Ongoing shortening in the Dinarides fold-and-thrust belt: A new structural model of the 1979 (Mw 7.1) Montenegro earthquake epicentral region

Abstract

This study focuses on structure and kinematics of the 1979 Mw 7.1 Montenegro earthquake. Although this event represents the strongest instrumentally recorded event in the entire Dinarides-Hellenides fold-and-thrust belt, no tectonic model relating this event to any particular fault existed so far. We combined onshore geological information with well logs, seismic lines, bathymetric data, seismotectonic and seismological data as well as cross-section balancing techniques into a new structural model for the area. Our results suggest that main shock and strongest aftershock (Mw 6.2) occurred on the NE-dipping basal thrust of a largely Palaeogene-age nappe system involving Cretaceous neritic carbonates. Ongoing propagation of this thrust system is documented by the existence of elongated ridges located 15 km offshore. Reflection seismic and bathymetry data reveal that the ridges form crests of actively growing fault-related anticlines. Slip distribution models of the strongest events imply that the basal thrust below the ridges accommodated up to 2.7 m of coseismic displacement. Ongoing shortening along the basal thrust also induced surface uplift of structurally higher thrust imbricates, evidenced by dry valleys incising onshore anticline crests. Combining all evidence, we speculate that the observed structural and geomorphic features resulted from repeated seismogenic faulting events as in 1979.