Abstract
A method is proposed for the calculation of a comparable measure of the earthquake risk from the coefficient- a* of the N(M)- relation normalized to a standard slope b, and a standard area. In comparing the earthquake risk in Greece and Southern California, it was found that the average and the maximum earthquake risk in the area of Greece is about one half and two times, respectively, the average earthquake risk in Southern California. Another method is proposed for the calculation of the recurrence rates for earthquakes of a given magnitude range in small areas for which the existing earthquake magnitude data are not abundant and good enough for determining a reliable recurrence curve. In view of the large fluctuation of the actual recurrence rates for earthquakes of a given magnitude -disregarding the accuracy of the available data — mapping in the form of the earthquake frequency isolines seems to be meaningless for engineering purposes.
Highlights
Investigating the seismieity of some Greek areas a n d a score of aftershock sequencies in Greece, I was led to t h e conclusion thatthe slope of the cumulative curve, log N = a — bM, depends largely, if n o t entirely, on the average focal depth of theearthquakes considered Galanopoulos (l-2)
Assumingthatthe slope of t h e recurrence curvedepends entirely on theaverage focal depth of t h e earthquakes considered, we may reliably estimate the earthquake risk in the seismic regions from the corresponding recurrence curves normalized to a standard slope and a standard area
The earthquake risk determined by the proposed method is in fair accordancewiththegrading of t h e seismic regions appeared in thestrain release m a p of theSouthern California region, 193-1 to 1963 ( l l )
Summary
SUMMARY. — A method is proposed for the calculation of a comparable measure of the earthquake risk from the coefficient- a* of the N(M)relation normalized to a standard slope b, and a standard area. In comparing the earthquake risk in Greece and Southern California, it was found thatthe average and t h e maximum earthquake risk in the area of Greece is about one half and two times, respectively, the average earthquake risk in Southern California. Another method is proposed for the calculation of t h e recurrence rates for earthquakes of a given magnitude range in small areas for which t h e existing earthquake magnitude data are not abundant and good enough for determining a reliable recurrence curve. Vista la grande gamma nella quale variano i periodi della ricorrenza attuale per terremoti del tipo suddetto —- d a t a la poca precisione
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