Insight on fault segmentation, linkage and hazard from the 2016 Mw6.2 Amatrice earthquake (central Italy)

We investigate the 2016 Mw6.2 Amatrice earthquake (central Italy) with a combination of bodywave seismology, field measurements and satellite geodesy, and show that the earthquake ruptured across two normal faults that had previously been identified as separate structures.
Our coseismic source model, obtained from GPS and InSAR data, shows slip in two major patches, taking place over a total length of ~20 km, and mainly constrained to shallow (2-7 km) depths. Our model shows that the highest slip was focussed on the unknown linking section between the mapped Laga and Vettore faults. Our model predicts primary surface rupture to be present only on the Vettore fault, in agreement with our field observations.
Our seismological model has a simple source-time function, implying that within the resolution of the data, the rupture proceeded without pause across the linking section between the Vettore and Laga faults.
Both faults were previously identified as active, but field mapping, remote sensing data, geomorphology, and Holocene slip rates had all been used to support the idea that the faults were separate structures. Each had been thought capable of producing an earthquake with MW<6.5.
However, our study suggests that these faults appear to be better linked at depth than previously thought, allowing through-going rupture. Although the Amatrice earthquake did not rupture the full extent of the Laga and Vettore faults, we suggest that if such a scenario did happen with 1 m average slip, the two faults are capable of producing a MW7.1 earthquake. This type of fault behaviour has precedent in Italy; the destructive 1980 MW6.9 Irpinia earthquake in southern Italy was composed of multiple MW6.2-6.5 sub-events on four separate segments. Each of the MW6.7-7 largest known events in central Italy; the 1703 Norcia and L’Aquila earthquakes and the 1915 Avezzano earthquake, are also thought to have involved multi-fault rupture.