Frequently asked questions about Etna
What is the relationship between Etna and the earthquakes of the region?

The following is a question (from a student in Israel) regarding this subject, and my answer (with a few additions) to this question. More detailed explanation is given below.

Q: "Is there any connection between the occurrence of earthquakes and the activity of Etna?"

A: "Yes, sometimes. There are tectonic earthquakes (...) which occur on faults, similar to the San Andreas in California and, I think, some faults that you have in your country and nearby. These are the strongest earthquakes which can be devastating (most recently in 1693 when Catania was totally destroyed). They are not related to the volcanic activity. Volcanic earthquakes, due to movements of magma below the surface, occur frequently on Etna..."

Sicily is a seismically very active region. Earthquakes are frequent along two major fault systems that extend from Etna to northeast (Messina-Giardini or Messina-Etna fault system) and southeast (Malta Escarpment fault system), and the most devastating earthquakes of the past centuries had their epicenters there. Such earthquakes may exceed a magnitude of 7 (as in the cases of 1169, 1693 and 1908) and are extremely destructive due to the widespread lack of earthquake-proof constructions. The epicenters of these events lie at a distance of about 80 km from Etna in both directions, too far to be directly connected to the activity of the volcano.

There are also many smaller (though at times destructive) earthquakes that originate at faults cutting the eastern, northeastern and southeastern sectors of Etna. These are known as "Etnean earthquakes", but until now no evidence has been found for a direct correlation with the eruptive activity. They are rather envisaged to be the result of movements in a sector of the volcano that is considered "mobile", which is confined between the Pernicana fault on the NE side and the Mascalucia or the Ragalna fault on the S side of Etna. These faults are what geologists call "strike-slip faults" because movement along them is essentially horizontal. Many normal faults that crisscross the "mobile" E sector of Etna are seismically active and thus produce frequent earthquakes; since the hypocenters (the zones at depth where earthquakes originate) are close to the surface, they can be locally devastating although they are never as powerful as the earthquakes along the large fault systems of eastern Sicily. The faults themselves form a spectacular "step"-shaped morphology that gives the E flank of Etna its peculiar character; these steep fault scarps are called by the local people "timpe" (sing. "timpa"). While seismic activity at the "timpe" does not appear to be correlated with visible eruptive processes on the volcano, it is likely that it is to some degree influenced by magma movements deep within the volcanic edifice.

Then there are truly volcanic earthquakes which are caused by the uprise of magma through fissures in the flanks of the volcano. These occurred in spectacular quantities during the days before the July-August 2001 eruption and were one of the clearest indicators of the imminent eruption. Volcanic earthquakes are generally too small to provoke significant damage (the destruction of Nicolosi by pre-eruption seismicity in 1669 is among the few exceptions, but this was due to the location of hypocenters at shallow depth immediately below the village), but they are often felt by nearby residents.

Next Question: When was Catania last affected by an eruption of Etna?

Copyright © Boris Behncke, "Italy's Volcanoes: The Cradle of Volcanology"