English version

The seismometric Friuli-Venezia Giulia network of the Seismological Research Centre (CRS), a Department of the National Institute of Oceanography and Geophysics (OGS), has recorded an earthquake on June 12, 2004 at 13:04 GMT (15:04 local time). Location and magnitude of this event are:

Latitude : 46°18.9' N
Longitude: 13°42.2' N
Depth: 7.9 km
Location: Kobarid (Slovenia)
Magnitude (from duration, MD): 5.1
Meccanismo focale: strike-slip (strike=135, dip=83, rake=173)
The maps show localizations and focal mechanism, respectively.

This earthquake has been felt clearly in a broad area of North-East Italy. A quick analysis of the recorded seismograms suggests that the July 12 event is a complex two-phase rupture. The starting focal mechanism is very similar to that of the event MD=5.6 of 04/12/1998. The combined effect of the two ruptures might explain the ground shaking that has been reported higher than that of 1998 in some cases.

The main event has been followed by a seismic sequence of about 70 aftershocks (with MD between 1.4 and 3.3), which are localized within the same area.

See seismograms of the main event recorded by the OGS-CRS Friuli Venezia Giulia seismometric network.

See seismograms of the main event and of the aftershocks recorded by the Trieste and Villanova broadband stations, managed by DST (University of Trieste) and by OGS-CRS.

Beginning from the 13 July a temporary network of 10 stations (see map) has been activated by OGS-CRS and INGV, in collaboration with the seismological service of the enviromental agency of the Republic of Slovenia(ARSO), in order to improve the monitoring of the seismic sequence.

The historical catalogues (NT4.1; Camassi and Stucchi, 1997) reports the following main events in the area:

· 24/04/1279, Cividale IMCS = VIII ;
· 11/06/1301, Cividale IMCS =VI ;
· 06/09/1403, Cividale IMCS =VII-VIII ;
· 26/03/1511, Gemona IMCS =VIII- IX (known also as the Idria earthquake);

Till the 1998 the registered seismic activity - the seismic network in Friuli is active from 1977 - is characterized by a low energetic level (MDmax=3.1-3.2) and it is quite scattered in the area.

From 1998, the area presents an high seismic activity, but always characterized by low levels of magnitudo.

The most relevant event, recorded by the seismic network, is the 12th April 1998 earthquake (MD=5.6) , located near Bovec.

The sequence of aftershocks of the 12th April 1998 event consisted in about 800 events, during all the 1998. The higher intensity aftershock was a MD=4.6 magnitudo earthquake.

Afterwards, the seismic activity in the area can be summarized in the following way:

· 1999: resumption of the seismic activity with 6-7 events characterized by 3.0<MD<3.8;
· 2000 e 2001: lower seismic activity (MDmax=2.9);
· 2002: resumption of the seismic activity between July and September 2002 with MDmax=3.8 (Kobarid (SLO));
· 2003: lower and less frequent seismic activity (MDmax=2.7).

The epicenter of the most recent earthquake is localized very close to the 12th April 1998 MD=5.6 event epicentral area. The figure describes the seismic activity in the area from 1977 to now.

Meccanismo focale dell'evento di MD 5.6 del 12 aprile 1998 (Bressan et al., 2003) e dell'evento di MD 5.1 del 12 luglio 2004. I cerchi rappresentano le repliche con MD = 2.5 dell'evento del 1998.
Il meccanismo focale del 1998 è stato elaborato con 71 polarità.
Il meccanismo focale del 12 luglio 2004 è stato elaborato con 60 polarità. Parte dei dati relativi alle polarità è stata cortesemente fornita dall'Istituto Nazionale di Geofisica e Vulcanologia (Roma), dalla rete sismometrica della Provincia Autonoma di Trento e dall'Agenzia per l'Ambiente della Repubblica Slovena (ARSO)- Servizio Sismologico (Ljubljana).

The focal mechanism of the 12 april 1998 event (MD=5.6) (Bressan et al., 2003) in comparison with the 12 July 2004 (MD=5.1). The circles are aftershocks (MD=2.5) of the 1998 event.
The focal mechanism of the 1998 event has been obtained using 71 polarities.
The focal mechanism of the 2004 event has been obtained using 60 polarities. Part of the data used was provided by INGV (Rome), Provincia Autonoma di Trento and Environmental Agency of the Republic of Slovenia (ARSO)-Seismological Service (Ljubljana) .