EXPERT COMMENT: Giulio Di Toro on the recent Italian earthquake
Professor Giulio Di Toro is the Geology Chair at The University of Manchester's School of Earth and Environmental Sciences, and was conducting research in central Italy this week when the earthquake struck. Here, he writes about why it was so destructive, and the research being done at Manchester into understanding the causes of such quakes in the country.
The magnitude 6.0 earthquake that hit the Central Apennines in the early hours of Wednesday is quite typical in this part of Italy. In fact, at least four strong earthquakes have hit the villages of Amatrice, Accumuli and Norcia in the last few centuries: in 1639 (estimated magnitude 6.2), 1646 (estimated magnitude 5.9), 1703 (estimated magnitude 6.9) and in 1979 (mainly the area of Norcia, magnitude 5.9).
Unfortunately, earthquakes of moderate to strong magnitude in the Central and Northern Apennines are characterised by relatively long seismic sequences that may last for months, or even years. These also include strong aftershocks (we cannot exclude at the time of writing that Wednesday’s shock could be a foreshock of a larger earthquake), plus hundreds to thousands of smaller ones (magnitude 2.0-4.0) that can be felt by the population. The largest aftershock so far occurred an hour after the initial quake, and was 5.3 in magnitude.
At the time of writing there have been 247 casualties, and the main shock at 3.36 am was felt in most of Central and North-East Italy - an area of about 100,000 square kilometres.
The large number of fatalities for an earthquake of this magnitude, which would produce almost none in countries like Chile or Japan, is due to the poor resilience of the (albeit beautiful) buildings of the Italian medieval villages - Amatrice was included in 2015 in the list of Italy’s most beautiful villages - and a lack of adherence to construction codes.
Hospitals, police stations, schools and barracks in Amatrice and Accumuli completely collapsed during the earthquake - with the exception of a gym that is now being used to house displaced residents – whereas the village of Norcia, which was rebuilt adhering to the construction codes after the 1979 earthquake, suffered little damage and no casualties despite being located in the epicentral area.
Earthquakes are the result of ruptures that spread along geological structures called faults. This particular quake happened at a depth of around 5-9km (more accurate hypocentral depth estimates will be released in the next days), and spread for about 20-25km along the fault.
These earthquakes are due to the collision between the African and European plates, which results in the counter-clockwise rotation of the Italian peninsula and the 5mm annual extension of the mountains in the Northern and Central Apennines. This leads to a series of sub-parallel active normal faults striking about northwest-southeast and dipping towards the southwest, including those that ruptured in this case.
To understand the mechanics of the earthquakes that hit Central Italy (including 2009’s magnitude 6.3 L'Aquila earthquake, which caused 309 casualties), the School of Earth and Environmental Sciences at The University of Manchester is performing a multidisciplinary study which includes field investigations of seismogenic faults now exposed at the Earth's surface, experimental studies to reproduce in the laboratory seismic deformation conditions and microstructural studies on experimentally deformed and natural fault rocks to understand the deformation mechanisms that control how the earthquake engine works.
These studies are funded by the European Research Council’s NOFEAR project, in collaboration with the Istituto Nazionale di Geofisica e Vulcanologia in Rome, the Dipartimento di Geoscienze at the University of Padova and the Department of Earth Sciences at the University of Durham.
The field studies at the School of Earth and Environmental Sciences involve Ph.D. Michele Fondriest, Ph.D. Francois Passelegue and B.Sci. Harry Leah. In particular, in his Master’s thesis in Geology, Harry is focusing on the structure of an exposed fault which is probably quite similar to those that are ruptured in this quake – in fact, Gran Sasso-Campo Imperatore, the field area he is investigating, is located only 25-30km away. This area was selected because of the excellent exposures, which allow us to conduct detailed field studies (from the km to the mm-scale) focusing on the geometry of these seismogenic faults.