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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Seismicity, Vp/Vs and shear wave anisotropy variations during the 2011 unrest at Santorini caldera, southern Aegean
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Seismicity, Vp/Vs and shear wave anisotropy variations during the 2011 unrest at Santorini caldera, southern Aegean

机译：爱琴海南部圣托里尼火山口2011年动乱期间的地震活动度，Vp / Vs和剪切波各向异性变化

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摘要

The Santorini caldera has been the focus of several large explosive eruptions in the past, the last of which occurred in the early 1950s. The volcano was dormant until early 2011 when increasing number of earthquakes accompanied significant intra-caldera uplift. This seismic activity was recorded by 8 temporary as well as 19 permanent seismic stations that were installed on Santorini and nearby islands after the onset of the unrest Using data from January 2011 until June 2012 we calculated accurate relative locations for 490 events utilizing both catalog and waveform cross-correlation differential travel times of P- and 5-phases. The distribution of relocated events exhibits a large cluster between Thera and Nea Kameni islands along the caldera rim, suggesting the activation of a preexisting ring fault. All hypocenters are located between 5 and 11 km resulting in a sharp cutoff of seismicity above and below these depths. We also used P and S travel times in order to calculate average Vp/Vs ratios and estimated shear wave splitting parameters (fast direction Φ, delay time δt) for events within the shear wave window. The Vp/Vs ratios at several stations exhibit a majority of values consistently below the regional one (～1.77). Their temporal variations can be explained as periods of gas influx and depletion in the upper crust beneath the caldera. A comparison of fit for a number of earthquake doublets shows a progressive decrease of delay times towards the end of the unrest probably as a result of cracks closing owing to stress relaxation. The seismological observations presented here are compatible with petrological models that suggest the existence of a deep (11-14 km) dacitic magma reservoir and a shallower (＜5 km) rhyolitic magma chamber.
机译：过去，圣托里尼火山口一直是数起大型爆炸性爆炸的焦点，最后一次爆炸发生在1950年代初。火山一直处于休眠状态，直到2011年初，随着火山口内部隆升，地震数量不断增加。动乱发生后，在圣托里尼岛和附近岛屿上安装的8个临时地震台和19个永久地震台站记录了该地震活动。使用2011年1月至2012年6月的数据，我们利用目录和波形计算了490个事件的准确相对位置P相和5相的互相关差分行进时间。重新分布的事件的分布在沿着火山口边缘的塞拉岛（Thera）和尼阿卡梅尼岛（Nea Kameni）之间表现出很大的簇集，表明已经存在的环形断裂被激活。所有震源都位于5至11 km之间，从而导致这些深度以上和以下的地震活动急剧中断。我们还使用了P和S传播时间来计算平均Vp / Vs比率和估计的剪切波窗口内事件的剪切波分裂参数（快速方向Φ，延迟时间δt）。在几个站点的Vp / Vs比显示出的大多数值始终低于区域站点的值（〜1.77）。它们的时间变化可以解释为破火山口下方上地壳的瓦斯涌入和耗尽期。对多个地震双峰的拟合比较表明，到动乱结束时延迟时间逐渐减少，这可能是由于应力松弛导致的裂缝闭合所致。这里介绍的地震观测结果与岩石学模型相吻合，岩石学模型表明存在一个深层（11-14 km）的胶泥岩浆储层和一个浅层（＜5 km）的流纹岩浆腔。

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