On the Correlation of Seismic Intensity with Fourier Amplitude Spectra

Abstract

This paper presents a method for estimating the seismic intensity (MMI or MSK scale) using Fourier amplitude spectra of ground acceleration. The method implies that the severity of earthquake ground motion is determined by spectral amplitudes in a relatively narrow frequency band: so-called “representative frequencies”, at decreasing frequencies (from 7-8 Hz for small intensities to 0.7-1.0 Hz for MMI=VIII-IX) with increasing intensity level. It is examined through estimation of probable intensity at a site using recordings of recent earthquakes in several seismic regions, and prediction of intensity distribution patterns for the Coalinga, California earthquake of May 2, 1983, and the Spitak, Armenia earthquake of December 7, 1988. Seismic hazard maps, in terms of intensity levels based upon the proposed approach, should describe regional features of seismic waves excitation and propagation, as well as local ground conditions.