A Proposal of Instrumental Seismic Intensity Scale Compatible with MMI Evaluated from Three-Component Acceleration Records

Abstract

Seismic intensity provides useful information on the regional distribution of earthquake effects and has been used to assess seismic hazards and damages. The concept of intensity has been considered as a method to classify severity of the ground motion on the basis of observed effects in the stricken area. In 1996, the Japan Meteorological Agency (JMA) developed a new seismic intensity measurement scale using three-component strong ground motion records in order to provide a measure of the strength of the seismic motion, which is compatible with the existing JMA intensity scale. By applying a band-pass filter to the frequency domain and a vectoral composition of the three components in the time domain, the JMA seismic intensity scale (IJMA) can be calculated without subjective judgement. In this study, we apply the IJMA method to the acceleration records of three recent significant earthquakes in California. For a Modified Mercalli Intensity (MMI) between IV and VIII, a new relation between MMI and log a0, obtained in the process of calculating the new IJMA, is given by the equation MMI=3.93 log a0−1.17. We propose this relation as a new instrumental seismic intensity (IMM) compatible with the California region MMI.