Tectonic Summary

The August 24, 2016 M 6.2 earthquake southeast of Norcia, Italy, occurred as the result of shallow normal faulting on a NW-SE oriented fault in the Central Apennines. The Apennines is a mountain range that runs from the Gulf of Taranto in the south to the southern edge of the Po basin in northern Italy. Geologically, the Apennines is largely an accretionary wedge formed as a consequence of subduction. This region is tectonically and geologically complex, involving both subduction of the Adria micro-plate beneath the Apennines from east to west, continental collision between the Eurasia and Africa plates building the Alpine mountain belt further to the north and the opening of the Tyrrhenian basin to the west. The evolution of this system has caused the expression of all different tectonic styles acting at the same time in a broad region surrounding Italy and the central Mediterranean. The August 24, 2016 normal faulting earthquake is an expression of the east-west extensional tectonics that now dominate along the Apennine belt, primarily a response to the Tyrrhenian basin opening faster than the compression between the Eurasia and Africa plates. At the location of the earthquake, the Eurasia plate moves towards the northeast with respect to Africa at a rate of approximately 24 mm/yr.

The central Apennine region has experienced several significant earthquakes in recorded history. In September 1997, a Mw 6.0 earthquake 50 km north-northwest of the August 24, 2016 event killed 11, injured over 100 and destroyed approximately 80,000 homes in the Marche and Umbria regions. This 1997 event was part of a series of earthquakes known as the Umbria-Marche seismic sequence, which included eight events of magnitude greater than M5.0 in a two-month period between September and November of that year, including the events that substantially damaged the Basilica of St Francis in Assisi. In April 2009, a Mw 6.3 earthquake 45 km to the south-southeast of the August 24, 2016 event, near the town of L’Aquila, killed at least 295, injured over 1,000 and left 55,000 or more homeless. The L’Aquila earthquake resulted in significant landsliding in the local area, and was also followed by a vigorous aftershock sequence, including 5 other events of M 5.0 or larger. The largest instrumentally recorded earthquake within 100 km of the 2016 event was the January 13, 1915 M6.7 earthquake, which occurred 68 km to the south-southwest near Avezzano. The 1915 earthquake killed approximately 32,000 people. The preliminary location of the 2016 earthquake appears to be in a gap between the aftershock sequences of the 1997 and 2009 events.