Recent geodetic unrest at Santorini Caldera, Greece

Abstract

After approximately 60 years of seismic quiescence within Santorini caldera, in January 2011 the volcano reawakened with a significant seismic swarm and rapidly expanding radial deformation. The deformation is imaged by a dense network of 19 survey and 5 continuous GPS stations, showing that as of 21 January 2012, the volcano has extended laterally from a point inside the northern segment of the caldera by about 140 mm and is expanding at 180 mm/yr. A series of spherical source models show the source is not migrating significantly, but remains about 4 km depth and has expanded by 14 million m3since inflation began. A distributed sill model is also tested, which shows a possible N‐S elongation of the volumetric source. While observations of the current deformation sequence are unprecedented at Santorini, it is not certain that an eruption is imminent as other similar calderas have experienced comparable activity without eruption.

Volcanic Hazard Assessment at Santorini Volcano: A Review and a Synthesis in the Light of the 2011-2012 Santorini Unrest

“…The increased seismicity was accompanied by up to 10 cm inflation of the islands measured by GPS networks and by radar interferometry, corresponding to a modelled volume increase of about 10-20 million m 3 at 3-6 km beneath the northern caldera basin (Newman et al, 2012;Parks et al, 2012;Papoutsis et al, 2013;Foumelis et al, 2013). Small increases in the fluxes of H2 and mantle-derived CO2 also occurred during the unrest (Parks et al, 2013;Tassi et al, 2013).…”

“…The volume increase associated with deformation was attributed to intrusion of magma and associated fluids (Newman et al, 2012;Parks et al, 2012). Both volume and gas composition changes may also have been in part tectonic in origin due to stress accumulation on regional faults (Feullet, 2013) caused by flexuring of the caldera block and increasing rock permeability and hence gas emissions (Tassi et al, 2013).…”

“…The number of small-magnitude (M < 3.6) volcanotectonic earthquakes greatly increased during the 15-month-long unrest period at depths of 1-6 km on a near-vertical 6 km-long plane along the Kameni line (Newman et al, 2012). The increased seismicity was accompanied by up to 10 cm inflation of the islands measured by GPS networks and by radar interferometry, corresponding to a modelled volume increase of about 10-20 million m 3 at 3-6 km beneath the northern caldera basin (Newman et al, 2012;Parks et al, 2012;Papoutsis et al, 2013;Foumelis et al, 2013).…”

“…The ISMOSAV monitoring network recorded changes in the monitored parameters (seismicity, topographic changes, thermal state, chemistry of the hot fluids and soil gases; Tassi et al, 2013), and campaign measurements also detected changes in soil gas fluxes and compositions (Parks et al, 2013;Rizzo et al, 2015). In addition, GPS networks (Newman et al, 2012) and satellite radar observations detected ground uplift at rates approaching 1 cm/month on parts of the Kameni islands (Parks et al, 2012Foumelis et al, 2013;Lagios et al, 2013), with higher (but unmeasured) uplift rates possibly occurring under water. All of these changes exceeded the limits defining the background state of the Kamenis volcanic center, based on the monitoring network data for the last 20 years.…”

Focal mechanism and depth of the 1956 Amorgos twin earthquakes from waveform matching of analogue seismograms

“…During the last 60 yr the Santorini volcano exhibited only weak background seismicity (Dimitriadis et al, 2005(Dimitriadis et al, , 2009Bohnhoff et al, 2006;Hensch, 2009), except for a period of unusually high seismicity lasting from January 2011 to January 2012, with local magnitudes up to 3.2 accompanied by surface deformations within the Caldera as a result of magma upwelling (Newman et al, 2012;Chouliaras et al, 2012;Vallianatos et al, 2013). In contrast, the submarine Coloumbo volcano is characterized Figure 1.…”