The two powerful earthquakes that hit central Italy on Oct. 26 are considered aftershocks of the deadly Aug. 24, M6.2 earthquake that occurred near Teramo, which about 50 miles south-southeast of the latest temblors, according to Boston-based catastrophe modeling firm AIR Worldwide.
A shallow M5.5 earthquake shook central Italy at 7:10 p.m. local time, south-southwest of Visso, followed at 9:18 p.m. local time by a shallow and more intense M6.1 quake, which struck just north of Visso, said AIR Worldwide.
Damage to buildings and infrastructure has been reported, although less than would be expected from shocks of these magnitudes due to the widespread destruction from the August earthquake, the company said.
Wednesday’s events were deeper aftershocks of the August earthquake, “with focal depths of 10.0 km (6.2 miles), compared to the 4.4 km (2.7 mile) focal depth of the deadly August rupture. The largest instrumentally recorded rupture in the region was a devastating 1915 M6.7 earthquake, which resulted in approximately 32,000 deaths,” said Dr. Claire Pontbriand, senior scientist at AIR Worldwide.
“Numerous aftershocks have been felt since the initial quakes, including an M4.9 quake, which occurred about two hours after the M6.1 quake. No injuries or deaths have been reported — many people in the region went outside after the initial shock — although darkness and rain hampered early response activities,” added Pontbriand.
The majority of buildings in Italy are constructed with unreinforced masonry, reinforced masonry, or reinforced concrete construction, AIR Worldwide said, noting that most structures were built before the introduction of comprehensive seismic building codes and modern construction technology.
As a result, the company added, “the risk of collapse during an earthquake for those erected prior to 1980 is very high.”
In 1996 provisions were introduced to limit excessive building flexibility, which can cause damage to the nonstructural elements of a building during low-to-medium intensity earthquakes, AIR continued.
The pre-1996 seismic codes usually have deficiencies that result in a high risk of collapse during powerful earthquakes and high risk of nonstructural damage during weaker ones, the company said. “The seismic codes in Italy did not change significantly until 2003, when an update put most of the areas that are affected by these earthquakes in the high seismic zone, where strict design is required; thus, buildings built after 2004 in these areas are expected to be less vulnerable.”
Source: AIR Worldwide
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