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Variation of strong motion intensity, root mean square of ground acceleration and time-duration in seconds obtained from 83 accelerograms of 18 earthquakes with magnitudes between 5 to 7.7 were investigated considering four definitions of strong section of accelerograms given by Vanmarcke-Lai; Bolt, Trifunac-Brady and McCaan-Shah. Strong motion intensities were calculated for all definitions of strong duration. Even though, durations in seconds and root mean square of ground acceleration values resulted quite different among the four definitions of strong sections, both durations in seconds and root mean square of acceleration squared values tend to compensate each other to yield the same strong motion intensity for each definition used. Q-ratio as defined by Vanmarcke-Lai (Peak Ground Acceleration divided by root mean square of acceleration) was found not constant but instead it varied significantly for all strong motion definitions. Similarly, ratio of strong motion intensity over peak ground acceleration squared as defined by Vanmarcke-Lai holds linear for time durations less than 20-30 seconds for all definitions, afterwards it shows large dispersion. Finally, Vanmarcke-Lai time duration in seconds appears to increase from near field distance up to a certain medium distance after which it starts to decrease.

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