Abstract
For mapping the seismic activity tlie earthquake energyreleaseil per square degree per liundred years was determined, and tlie valuesobtained were used for drawing isoenergetical lines. Two maps constructedin this way for the periods 1710-1959 and 1841-1959 show clearly tliat theearthquake activity in the Greek area is concentrated, for the most part, alongthe large fault zone bordering the western and southern coasts of Greece.It is believed tliat this fault zone marks the trend of a marginai geosyncline,which is now in the course of development in the Eastern Mediterranean.Tlie map of earthquake efflciency in Greece sliows clearly tliat the mainpart of the earthquake energy released in the Greek area comes frolli twowell developed centres of higher seismic activity, located along the abovementionedlarge fault zone.
Highlights
T h e first really constructivecontributionstowardthe solution of theproblem for aquantitativedetermination of seismicity were madeafterthe use of t h e concept of magnitude, whieh allowed t h e calculation of t h e seismic energy of eartquakes
I t is rather generally accepted that the quantitative representation of seismicity sliould be based, directly or indireetlv, on thesummarized seismic energy of earthquakes or on t h e roots of theenergy values (Ritsema, 1954; Amami, 1956; Bàth, 1956)
Since these values must be determined mainly from strong earthquakes, comprising the overw helmingpart of thetotal seismic energy of earthquakes, it was early recognized t h a t this metliod could notafforda reliable measure of seismicity; t h i s due to lack of instrumentaidata covering a t least t w o seismic active periods (Galanopoulos, 1956)
Summary
T h e first really constructivecontributionstowardthe solution of theproblem for aquantitativedetermination of seismicity were madeafterthe use of t h e concept of magnitude , whieh allowed t h e calculation of t h e seismic energy of eartquakes. The m a p of earthquake effìciency in Greece shows clearly t h a t the main p a r t of the earthquake energy released in the Greek area comes from two well developed centres of higher seismic activity, located along the above-mentioned large fault zone (see Fig. 1 and 3). In the centre situated in the south-eastern Aegean Sea, the earthquake activity rises from 4 to 5 and culminates in the area between Crete and Rhodes with six shocks of magnitude 6.8 per square degree per hundred years. N denotes the number of earthquakes of a given energy class, log E , having been observed in the Greek area under consideration within the corresponding time intervals. ON, 37". 5N, 39". 8N, 40". 2N, 37" V2N, 37" 3/4N, 19". 6E 19°. 6E 19". 7E
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