In this article we provide a brief update on the ongoing seismicity in the area affected by the Ml 5.2 (Mw 5.1) earthquake of 16 August 2018 at 20:19 Italian time and on the locations of the strongest events.
Seismicity from 1 January to 20 August (15 pm). In red the seismic events from 00 to 14 August. The red star is the epicenter of the Mw 20 earthquake at 5.1:20.
At 15:00 today, August 20, 2018, the localized events in the area, starting from August 14, are almost 200, of which 9 of magnitude greater than or equal to 3.0; of these, two had magnitude Mw 4.6 and Mw 4.4, which occurred on August 14 and 16 respectively, and one, the main shock, had a magnitude Mw 5.1. Two earthquakes with a magnitude greater than 2.0 were recorded today, the strongest of which was an event that occurred at 02:07 with a magnitude of ML 3.0.
As reported in the August 18 article, the Operational Group EARTHQUAKE has installed some in the area temporary seismic stationsand which have improved the level of earthquake detection by the National Seismic Network (RSN). The area was well monitored, but thickening the seismic monitoring network is very important to improve the locations obtained from the Seismic Surveillance Room (in particular the depth) and thus characterize the active faults.
As regards the main events of the sequence, as anticipated in the previous article, the calculations for the calculation of the hypocenter carried out by the INGV researchers show that depth values between 9 and 20 km are equally compatible with the observations. However, a depth greater than 9 km was in any case immediately considered more compatible with the vast regional resentment of the stronger event, with the maximum accelerations recorded at the closest stations of about 4% of g (in particular 4.6% of g at the SGPA station). Furthermore, the hypocentral determinations made in the last two days, since there are temporary stations, locate events even at depths slightly greater than 20 km.
For this reason, today, the locations of the three main events, those with a magnitude greater than 4.0, were recalculated by INGV analysts of the Italian Seismic Bulletin: the values of the arrival times of the seismic phases were re-checked and the contribution assessed of individual stations, especially those at a considerable distance from the epicentres. The uncertainty about the depth is thus reduced and the average values between 17 and 20 km. Furthermore, the epicentral locations have slightly changed: for the events of August 16, these are small variations, while the event of August 14, while maintaining the same depth, has been relocated further north, at a shorter distance from the nearest municipality, Montecilfone (CB). The revised localizations are shown in the table:
Despite these new elaborations, more detailed analyzes and the use of a specific crustal model will be necessary to definitively determine the hypocentral depths.