Macroseismic Observations Research Articles

Surface fault traces and fault plane solutions of the May–June 1978 major shocks in the Thessaloniki area, Greece.

It is shown that the foci of the recent earthquakes in the Thessaloniki area of northern Greece are located in an arcuate seismic zone which is associated with the Serbomacedonian geologic zone. Three main lines of fracture have been observed in the epicentral area after the May–June 1978 earthquakes. Field and macroseismic observations as well as fault plane solutions for the main shock and for the largest foreshock show that both earthquakes are due to a strike slip sinistral motion with a small reverse component on a steeply dipping and trending southeast-northwest fault.

Investigations of intensities, aftershock statistics and the focal mechanism of Friuli earthquakes in 1975 and 1976

Isoseismal maps, derived from macroseismic observations in the epicentral region and in Switzerland for the Friuli earthquake of 6 May 1976, are presented. From these maps a focal depth ofh=8 km and a related attenuation factor of α=0.001 can be estimated. An analysis of aftershocks reveals a slope ofp=0.85 for the logarithmic relationship between number of events and time. A firstmotion study for a preceding earthquake in Friuli on 24 March 1975, gives two possible fault plane solutions, both indicating a North-South direction of the axis of maximum shortening of the earth's crust.