Coseismic crustal deformation on a fault zone defined by microseismicity in the Pavliani area, central Greece

Abstract

Pavliani is an area of high microseismicity in northern central Greece. There is no evidence in the historical record of large damaging earthquakes in this area since at least 600 BC. We examine contemporary crustal deformation in this area using microearthquake data recorded during 1983–84 by the Volos seismic network, principally, and to a lesser extent by the Patras seismic network. The microseismicity (1–4.6 ML) defines an approximately vertical fault zone trending WSW‐ENE, of 55 km length and 25 km depth. the fault‐plane solution for the 4.6 ML earthquake shows a strike consistent with the trend of the microseismicity zone, and an extension direction consistent with many large earthquakes in central Greece associated with the extensional greater Aegean. Spectra of the microearthquakes are estimated using P waves obtained by selective windowing designed to exclude other P phases from the coda; seismic moments in the range 1–95 x 1012 N m are obtained, accompanied by estimates of seismotectonic source parameters, including source radii, average stress drop and average coseismic slip. of prime utility is an excellent correlation found between seismic moment and magnitude, and with coseismic slip. This allows heterogeneity in the distribution of individual microearthquake source parameters to be mapped onto the vertical fault‐zone plane and the history of coseismic deformation for the whole seismicity observed during 1983–84 to be examined using cumulative slip and moment‐release rate. Peaks of high moment‐release rate occur in the east and centre of the fault zone. That in the east is dominated by a few large moment‐release events; that in the centre by a large number of small events. Both moment‐release‐rate peaks, despite their different component seismicity, are associated with high cumulative coseismic slip. Only the eastern peak is also associated with high stress drop; it is also shallower, and therefore any surficial interaction is less likely to be attenuated. the surface projection of this peak is within 3 km of a mapped normal fault coincident with an Alpine thrust front delineated by a major scarp of Mesozoic limestone. Surface evidence of recent movement on this normal fault is only slight. Friable fault gouge is seen at a few localities. Displacement could not be determined because the limestone surfaces are deeply weathered and lack kinematic indicators. However, considering the whole fault zone as a cohesive entity, and using a Brune estimate of slip at the current moment‐release rate throughout the present extensional tectonic regime, suggests a total vertical displacement of order 175 m, similar to the elevation of the scarp. Copyright © 1995, Wiley Blackwell. All rights reserved