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 S-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 11km 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 δt 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 (11–14km) dacitic magma reservoir and a shallower (<5km) rhyolitic magma chamber. •During 2011 Santorini caldera exhibited signs of unrest.•In total 490 earthquakes were accurately relocated delineating a ring-fault.•Variations of Vp/Vs ratios signify periods of gas influx/depletion within cracks.•Decreasing delay splitting times during the unrest indicate closing of cracks.•Hypocenters support the view of one deep and one shallower magma reservoir. 出版者： Oxford: Elsevier B.V 出版日期： 2013-11-01 出處： Journal of volcanology and geothermal research, 2013-11, Vol.267, p.57-67 資源來源： Elsevier ScienceDirect Journals Complete 版權： 2013 Elsevier B.V. 版權： 2015 INIST-CNRS 識別號： ISSN: 0377-0273 識別號： EISSN: 1872-6097 識別號： DOI: 10.1016/j.jvolgeores.2013.10.001 識別號： CODEN: JVGRDQ
