By John Kerr 24/08/2016


The dust is still settling in the wake of the tragic 6.1 earthquake that struck near Norcia in central Italy. Latest reports indicate that at least 38 people died in the quake which has caused widespread damage in Norcia and nearby towns [Update: the death toll is now estimated to be 159 lives lost].

ShakeMap Intensity image
ShakeMap Intensity image from the US Geological Service.

Associate Professor Mark Quigley from the School of Earth Sciences at the University of Melbourne was an earthquake researcher at the University of Canterbury during the Canterbury quakes in 2010 and 2011. He provided the following commentary to the Australian Science Media Centre (via Scimex.org).

“The moment magnitude 6.2 earthquake occurred at 3:36 am local time with an epicentre approximately 10km SE of Norcia, Italy. The size of the fault that ruptured is probably around 10 x 10 km. The maximum amount of slip on the fault will probably be about 1 meter. A surface rupture or other form of surface deformation is possible. Strong aftershocks will affect this region over the coming days to months. The largest aftershock from the 2009 L’Aquila earthquake was a magnitude 5.5. In some cases these aftershocks can cause more damage than the preceding larger earthquake. For every magnitude 5 aftershock, 10 magnitude 4s are expected. There will be thousands of small aftershocks throughout the region from this event, but most will go unfelt.

“This earthquake is no surprise. This is one of the most seismically active parts of Italy as clearly identified in many seismic hazard maps. During the past seven centuries, Norcia has been hit by six earthquakes that have caused very strong to severe shaking. Roughly 10,000 people were killed in Norica, Montereale, L’Aquila and the encompassing Appenine region in three magnitude 6.2-6.7 earthquakes in 1703. Parts of Norcia were subsequently built upon the surface rupture created in the 1703 earthquake. Another earthquake in 1997 caused 11 fatalities. In this most recent event, an estimated 13,000 people would have experienced severe ground shaking that would have persisted for probably 10-20 seconds. The estimated damage will almost inevitably exceed $100M USD, and may exceed $1B.

“This part of Italy is experiencing crustal extension; eastern central Italy is moving to the NE relative to Rome. As a result, this region experiences normal faulting earthquakes as the land is torn apart. The fault systems are short and structurally complex, so the earthquakes are not overly large by global standards (almost always < magnitude 6.8 to 7). But because the earthquakes are shallow and structurally complex, and because many of the local towns and cities contain vulnerable buildings, strong shaking from these earthquakes has the potential to inflict major damage and loss of life in urban areas. Furthermore, this region seems to be particularly prone to earthquake clustering, whereby periods of relative quiescence are interrupted by several strong earthquakes over timescales lasting from weeks to decades.

“My experience in the region is that there is excellent and continuously improving scientific information about the hazard here. But the knowledge of the hazard has not always translated well into measures that directly reduce future economic loss and fatalities in earthquakes. Numerous vulnerable buildings remain, and the recovery process is commonly plagued by long disruptions and inadequate government funding to recover rapidly. For example, when I visited L’Aquila in 2013, large parts of the city were still cordoned off, numerous buildings had not been repaired or demolished, and recovery had stagnated.

“Both the 2009 L’Aquila earthquake, and this most recent earthquake, highlight just how important it is to translate hazard assessments into improving the resilience of infrastructure to strong shaking. The focus should remain on the science-engineering-policy interface; this is often the most challenging linkage to improve upon globally.”

Featured image: GieffeCi via Titter.