Correlations of the recorded peak acceleration, velocity and displacement, and the Modified Mercalli intensity have been carried out for 57 earthquakes and 187 strong-motion accelerograms recorded in the Western United States. Correlations of peak acceleration with intensity, characterized by the data scatter exceeding one order of magnitude, have lead to average peak accelerations which are higher than those reported by a majority of previous investigators. New correlations, also characterized by scatter of data of about one order of magnitude, have been presented for peak velocities and displacements of strong ground motion versus Modified Mercalli intensity.
Grouping of all recorded data according to the geology underlying the strong-motion accelerograph stations was carried out and permitted a study of the possible effects that local geology might have on the peaks of strong-motion acceleration, velocity, and displacement. Results of this analysis are as follows: (1) For ground shaking of a particular Modified Mercalli intensity, average peak acceleration recorded on hard rock is higher by a factor less than about two than the average peak acceleration recorded on alluvium; (2) the effect of local geology on the average peak velocity leads to marginally higher peak values on alluvium; and (3) the peak ground displacements are larger, by a factor less than two, when recorded on alluvium rather than on hard rock.