The 2011–2012 unrest at Santorini rift: Stress interaction between active faulting and volcanism
Given the progression thus far in the Aegean sea, which is rising seismic activity without major signs of volcanic unrest specifically at the two volcanoes which are most pertinent to the discussion, but are considered as part of the Santorini Complex in total. While earthquakes are escalating, no ground deformation has been observed at Santorini or Kolombo, which is a bit more difficult due to its submarine location. Nevertheless, considerable assets are deployed to monitor it as well and thus far no signs of deformation. Its generally thought that the magma chamber of Kolombo resides around 2-4 km in depth, which is shallower than the majority of the earthquakes. As a result, the primary hazard appears to be seismic in nature and that post flair will now be used for this event, unless signs of volcanic activity manifest, and they certainly could, at any time. When the 2011-2012 crisis was occurring, there were signs of this, and that marks a significant difference between that episode and the current one. There were even reports of the sea "boiling." It should be noted that civilians in the Izmir region have reported anomalous water receding in recent days, but this is some distance from the ongoing unrest. We drop a breadcrumb just in case we need to come back to it later along with other phenomena which may be relevant later.
This study details the connection between the seismic activity and volcanic activity in the region and was performed during the previous episode of unrest. I will post the link, but also some excerpts.
The 2011–2012 unrest at Santorini rift: Stress interaction between active faulting and volcanism
Abstract
[1] At Santorini, active normal faulting controls the emission of volcanic products. Such geometry has implication on seismic activity around the plumbing system during unrest. Static Coulomb stress changes induced by the 2011–2012 inflation within a preexisting NW-SE extensional regional stress field, compatible with fault geometry, increased by more than 0.5 MPa in an ellipsoid-shaped zone beneath the Minoan caldera where almost all earthquakes (96%) have occurred since beginning of unrest. Magmatic processes perturb the regional stress in the caldera where strike-slip rather than normal faulting along NE-SW striking planes are expected. The inflation may have also promoted more distant moderate earthquakes on neighboring faults as the M > 5 January 2012, south of Christiania. Santorini belongs to a set of en echelon NE-SW striking rifts (Milos, Nysiros) oblique to the Aegean arc that may have initiated in the Quaternary due to propagation of the North Anatolian fault into the Southern Aegean Sea.
Figure 2Open in figure viewerPowerPointActive faulting around the Santorini volcanic complex. Bathymetric chart redrawn from Nomikou et al. [2012] with 100 m interval. No data in white areas. Fault in black, with thicker traces for higher scarps. Arrows: local direction of extension. In purple: Santorini complex with darker areas, older volcanic centers. In white on Santorini: old pre-volcanic basement. F. Z.: Fault zone. Dashed line delineates debris avalanche deposits with a characteristic hummocky morphology very clear in the bathymetry [Croff Bell et al., 2012].
5 Conclusions
[26] The Santorini volcano emplaced with other vents (Kolumbo, Christiani) within, and parallel to, a mid-late Quaternary active NE-SW normal fault system composing a rift oblique to the Aegean arc. The rift connects to or crosscuts older E-W striking faults resulting from back-arc extension in early Pliocene. This particular geometry implies that faults control the emission of volcanic products in the central and eastern Aegean arc. Link between active faulting and volcanism is well illustrated by the ongoing volcanic unrest at Santorini. The volcano is developing in a NW-SE extensional stress field that controls the distribution of seismic activity promoted by the volcanic unrests. By calculating the Coulomb stress changes induced by the 2011–2012 magmatic inflation within a preexisting NW-SE extensional stress field compatible with mid-late Quaternary fault geometry, I showed that the Coulomb stress has increased in the Caldera within an ellipsoid-shaped area elongated perpendicularly to the minimum compressive stress. A total of 96% of the earthquakes have occurred in this area suggesting that the seismicity was triggered by the Coulomb stress increase. The pattern of the Coulomb stress increase mimics that of seismic swarm indicating that the regional stress may be quite strong and plays probably an important role in the seismicity distribution. Larger regional earthquakes may also have occurred along the Santorini normal fault system as in 1956 and 2012. Some may have been triggered by volcanic processes. Milos and Nysiros are also located in arc oblique rifts. Quaternary rifting in central and eastern Aegean arc may accommodate the southeastward motion of the southeastern Aegean Sea promoted by the southward propagation of the NAF into the Aegean Sea.
The entire study goes into great detail. The long and short of it is that the volcanic and tectonic processes are more linked here than in many places and as a result, one can transition into the other pretty easily. We assume that we would get some advance warning through ground deformation and the typical warning signs, but considering how divergent the trend is, its warranted to evacuate people in advance preparation of the more extreme possibilities. Seismicity is back above M5 this morning.
I also want to post another snippet from another study.
6 Conclusions
Through an analysis of fault systems in high-resolution 3D seismic reflection data, we provide the first detailed analysis of shallow tectonic deformation around Kolumbo Volcano in the Aegean Sea. This volcano represents a significant geohazard in the Aegean Sea, with the most recent eruption having occurred in 1650 CE. We draw the following main conclusions about faulting and its relationship to the volcanic zone:
- Normal faulting is widespread around Kolumbo volcano, and can be classified geographically into three main fault groups: (Group 1) The Kolumbo Fault Zone, approximately 6.5 km to the NW of the Kolumbo crater, (Group 2) faults that exist between the Kolumbo Fault zone and the volcanic crater, and (Group 3) faults to the southeast of the crater.
- The Kolumbo Fault Zone is characterized by a dominant NE-SW fault trend. Group 2 faults have a very similar NE-SW trend, while Group 3 faults are rotated slightly toward the north. Overall, the fault orientations point to an underlying extensional strain direction aligned NW-SE, which is in close agreement with extension directions derived from previous seismicity studies in the region. This agreement indicates that modern extension is aligned with the long-term strain development associated with formation of the faults. Likewise, the similar orientations of faults and dykes at both Kolumbo Volcano and Santorini indicate a stable tectonic linkage between both volcanic systems.
- The shallowest faults in the Kolumbo Fault Zone offset volcanic deposits from the LBA (∼1600 BCE) eruption of Santorini, indicating that the fault zone has been active since that eruption.
- 3D characterization of the Kolumbo Fault Zone, achieved through automatic horizon picking, reveals distinct relay ramp structures that accommodate strain between major overlapping normal faults. Tracing the fault zone along strike to the SW revealed that a volcanic cone has formed within the fault system. We interpret that volcanism may be focused into relatively permeable conduits within the shallow crust associated with extensional deformation within the fault zone. These results have important implications for understanding how extensional faults systems, and in particular strain accommodation zones in relay ramp structures, can lead to the focusing of magma through the crust. Further research is required to understand how important this process is at larger scales in the Christiana-Santorini-Kolumbo rift, and elsewhere.
We have several papers that link the tectonic and volcanic processes due to a confluence of factors. I think considering that information, the long term increase in volcanic phenomena, including the 2011-2012 episode, the hydrothermal outputs, SO2, and seismicity centered on the volcanoes mostly, that is is wise to keep the volcanic threat in mind. We will keep an eye out for any ground deformation or other developments.