthquakes with evolving waveforms and spectral features which become progressively enriched in higher frequency energy during the period 2005 to 2009, with the trend reversing after that time. The earthquakes also show a seasonal cycle since January 2006, with peak numbers of events occurring in the spring and summer period and lower numbers of events at other times. We explain these patterns by the excitation of a shallow two-phase water/gas or water/steam cavity having temporal variations in volume fraction of bubbles. Such variations in two-phase systems are known to produce a large range of acoustic velocities (2-300 m/s) and corresponding changes in impedance contrast We suggest that an increasing bubble volume fraction is caused by progressive heating of melt water in the resonant cavity system which, in turn, promotes the scattering excitation of higher frequencies, explaining both spectral shift and seasonal dependence. We have conducted a constrained waveform inversion and grid search for moment, position and source geometry for the onset of two example earthquakes occurring 17 and 19 January 2008, a time when events showed a frequency enrichment episode occurring over a period of a few days. The inversion and associated error analysis, in conjunction with an earthquake phase analysis show that the two earthquakes represent an excitation of a single source position and geometry. The observed spectral changes from a stationary earthquake source and geometry suggest that an evolution in both near source resonance and scattering is occurring over periods from days to months.
机译：自2005年初以来，Ngauruhoe火山产生了重复的低频地震，其波形和频谱特征不断演变，并在2005年至2009年期间逐渐丰富了高频能量，此后趋势开始逆转。自2006年1月以来，地震还显示出一个季节性周期，春季和夏季发生的事件数量最高，而在其他时间发生的事件数量较少。我们通过激发浅的两相水/气体或水/蒸汽腔来解释这些模式，这些气泡具有气泡体积分数的时间变化。众所周知，两相系统中的这种变化会产生很大的声速范围（2-300 m / s），并且阻抗反差会相应变化。我们建议，气泡体积分数的增加是由于共振中融化水的逐渐加热而引起的空腔系统，进而促进了更高频率的散射激发，从而解释了光谱偏移和季节依赖性。我们对2008年1月17日至19日发生的两次示例地震的发生进行了受限的波形反演和网格搜索，以寻找弯矩，位置和震源几何形状，此时事件表明几天内发生了一次频率富集事件。反演和相关的误差分析，再加上地震相位分析表明，两次地震代表了单个震源位置和几何形状的激发。从固定地震源和几何结构观察到的频谱变化表明，从几天到几个月的时间里，近震源共振和散射都发生了演变。

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