On the intermediate earthquakes in Greece*

Abstract

Abstract The identification by Gutenberg and Richter of many earthquakes in Greece as earthquakes occurring at intermediate depth has led the author to investigate the form of their records written at Athens. His conclusions are: (1) The criterion for the seismograms of near-by intermediate shocks seems to be the distinct onset of the P wave, combined with a gradual diminuation of its amplitude which permits the second phase to appear clearly on the record. (2) Intermediate shocks are missing in the region of the Ionian Sea. (3) Unquestioned intermediate shocks appear to be limited chiefly to the region of the Aegean Sea. (4) The causative mechanism of the normal and deep shocks seems now and then to be changed in a given region within a short time. (5) The similarity of the seismograms written at Athens by the shocks of a given region appears to depend upon the amount of energy released, the depth of the source, and the direction of the earthquake fault relative to the bearing of the source-station line. (6) The Mohorivičcić discontinuity seems to reach, in the area of the Aegean Sea, a depth probably greater than 50 km.