LONG-TERM CRUSTAL DEFORMATIONS IN NE ITALY REVEALED BY TILT-STRAIN GAUGES

Tilt and strain gauge records are analysed to determine the long-term variations in space and time of the strain field in the Friuli area (N E Italy), located at the eastern boundary of the Adria plate. For such long-term variations a deep crustal origin is supposed. Spectral and cross-correlation analyses show that the strain energy involving a lar ge area is polarized in two main directions, N20W and N70E, the first one characterized by aperiodic (or very long period, undetectable by t he present analysis) variations, the second one by a period of about 8 years. The direction of the aperiodic motion (N20W) is normal to the Alpine chain, and parallel to the maximum horizontal compression actin g in the Alpine area, whereas the direction of the 8 year period motio n (N70E) is normal to the Dinaric Alps chain, and coincident with the maximum horizontal compression acting on the eastern boundary of the A dria plate, in the Balkans region. To explain such results, and partic ularly those related to the N70E direction, slow-travelling stress-str ain waves are hypothesized.