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The misuse of earthquake intensity by engineers in design and the growing awareness of the actual acceleration at ground surface near earthquakes were two key items in Professor Ambraseys' introduction.Intensity, like other semi-empirical measures when assessed at a large number of points might show regular distribution patterns and its use by seismologists had helped determine relative focal depths and energy absorption coefficients. Intensity was, however, a measure of the effect of ground motion on man-made structures and it varied from place to place. Engineers in attempting to relate it to design parameters such as acceleration by a multitude of empirical formulas under pressure of practical need were nevertheless overlooking the subtleties involved in its definition and assessment.Professor Ambraseys showed the scatter diagram of maximum ground acceleration versus reported intensities for the period 1933-1943: then there was an obvious correlation trend. The plot for a 20 year period showed more scatter and currently fitting an empirical formula was not possible. This did not mean that intensity could be abandoned as a means of conveying useful information of earthquakes: rather it should be looked upon as were Atterberg limits in soil mechanics. Engineers did not use them alone to design dams! Professor Ambraseys pleaded for more information from simple instruments, and fewer attempts to invent new intensity scales, particularly international ones.In the past one of the most popular design parameters had been acceleration-one need only multiply by mass to obtain a force-and its prediction had attracted the attention of many seismologists and engineers. Numerous attempts had been made to relate maximum ground acceleration with epicentral or focal distance, and with intensity and magnitude. From a study of strong motion records Professor Ambraseys had found that for all practical purposes there was no significant correlation between magnitude, distance and acceleration in the near field; but at larger distance or for small acceleration these three variables became more interdependent.With regard to acceleration in the epicentral regions of a strong earthquake, Professor Ambraseys reminded his audience that well before the advent of recorders some idea of acceleration was gleaned by observing overturned objects. The famous Meopolitan earthquake of. 1857 probably had an acceleration of 3&50% g, and at Imaichi in 1949 a figure of 95% g was deduced. Indeed in some of these large events prior to 1949 the apparent vertical motion exceeded 100% g. Many doubted these large values, and when the first good strong motion record from the Long Beach earthquake showed an undisputable 23% those doubters felt vindicated. In 1940 however the El Centro earthquake record displayed acceleration larger than 30% g. For two generations of engineers the upper limit of 30% g, a view supported by Hawsner, was popular, but with a series of strong motion records from Matsushiro (57% g) Parkfield (51% g), Koyna (63% g), Pacoima (124% g)...

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