An earthquake measuring ML 4.0 (Mw 3.9) occurred this morning at 06:25 Italian time (23 April 2017 at 04:25 UTC) in the province of Foggia, in the Gargano promontory. The epicenter was located by the INGV National Seismic Network at a depth of about 22 km.
The seismicity from 1 January 2017 (in blue) and that of the last three days (in yellow) in the Gargano area. The yellow epicenter highlighted with a red circle is that of this morning (06.25 Italian time) of magnitude Ml 4.0 (Mw 3.9).
At the moment (11:00 am) no other tremors have been located in the area. On April 18 and 21, two seismic events of magnitude 2.2 and 2.1, respectively, occurred about 10 km west of today's event.
The municipalities within 20 km from the epicenter are as follows (the columns after the names respectively indicate the province, the distance from the epicenter in km, the inhabitants):
The seismicity map of the last 10 years reveals the presence of seismic activity in the area of the Gargano promontory. The most significant events in this period in that area are two: the one located south-east of today's one, which occurred on May 29, 2006 with a magnitude Mw 4.5 and the one located north-east on March 19, 2008 with a magnitude Mw 3.9 .
Seismic activity since 1 January 2006 (in blue) and that of the last 24 hours (in orange) in the Gargano area. The yellow epicenter highlighted with a red circle is that of this morning (06.25 Italian time) of magnitude Ml 4.0 (Mw 3.9).
The Parametric Catalog of Italian Earthquakes (2015 version) shows 4 events of magnitude equal to or greater than 6.0 in the Gargano area with epicentral location, based on historical information, in a strip slightly south of the location of today's event. The most important are the events of the 600s, in particular the two of 1627, in the westernmost part of the promontory with a magnitude of 6.7 and 6.0 (respectively on 30 July and 7 August), the one of 1646 with a magnitude of 6.7 located in the center of the promontory and the event of 1657 (magnitude 6.0) located near the event of 1627. The historical earthquake closest to today's event is that of 1889 with a magnitude of 5.5.
Historical seismicity in the Gargano area. The yellow epicenter highlighted with a red circle is that of this morning (06.25 Italian time) of magnitude Ml 4.0 (Mw 3.9).
The calculation of the moment tensor gave an almost pure focal strike-slip mechanism with right movement in the ESE-ONO plane (left movement in the conjugate plane) and a value of the moment magnitude Mw equal to 3.9. The movement deduced from the focal solution is congruent with what is known from the literature and from the tensor moments available for the area.
According to the questionnaires that have arrived so far on the site http://www.haisentitoilterremoto.it/, this morning's earthquake was felt throughout the Gargano area, up to Foggia and Lucera. Below is the map (updated at 10:33) with the distribution of seismic impact expressed in MCS scale (Mercalli-Cancani-Sieberg).
Map of seismic effect in MCS scale (Mercalli-Cancani-Sieberg) showing the distribution of the effects of the earthquake on the territory as reconstructed from the online questionnaires. The map contains a legend (on the right). The purple star indicates the epicenter of the earthquake, the colored circles refer to the intensities associated with each municipality. The caption above shows the characteristics of the earthquake: date, magnitude (ML), depth (Prof) and local time. The number of questionnaires processed to obtain the map itself is also indicated.
For more information on this event: link