Quake and Shake: Santorini’s Earthquake Crisis

Santorini, Greece is one of the most picturesque vacation destinations in the world. With its classic white and blue buildings, traditional cobblestone streets, and a tropical sunset overlooking the Aegean, it’s no wonder Santorini was the chosen cinematic location for many famous movies including Mamma Mia and The Sisterhood of the Traveling Pants. However, due to its volcanic history and tectonic location within the Aegean, it is constantly at risk for destructive earthquakes.

Fira, Santorini after sunset June 4th, 2019

Greece is the 6th most seismically active (or earthquake prone) country in the world. With a subduction zone at the Hellenic trench forcing the African plate under the Aegean plate as well as other subsequent faults throughout the region, it is common to have earthquakes related to both these moving plates and volcanism along the oblique slip faults (see Emily Godin, 2019 for more details on the Aegean tectonic system).

Geography and Fault Systems of Santorini

Santorini is an archipelago (or group) of 5 islands that sit on two active oblique slip faults. The Kolumbo fault is in line with the underwater volcano Kolumbo just northeast of Santorini, and the Kameni fault is below both Palea and Nea Kameni (Fig. 1). These faults can trigger earthquakes through tectonics (movement of plates), or through volcanism as magma finds its way to the surface through space created by these types of faults.

Figure 1: Geographic location of archipelago and active fault locations on Santorini

These oblique slip faults mark the five main volcanic centers in the Aegean Sea. Because the Aegean plate is moving southwest relative to the African plate, these volcanic centers are younger and more seismically and volcanically active further to the East. In the last 50 years, most of the earthquakes throughout the Aegean occurred at the subduction zone and to the east-most volcanic centers (Fig. 2).

Figure 2: Seismicity map of the Aegean Sea showing significant earthquakes over the past 50 years (magnitude 4 or higher). The stars represent the five volcanic centers in the South Aegean Active Volcanic Arc. The red line identifies the subduction zone at the Hellenic Trench. Modified from Dimitriadis et al. (2009)

An earthquake’s magnitude is determined solely by the total amount of energy released by the quake in a scale called Moment Magnitude. Unlike common belief, the intensity of an earthquake cannot be determined by its magnitude alone. The intensity can change due to a number of factors such as the rigidity of a building, the consolidation of earth material underneath, and the distance from the epicenter (origin of where exactly the earthquake occurred). In Santorini’s case, the buildings are mainly brick (a very rigid material) built on top of old volcanic deposits which are very unconsolidated and unstable. Because seismic waves slow down and amplify in unconsolidated material, the island would experience a much higher intensity earthquake with a lower magnitude.

The 2011-2012 Crisis Period

Between January 2011 and May 2012, there was a large increase in earthquakes coming from Nea Kameni and the caldera of Santorini for the first time in 25 years. Because these quakes were low magnitude, growing shallower overtime, and nonstop, the cause was due to an increase in volcanic activity underneath Nea Kameni and not the fault systems directly. For a total of 16 months, the island experienced over 50 earthquakes a day (Fig. 3). This period of unrest is now considered the 2011-2012 Crisis Period.

Figure 3: Recorded earthquakes and their magnitudes between January 2011 and September 2012 and geographic identification of Nea Kameni and the Kameni fault line. Modified from F. Tassi et al. (2013)

The last major earthquake that affected Santorini was the 1956 Amorgos Earthquake. With a magnitude 7.7, this quake occurred close to the island of Amorgos 60 miles northeast and caused massive destruction throughout Santorini. For more information on this event, see Bailey Estes (2019). Though both events occurred along active faults, the Crisis Period was directly caused by volcanism, not the fault systems throughout the Aegean.

By using scientific instruments, seismologists were able to determine the true cause of the frequent quakes. Seismometers on Nea Kameni were able to find the source, depth, and magnitude of the quakes which helped solidify that the cause was truly due to volcanic activity (Fig. 4).

Figure 4: Seismometer station on Nea Kameni. Seismometers record data as seismographs to identify, locate, and measure earthquakes

These earthquakes set off an alarm in the scientific community, but there was no media coverage or publicity during this time. Though these volcanically induced quakes were obviously affecting locals, since the event was not advertised as a “crisis”, business and tourism continued as normal even though the island was constantly shaking.

The Crisis Period was a time of increased volcanic activity and uncertainty throughout the population. Though the Santorini residents are accustomed to living within in the threat of an active volcano and fault system, the fear of a possible eruption from Nea Kameni or a larger earthquake was widespread. Because tourism and business did not stop during this period, the only in-depth knowledge about this event was present in the scientific community. If you choose to travel to an area with an active volcano or nearby fault boundary for vacation, be sure to do some scientific research on the area and formulate a plan in case an earthquake occurs.

We cannot stop natural disasters, but we can arm ourselves with knowledge; so many lives wouldn’t have to be lost if there was enough disaster preparedness.

Petra Nemcova

References

F. Tassi, O. Vaselli, C. B. Papazachos, L. Giannini, G. Chiodini, G. E. Vougioukalakis, E. Karagianni, D.Vamvakaris, D. Panagiotopoulos, 2013, Geochemical and isotopic changes in the fumarolic and submerged gas discharges during the 20122-2012 unrest at Santorini caldera (Greece): Bull Volcanol, v. 711.

I. Dimitriadis, E. Karagianni, D. Panagiotopoulos, C. Papazachos, P. Hatzidimitrious, M. Bohnhoff, M. Rische, T. Meier, 2009, Seismicity and active tectonics at Columbo Reef (Aegean Sea, Greece): Monitoring an active volcano at Santorini Volcanic Center using a temporary seismic network: Elsevier, v. 465, p. 136-149.

Neoskosmos, 2015, Santorini Volcano Back in Dormant State: https://neoskosmos.com/en/30004/santorini-volcano-back-in-dormant-state/ (accessed June 2019).

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