Recent earthquake activity in Trichonis region and its tectonic significance

SUMMARY. - The aftershock activity associated with the central Greece (Trichonis Lake) earthquake of |une-Dec. 1975, has been studied, with emphasis on the time and magnitude distribution. It has been found that the value of b, in Gutenberg - R i c h t e r ' s relationship was near the same for the primary as well as the secondary or second order aftershocks of the sequences, but depends upon the focal depth. A correlation between the calculated focal mechanisms and the associated stress components to the distribution pattern of meizoseismic effects as well as to the geological structure of the seismic region was found. The seismic region lies at the top of an anticline which was found moving downwards, apparently due to compressional stresses. Within the series of three earthquakes the progress of the destruction of the buildings was observed and reported. The interest is concentrated to modern buildings out of reinforced concrete and infill brick walls. The relatively unexpected rather bad performance of the later case of buildings was compared to that of the traditional small houses out of brick or stone masonry, the behaviour of which may be considered as better from what it was expected.