Comparative Analysis of Two Methods for Instrumental Intensity Estimations using the Database Accumulated during Recent Large Earthquakes in Japan

Abstract

A database containing records from nine large earthquakes in Japan, obtained by K-NET and KIK-net strong motion stations, was used for the analysis of two techniques for the estimation of instrumental seismic intensity from accelerograms. The first technique is the standard method for JMA intensity evaluation from filtered three-component accelerograms. The second technique is the so-called FAS-intensity, which was developed for MM and MSK scales and which is based on the correlation between levels of the Fourier Amplitude spectrum (FAS) and observed intensity. The relation between these two types of instrumental intensities ( JMAI and spectral MMI) may be described by linear function for intensities larger than JMAI 3.5–4 and MMI 5.0–5.5, but large discrepancy arises at small intensities. The variation is most probably caused by differences in the spectral content of the ground motions, since the JMAI calculation is sensitive to the spectral amplitude within a narrow frequency band around 0.5 Hz.