On Intensity Definitions of Earthquakes

One of the most fundamental problems in earthquake engineering is to properly determine the intensity or strength of an earthquake. Such intensity may be defined as a function of variables characterizing the excitation or the structure, or both, and thus can be used in direct response computations. So far there has been no unique definition for the earthquake intensity, although Housner's definition (5)² seems to be the one most commonly used. The recent tendencies in research activities as well as industrial practices to use stochastic representations for the earthquake accelerations (1,6,7,13) and probabilistic methods of analysis for the structural response (4,8) have imposed considerable confusion and difficulty in properly defining the groundmotion intensity. It is the purpose of this technical note to study and compare various earthquake intensity definitions and to describe their applicability. Emphasis is placed on finding the time-varying rms accelerations of existing strong-motion earthquake records and several simulating stationary and nonstationary random models of earthquakes.