Stress field around the Coloumbo magma chamber,southern Aegean: Its significance for assessing volcanic and seismic hazard in Santorini |
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| Institution: | 1. Bulgarian Academy of Sciences, National Institute of Geophysics, Geodesy and Geography, Department of Geodesy, Acad. G. Bonchev str, bl. 3, 1113 Sofia, Bulgaria;2. University of Architecture, Civil Engineering and Geodesy, Faculty of Geodesy, Department of Geodesy and Geoinformatics, 1, Hristo Smirnenski Blvd., 1046 Sofia, Bulgaria;3. Ecole Normale Supérieure, PSL Research University, Laboratoire de Géologie - UMR CNRS 8538, 24 Rue Lhomond, 75005 Paris, France;4. National Observatory of Athens, Institute of Geodynamics, Lofos Nymfon, Thission, 11810 Athens, Greece;5. National Observatory of Athens, Institute of Astronomy, Astrophysics, Space Applications and Remote Sensing, Vas. Pavlou & I. Metaxa, GR-15 236 Penteli, Greece;6. Aristotle University of Thessaloniki, School of Geology, Department of Physical and Environmental Geography, 54124 Thessaloniki, Greece;1. United Schmidt Institute of the Physics of the Earth, Russian Academy of Sciences, ul. BoVshaya Gruzinskaya 10, Moscow, 123995, Russia;2. Science Station of the Russian Academy of Sciences, Bishkek, 720049, Kyrgyzstan;1. Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK;2. Department of Geology and Geophysics, SOEST, University of Hawaii, Honolulu, HI 96822, USA |
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| Abstract: | Coloumbo submarine volcano lies 6.5 km offshore the NE part of the Santorini island complex and exhibits high seismicity along with vigorous hydrothermal activity. This study models the local stress field around Coloumbo's magma chamber and investigates its influence on intrusion emplacement and geometry. The two components of the stress field, hoop and radial stress, are calculated using analytical formulas that take into account the depth and radius of the magma chamber as these are determined from seismological and other observations. These calculations indicate that hoop stress at the chamber walls is maximum at an angle of 74° thus favouring flank intrusions, while the radial stress switches from tensile to compressive at a critical distance of 5.7 km from the center of the magma chamber. Such estimates agree well with neotectonic and seismological observations that describe the local/regional stress field in the area. We analyse in detail the case where a flank intrusion reaches the surface very near the NE coast of Thera as this is the worst-case eruption scenario. The geometrical features of such a feeder dyke point to an average volumetric flow rate of 9.93 m3 s?1 which corresponds to a Volcanic Explosivity Index of 3 if a future eruption lasts about 70 days. Hazards associated with such an eruption include ashfall, ballistic ejecta and base surges due to explosive mixing of magma with seawater. Previous studies have shown that areas near erupting vents are also foci of moderate to large earthquakes that precede or accompany an eruption. Our calculations show that a shallow event (3–5 km) of moment magnitude 5.9 near the eruptive vent may cause Peak Ground Acceleration in the range 122–177 cm s?2 at different locations around Santorini. These values indicate that seismic hazard even due to a moderate earthquake near Coloumbo, is not trivial and may have a significant impact especially on older buildings at Thera island. |
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