THE ATTENUATION OF GROUND ACCELERATIONS IN EUROPE

The paper presents predictive relationships for horizontal and vertical peak ground accelerations derived from 529 triaxial strong-motion records generated by 219 shallow earthquakes in the European area. If no account is taken of the focal depth, the attenuations of peak horizontal and vertical accelerations, in g, are given by log(a(h)) = - 1.09 + 0.238M(s) - log(r) - 0.00050r + 0.28P and log(a(v)) = - 1.34 + 0.230M(s) - log(r) + 0.27P where r = (d2 + 6.0(2))1/2, d is the source distance in km and M(s) is the surface-wave magnitude; P is 0 for 50-percentile values, 1 for 84-percentiles. If we allow for the effect of the focal depth h, in km, the corresponding equations for a(h) and a(v) are found to be log(a(h)) = - 0.87 + 0.217M(s) - log(r) - 0.00117r + 0.26P and log(a(v)) = - 1.10 + 0.200M(s) - log(r) - 0.00015r + 0.26P where r = (d2 + h2)1/2. The mean ratio of the peak vertical to horizontal acceleration is found to be almost independent of magnitude and distance, and equal to 0.5.