The Friuli (NE-Italy) tilt/strain gauges and short term observations

Abstract

The tilt/strainmeter network of the Department of Earth Sciences of the University of Trieste, has by now a long history of records, the Trieste Grotta Gigante horizontal pendulum station having been set up in 1959 and the Friuli tilt/strainmeter stations in 1977. Since then the stations have been continuously recording the strain-rate in one of the most seismic areas of the Alpine arc, giving invaluable information on crustal deformation in a tectonically active area. Although maintaining essentially the same mechanical features from the time of installation, the instrumentation has undergone modernization, in order to apply recent technical developments to the network. This regards mainly data acquisition, which now, except for one station, is digital. The data are all available and are stored in the Deformation-Database of the Department of Earth Sciences. At first a description of the essential technical and mechanical properties of the instrumentation constituting the network is given. The mean power spectrum of all instruments covering five decades is presented, which is a powerful means to compare the quality of different stations. Following theoretical considerations of the expected pre- or coseismic deformation accompanying local events, the observations of those events is presented, which ought to give the greatest signals. The coseismic steps are modeled for those events for which a fault plane solution was available.