On 6 May 1976, a magnitude 6.4 earthquake struck the Friuli region of northeastern Italy near the towns of Gemona and Venzone. Although it was not as large as some previous earthquakes in Italy, its severe ground motion (up to 0.36 g) affected an area with numerous historical towns, resulting in 989 fatalities and 45,000 people left homeless. At least four other destructive earthquakes with epicentral intensity greater than or equal to IX on the Mercalli-Cancani-Sieberg scale have occurred in the Friuli region in the last 5 centuries (1511, 1700, 1794, and 1928) [Slejko et al., 1999].
To better understand the seismic hazards of this vulnerable area, a network of continuously operating Global Positioning System (GPS) receivers—the Friuli Regional Deformation Network (FReDNet)—was installed to monitor the regional distribution of crustal deformation (Figure 1).
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