Earthquake Ground Motion and Response Spectra

Abstract

This chapter surveys the state-of-the-art work in strong motion seismology and ground motion characterization. Methods of ground motion recording and correction are first presented, followed by a discussion of ground motion characteristics including peak ground motion, duration of strong motion, and frequency content. Factors that influence earthquake ground motion such as source distance, site geology, earthquake magnitude, source characteristics, and directivity are examined. The chapter presents probabilistic methods for evaluating seismic risk at a site and development of seismic maps used in codes and provisions. Earthquake response spectra and factors that influence their characteristics such as soil condition, magnitude, distance, and source characteristics are also presented and discussed. Earthquake design spectra proposed by several investigators and those recommended by various codes and provisions through the years to compute seismic base shears are described. The latter part of the chapter discusses inelastic earthquake spectra and response modification factors used in seismic codes to reduce the elastic design forces and account for energy absorbing capacity of structures due to inelastic action. Earthquake energy content and energy spectra are also briefly introduced. Finally, the chapter presents a brief discussion of artificially generated ground motion.