Fault Parameters of the 1980 (Mw 6.5) Volos, Central Greece, Earthquake from Inversion of Repeated Leveling Data

by Antonis G. Drakos, Stathis C. Stiros, and Anastasia A. Kiratzi

Abstract

The 1980 Volos (Almyros) seismic sequence, the last of an unusual clustering of earthquakes with surface magnitude 6.0–7.0, which hit Thessaly (central Greece) between 1930 and 1980, is among the least studied recent earthquakes in Greece. Repeated measurement of three first-order spirit leveling traverses crossing the meizoseismal area of the seismic sequence indicates that between 1970/1971 and 1988/1989 a subsidence of about 35 cm is observed at the Almyros Neogene-Quaternary graben. The observed displacements are significant against random and systematic errors and can be assigned to the 1980 earthquake sequence. Inversion of leveling data using an elastic dislocation model, constrained by structural and seismological data indicates that the mainshock (M_w 6.5) and the largest aftershock (M_w 6.1) were probably associated with reactivation of two subparallel, homothetic normal faults marking the northern margin of the Almyros Neogene-Quaternary graben.

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