Publication Date:
2020-07-24
Description:
The present study is focused on the examination of the state of the recently activated Santorini VolcanicComplex (SVC) area, located in the Southern Aegean Sea. The seismic activity was investigated in detailand different methodologies have been applied to examine whether the SVC area approached an eruptivephase during the 2011–2012 seismic crisis period. The detailed spatiotemporal analysis for the broaderstudy area revealed two different seismic patterns: low seismic activity until 2010, mainly concentratedwithin the Anydros basin and close to the submarine volcano, Columbo, and activation during 2011 and2012 of two previously quiescent regions. The first is the Santorini Caldera, which had been active formore than one year, and the second is the area south of Christiana Islands, which was activated in January2012 with the occurrence of two major events of magnitude 5.1 and 5.2, respectively, followed by a largenumber of aftershocks.In this study, manual analysis and relocation of the 2011–2012 seismic crisis in the SVC was performed,in order to obtain a high-resolution image of the activated structures. The seismicity within the SantoriniCaldera, which is oriented approximately NE-SW, was rapidly diminished after the activation of theChristiana area. A large number of focal mechanisms were determined which mainly indicated strike-slip faulting inside the Caldera. Furthermore, the fault plane solutions of the major events in the areasouth of Christiana, derived by waveform modeling, also suggested similar type of faulting. This typediffers from the normal faults observed in the Anydros basin. However, the stress field in all cases isconsistently oriented in a NW-SE direction. Since the Santorini Volcano was seismically activated forthe first time after the 1950 eruption, changes of the physical properties of the medium were examinedusing different approaches to assess the state of the volcano. The shear-wave splitting analysis revealedthe existence of an anisotropic upper crust, while no significant temporal variations of the anisotropydirection were observed. The majority of the recorded events were classified as volcano-tectonic micro-earthquakes using spectral analysis. Nevertheless, certain cases of spasmodic bursts and LF events, whichcan be related to magma activity, have also been identified. A region of low Vsand high Vp/Vsratio hasbeen detected north of Nea Kammeni, at depths between 3 and 5 km, that is directly associated with themagmatic chamber inside the Caldera. The applied multi-method approach revealed that the SantoriniVolcano was activated, while the obtained results indicate that the Volcano did not reach a critical stateduring the 2011–2012 unrest period.
Type:
Article
,
PeerReviewed
Format:
text
Permalink