BARRIERS ON SEISMOGENIC FAULTS IN CENTRAL GREECE

Structural mapping, morphotectonic analysis and existing seismological data are synthesized to characterize barriers-regions of high strengt h along the fault which can impede or arrest rupture propagation-on th e most active and prominent traced fault zones in central Greece. Inho mogeneous and non-conservative barriers are the two different structur es that have been identified on the Eliki fault (in northern Peloponne sos), and the Kaparelli and Atalanti fault zones (in Sterea Hellas), r espectively. The Eliki fault consists of two colinear segments of diff erent rupture characteristics that intersect at an inhomogeneous barri er. The eastern fault segment has had, in Late Quaternary, repeatedly activated earthquake sequences, whereas the western segment remained u naffected by these events. The Kaparelli and the Atalanti fault zones are the WNW and ENE fault segments of a single primary fault zone with a surface trace bent. The fault zone bends represent asperities-stron g stable barriers-that effectively blunt the fault displacements and p ermit independent deformation of the fault segments. Earthquakes on th ese fault zones occur when the asperities fail. Repeated deformation a nd evolution of faulting change these asperities into non-conservative barrier structure. That is, surface rupturing is accommodated by a ne w, third direction of faulting developed in the zone of intersection b etween the two adjacent oblique segments of the primary fault zone. Th is third direction of faulting involves a major cumulative dip slip wi thin the barrier region and it is responsible for repeated earthquakes during the Quaternary time. In response to this faulting process, a p rimary bent fault zone activated by repeated earthquake events tends t o be curvilinear in trace and preserves a perched basin on its footwal l block. The proposed rupture model of fault zone bends by a third dir ection of faulting during large earthquake events and is suitable for widespread application in Greece, regarding: (1) the interpretation of the distribution of fault strikes between dominant WNW and ENE inheri ted strikes; and (2) the initiation of earthquakes from the fault zone bends. Copyright (C) 1996 Elsevier Science Ltd