This current earthquake sequence, which nominally began back in August, has featured 44 tremors that have registered as 4.0M or larger. The United States Geological Survey (USGS) has suggested that the August event may have loosened up faults in the region, allowing them to slip more easily than before.
Many assumed that the 6.2M August quake southeast of Norcia was likely to be the most powerful in the sequence. After all, such a huge event would likely have unleashed plenty of built up stress in the region, meaning there was little left “stored up” in the fault networks.
However, this weekend’s event, which hit just north of Norcia, registered as a 6.6M. This suggests that in this case, an independent fault section – one that had been building up stress and had remained unruptured for some time – gave way. The hundreds of aftershocks the region has experienced since suggests that the nearby faults have all loosened up somewhat as a result.
“We can expect aftershocks to continue for weeks and possibly months,” the USGS noted in a statement. “We cannot rule out the possibility of similar sized or larger events, though the probability of a larger event is low.”
The August event occurred at a depth of 4.4 kilometers (2.7 miles), while the October event originated at a depth of 10 kilometers (6.2 miles). Their relative shallowness meant that the surface-level shaking was particularly intense both times.
Any future extensional earthquakes will likely be at similar depths – and, sadly, will likely be no less destructive. So don’t expect these tremors to fall out of the news cycle any time soon.
The extension of the Tyrrhenian Sea, pictured here, is to blame. EugeniaSt/Shutterstock