Growth folding and active thrusting in the Montello region, Veneto, northern Italy

The Montello is an elongated hill about 15 km long and 5 km wide located so uth of the Venetian Alps front and similar to 100 km southwest of Gemona, s ite of the destructive M-s similar to 6, 1976 earthquake sequence, Mio-Plio cene strata in the core of the hill are folded. Seven Quaternary terraces a cross the western termination of the anticline have also been folded and up lifted. The terraces flank the abandoned Biadene valley, a former course of the Pia ire river which now flows eastwards along the north side of the hi ll. Topographic profiles along and transverse to the valley and terraces ar e used to measure the progressive development of the anticline. Fossil rema ins and archaeological sites dated with C-14 suggest that the Biadene paleo valley was abandoned between 14 and 8 ka (11 +/- 3 ka). The successive terr aces appear to have been emplaced at the onset of interglacials and interst adials, since about 350 ka. The best fitting terrace ages suggest vertical uplift; rates of about 0.5 mm/yr before 17% ka and of about 1 mm/yr after 1 21 lia. The Montello thus appears to be a growing: ramp anticline on top of an active, north dipping thrust; that has migrated south of the mountain i nto the foreland. Modeling the deformation of the terraces as a result of m otion on such a thrust ramp requires that it propagated both south and upwa rds with time but with a, constant; slip rate (1.8-2 mm/yr). For at least 3 00 kyr the lateral growth of the anticline kept pushing: the course of the Piave river southwestwards, at a rate at first of 10 mm/yr, and then 20 mm/ yr, Though the growth rate doubled more than 120 kyr ago, the anticline kep t a constant height/length growth ratio (similar or equal to 20) implying: self-similar depth/length growth of the thrust underneath. The clustering o f historical earthquakes north of Treviso suggests that the thrust responsi ble for ongoing folding of the 'Montello slipped seismically three times (7 78, 1268, 1859 A.D.; intensity I greater than or equal to VIII) in the last 2000 years, with events of maximum magnitude close to 6 and with average r ecurrence time between 500 and 1000 years. NW shortening on NE-SW trending thrusts along: the Venetian Alps front is compatible with the direction of convergence between Africa and Europe but does not suffice to absorb this c onvergence.