Seismic Monitoring in Northeastern Italy: A Ten-yearExperience E. Priolo, C. Barnaba, P. Bernardi, G. Bernardis, P. L. Bragato, G. Bressan, M. Candido, E. Cazzador, P. Di Bartolomeo, G. Duff, S. Gentili, A. Govoni, P. Klinc, S. Kravanja, G. Laurenzano, L. Lovisa, P. Marotta, A. Michelini, F. Ponton, A. Restivo, M. Romanelli, A. Snidarcig, S. Urban, A. Vuan, and D. Zuliani INTRODUCTION Northeastern Italy (NEI), bordering Slovenia and Austria, consists of the Friuli-Venezia Giulia, Veneto, and Trentino- Alto Adige regions. The area includes the Italian part of the southeastern Alps to the north, and the Veneto and Friuli Plains to the south. Together with its neighboring regions of southern Austria and western Slovenia, this is possibly the most tectonicaUy active area of the Alpine Arc in the present age. The region features the highest seismicity in the Alps, although it can be rated only as moderate level in general terms. According to the CPTI04 catalog (CPTI Working Group, 2004), six earthquakes with MCS intensity greater or equal to IX have struck the area in the last 1,000 years, all with estimated magnitude not exceeding M 6.6 (Figure 1). The last of these occurred in central Friuli on 6 May 1976 (M E 6.4). Except during the 1976 sequence, magnitude 5.5 or greater earthquakes have occurred only four times in the last century: 1924 and 1928 Tolmezzo, 1936 Cansiglio (Slejko et al., 1989), and 1998 Bovec, Slovenia, just across the Italian border (Bajc et al., 2001). Instrumental seismological observations in NEI started at the end of the 19th century with a few observatories in Italy and the former Hapsburg Empire. Since that time, the reference station for the area is in Trieste (Finetti and Morelli, 1972). In 1931 it was taken over by what is now the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS). It later became part of the World Wide Standardized Seismographic Network (WWSSN, station code TRI-117). Since 1996 the station has been equipped with a Streckeisen STS 1 broadband seismometer managed in collaboration with the Dipartimento di Scienze della Terra dell'Universit~l di Tri- este (DST). It is included in the Mediterranean Very Broad- band Seismographic Network (MEDNET) as station TRI (http://bbtri.inogs.it). In 1977, OGS activated the first five short-period verti- cal seismometers of the Seismometric Network of Friuli-Ven- ezia Giulia in the area of the 1976 ME 6.4 Friuli earthquake. Since that time OGS has installed more stations in Friuli- Venezia Giulia and established a new network in the Veneto region. Together, these two networks constitute the Short- Period Seismometric Network of Northeastern Italy (NEI network, Figure 1). In 1994, the network was substantially improved with the installation of a new acquisition system that provides good-quality digital data. This system provided the opportunity to implement new tools for automatic and manual data processing to support research activities and emergency response by civil protection authorities. In the fol- lowing sections we describe the technical characteristics of the network, review the main results achieved in the last ten years, and illustrate the current developments. Data from the network are available on request. The use of catalog data is unrestricted, while that of the waveforms is subject to approval by OGS. Proposals for cooperation with OGS are encouraged. Data requests must be sent to datacrs@inogs.it. SHORT-PERIOD SEISMOMETRIC NETWORKOF NORTHEASTERN ITALY The NEI network is run by the Centro di Ricerche Sismolog- iche (CRS), a department of OGS located in Udine. It has 21 stations (Figure 1; Table 1). Seventeen stations are equipped with a 1-Hz three-component Lennartz LE-3D seismometer; one has a Mark L4C 1-Hz vertical seismometer installed in a 100-m-deep borehole; two have a velocimetric/acceleromet- ric couple (BAD and BOO; see Table 1); one (UDI) is equipped with a Guralp CMG-fT accelerometer. The data are transmitted by UHF radio to the CRS cen- tral station in Udine using the Lennartz MARS88/RC digi- tal-acquisition system. It is a hardware/software integrated system that supports signal digitalization, data transmission, storage, and access to data for automatic and manual process- ing. Besides the sensors, each remote station includes: 9 MARS88 digital data logger with 120-dB dynamic range set to acquire at 62.5 sps or 125 sps with an anti-alias fil- ter at 25 Hz or 50 Hz, respectively. The data are stored 446 Seismological Research Letters Volume76,Number4 July/August2005