By David Jacobson, Temblor

See earthquakes in Lesbos

At 3:28 p.m. local time, a M=6.3 earthquake struck just south of the Greek Island of Lesbos (Lesvos), near the international border with Turkey. So far, there have been 33 aftershocks in close proximity to the mainshock, with the largest being a M=4.9. According to the USGS, severe shaking was felt close to the epicenter, and there are numerous reports of damage on Lesbos, a popular tourist hotspot (see video below). Based on the USGS PAGER system, fatalities are unlikely, while economic losses are estimated to be between $10-100 million.

The Greek island of Lesbos, is home to approximately 87,000 people, making it the most populated in the Eastern Aegean. The tectonic activity in the area is associated with the broader evolution of the Aegean Sea. Along Lesbos’ southern coastline, and extending offshore are several active faults with components of both left-lateral strike-slip and extensional motion. The main faults, which have been added to the Temblor map above are the Polichnitos-Plomari and Aghios Isidoros-Cape Magiras faults. The Polichnitos-Plomari Fault is primarily extensional, though it also has a strike-slip component. Activity along it is related to theremal activity from the nearby Polichnitos geothermal field. The Aghios Isidoros-Cape Magiras Fault on the other hand is primarily extensional with a small amount of strike-slip motion. While these faults are close to the epicenter of today’s quake, based on the strike of the event, which was almost purely extensional it likely occurred on an additional, unmapped structure within the Aegean Sea.

Due to the quake’s moderate magnitude, and shallow (9 km) depth, shaking was widely felt across the region, including in Athens, the Turkish Cities of Izmir and Istanbul, and Sofia, the capital of Bulgaria. Based on the USGS Shakemap and felt reports from the European-Mediterranean Seismological Centre, over 50 million people were exposed to some degree of shaking. However, damage appears to be isolated to the island of Lesbos, where building facades have come down, and 10 people have been injured.

The video below shows damage sustained on Lesbos in today’s M=6.3 earthquake



In addition to the M=6.3 mainshock, and the 33 aftershocks in close proximity, there also may have been two remote, dynamically-triggered aftershocks, up to 75 km away. One of these, a M=3.3 10 minutes after the mainshock was less than 15 km from Izmir. While it is possible that these quakes are incorrectly located, it is possible that they are remote aftershocks.

Based on the Global Earthquake Activity Rate (GEAR) model, which is available in Temblor, today’s M=6.3 earthquake should not be considered surprising. This model, which uses global strain rates and seismicity since 1977 forecasts what the likely earthquake magnitude is in your lifetime anywhere on earth. From the Temblor map below, one can see that in the location of today’s quake, a M=6.5+ is possible. Therefore, while this earthquake was damaging and caused injuries, a larger quake in the region could happen, resulting in more extreme damage.

References

European-Mediterranean Seismological Centre (EMSC)

Chatzipetros, A., Kiratzi, A., Sboras, S., Zouros, N., Pavlides, S., Active Faulting in the nore-eastern Aegean Sea Islands, Tectonophysics 597-598 (2013) 106-122

USGS