Historical Seismograms - Evidence from the AD 2000 Izu Islands ...

330 S. Riad, H. Meyers, and C. Kisslinger1 3.0 3’5++no. of events used 4380.0-0.5--+ + ++ ++ + -+ +t+ -ML - 0.5 lo = 1.361 logh - 0.133I I I I I I I I I I I I II 1 10.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8Log hFigure 4. ML - I. VB. log h relation for the Middle East.where N is the cumulative number of earthquakes per year of magnitude 2 ML.The constant a depends on the period of observation, the size of the investigatedarea and on the level of the seismicity as well. The constant b is assumed to berelated to the geologic age of the seismotectonic zone (Miyamura, 1962), as well asdepending on other factors such as heterogeneity of source medium and ambientstress level (Mogi, 1962). The value of b has been reported to vary between 0.5 and1.2 for the USSR, and between 0.9 and 1.2 for the Caucasus (Solov’ev, 1961). On aworldwide scale b was found in the range 0.4 to 1.8 (Kbrnik, 1969). High values ofb (1.0-1.8) have been found in circum-Pacific and Alpine orogenic zones, includingisland arcs; medium values of b (0.6-0.7) correspond to continental rift zones andplatform blocks; low values of b are typical for shields (Miyamura, 1962).Recurrence-rate relations were determined for the Middle East in general and forselected areas for the period 1900-83 (Table 7). Relations obtained for the MiddleEast are given in the form:logN = 7.73 - 1.306M~; (7)log N = 8.44 - 0.979 I,, (8)where N is the cumulative number of earthquakes per year of magnitude 2 MLor intensity 2 I,. Plots representing these relations are shown in Figures 5 and 6.Plots representing the originally reported value of the given parameter (ML or I,)are also shown. The misleading results of using incomplete information is obviousin these plots.