The 24 August 2016 earthquake in central Italy

08.26.2016
A severe earthquake occurred on 24 August 2016 in central Italy, between the towns of Norcia and Amatrice. The BRGM reports on the event.

An magnitude 6.2 earthquake occurred on Wednesday 24 August 2016 at 3:36 a.m. local time (1:36 GMT) in central Italy, half way between the towns of Norcia (15 km to the north-west) and Amatrice (about 10 km to the south-east), some 40 km north-west of Aquila and 110 km north-east of Rome. It was followed by numerous aftershocks.

This earthquake was fairly shallow, with an epicentre located some 4km down according to INGV and CSEM estimations. It was sensed more than 200 km from the epicentre and caused damage (IV intensity and more) within a radius of 30 km. The final toll stood at 247 victims according to Italy's civil protection authority. 

Epicentre and aftershocks

Map of the local geological context showing the location of the epicentre of the 24 August 2016 earthquake (after Gori et al, 2014).

The locations, magnitudes and depths of the vent were estimated as follows by the different agencies:

INGV: 42.70N 13.24E; depth 4km ; M 6.0

CSEM: 42.71N 13.22E; depth 4 km  Mw 6.2

USGS: 42.714N 13.172E; depth 10 km; M 6.2

The above map shows the INGV location together with faults and past earthquakes in the region.

The earthquake was followed by numerous aftershocks (Fig. 2) along a NW-SE axis over some 30 km. From 01:36 GMT to 04:06 GMT, there were 5 aftershocks of magnitude 4.5 and more, with the strongest measured at magnitude 5.5 at 02:33 GMT. Two more severe aftershocks occurred at 01:50 (M4.9) and 03:17 on 25 August (M4.6).

Map of the aftershocks (situation on 25/08/2016 at 08:00 local time)

The regional context

The earthquake occurred in the central Apennines along a system of normal, active surface faults (cf. Figure 1). The context is similar to that of the 2009 Aquila earthquake, which occurred about 40 km to the south, and corresponds to an expansion zone of the Apennine Range.

As shown in Figure 1, this region has experienced a number of major and very destructive earthquakes over the last century: most recently in Aquila (April 2009, M6.3, over 300 fatalities), but also the Umbria-Marches sequence in 1997 (M6.0, 11 fatalities) and the Avezzano earthquake of January 1916 (M6.7, tens of thousands of victims).

The main epicentre of the 24 August 2016 earthquake was between the Norcia fault (NF in Figure 1) and the Laga fault (LMF in Figure 1). This is the same epicentral zone as that of a major earthquake (Lat 42.71, Long 13.07, magnitude Mw= 7), with an epicentral intensity of XI, which occurred on 14 January 1703 and caused catastrophic damage.

Estimating the intensity of shocks

A shakemap is a tool that calculates an intensity map from data recorded by the seismic surveillance network. In the first hours after an earthquake, a shakemap can only give an estimation rather than a true map of the observed intensity of the event. It nevertheless produces an initial earthquake report within a very short time.

Two shakemaps are available for this event, from Italy's INGV and the North American USGS.

An estimation can be made from these shakemaps of the radius of intensity within which damage can be expected (above VI), which varies from 20 to 40 km around the epicentre.

USGS shakemap of the main shockwave.