Barriers on seismogenic faults in central Greece

Abstract

Structural mapping, morphotectonic analysis and existing seismological data are synthesized to characterize barriers—regions of high strength along the fault which can impede or arrest rupture propagation—on the most active and prominent traced fault zones in central Greece. Inhomogeneous and non-conservative barriers are the two different structures that have been identified on the Eliki fault (in northern Peloponnesos), and the Kaparelli and Atalanti fault zones (in Sterea Hellas), respectively. The Eliki fault consists of two colinear segments of different rupture characteristics that intersect at an inhomogeneous barrier. The eastern fault segment has had, in Late Quaternary, repeatedly activated earthquake sequences, whereas the western segment remained unaffected 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—strong stable barriers—that effectively blunt the fault displacements and permit independent deformation of the fault segments. Earthquakes on these fault zones occur when the asperities fail. Repeated deformation and evolution of faulting change these asperities into non-conservative barrier structure. That is, surface rupturing is accommodated by a new, third direction of faulting developed in the zone of intersection between the two adjacent oblique segments of the primary fault zone. This third direction of faulting involves a major cumulative dip slip within the barrier region and it is responsible for repeated earthquakes during the Quaternary time. In response to this faulting process, a primary bent fault zone activated by repeated earthquake events tends to be curvilinear in trace and preserves a perched basin on its footwall block. The proposed rupture model of fault zone bends by a third direction 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 inherited strikes; and (2) the initiation of earthquakes from the fault zone bends.