Abstract

Field investigations conducted immediately after the Gulf of Corinth earthquake of 24 February 1981 provide an extensive set of data on intensity at different sites for the main shock and two of its principal aftershocks. Each site of intensity observation was characterized by the local site geologic condition. The hypocenters of the three shocks were relocated by using the joint epicenter location technique, with the aftershock of 12 March, 1981 (01:49 UTC), recorded by six portable stations as well as stations of the Greek National Seismographic Network, as the calibration event. Isoseismal maps prepared by using all intensity data for the three shocks were used to derive new attenuation relations. Analysis of the intensity residuals (observed-calculated intensity) shows that local site geologic condition has a significant effect on the intensity observed at a site. On an average, under similar circumstances, sites located on soil foundations experience about one intensity unit more shaking than sites located on rock foundations. Likewise, sites located on Neogene sediments (intermediate foundation condition) experience about 12 unit greater intensity effect than sites located on rock foundations. Attenuation relations derived by using intensity data for the three February-March 1981 earthquakes show lower attenuation than the relation derived by using published isoseismal maps for 19 earthquakes which occurred in the Corinth-Saronikos region during 1861 to 1975.

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