Why the Italian quake matters for New Zealand

In the wake of the Christchurch Earthquake, former Canterbury geologist Dr Mark Quigley was the face of science, explaining the geological processes that caused it. Now based at the University of Melbourne, Quigley discusses the quake that has just shaken Italy and its relevance to New Zealand.

Today's magnitude 6.1 Norcia 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 one metre.

A surface rupture or other form of surface deformation is possible.

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.

A survivor looks at the collapsed buildings of the town of Pescara del Tronto, Italy. Photo / AP

Roughly 10,000 people were killed in Norica, Montereale, L'Aquila and the encompassing Appenine region in three magnitude 6.2 to 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 to 20 seconds.

Another 230,000 people or more would have experienced very strong shaking.

A man is carried out on a stretcher as a collapsed building is seen in the background. Photo / AP

Things like site effects - the local behaviour of different types of foundation materials to shaking, for example soils vs gravels vs rocks - will be important in influencing the patterns and severity of shaking-induced damage.

The estimated damage will almost inevitably exceed US$100m and may exceed US$1b.

Distinctly from Christchurch, where the region is being squeezed between the Pacific Ocean and the Southern Alps, this part of Italy is experiencing crustal extension; eastern central Italy is moving to the north-east 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, being almost always magnitude 6.8 to 7.

But because the earthquakes are shallow and structurally complex, like the 2011 Christchurch earthquake, 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.

A man is pulled out of the rubble. Photo / AP

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.

Italy has a rich record of seismologic and paleoseismologic research.

But the knowledge of the hazard has not always translated well into measures that directly reduce 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 due largely to financial constraints.

Both the 2016 Norcia earthquake, and the 2009 L'Aquila earthquake, highlight just how important it is to translate hazard assessments into improving the resilience of infrastructure to strong shaking.

The future focus in this region should remain on the science-engineering-policy interface; although this was one of the strongest aspects of the Christchurch earthquake recovery process, it has often proven to be the most challenging linkages in other settings around the globe.