IJMA-based evaluation of ground motion recordings from Vrancea intermediate-depth earthquakes

Abstract

A ground motion database of about 600 recordings from 15 intermediate-depth Vrancea earthquakes which occurred in the period 1977–2024 was assembled for this study. The Japan Meteorological Agency intensity (I_JMA) is evaluated for all the recordings in the database in order to have a more objective measure of the ground motion intensity since I_JMA takes into account both the amplitude, and the frequency content, as well. The results of the analyses show no visible trends in the variation of I_JMA with the horizontal peak ground acceleration as a function of the soil class. The ANOVA method shows that the earthquake magnitude is the most relevant parameter influencing I_JMA, while the soil class is the least relevant one. It has also been observed that the normal probability is appropriate for modelling the distribution of I_JMA for a given seismic event. Moreover, it has been observed that the horizontal components having the largest I_JMA for the largest five earthquakes in the database (the events of 1977, 1986, 1990 and 2004) can be considered as being pulse-like. The coefficient of variation for the PGA evaluated for the ground motions recorded in Bucharest area is on average 3.7 times larger than the one corresponding to I_JMA. An empirical model using the earthquake magnitude and the horizontal peak ground acceleration as parameters is proposed for the evaluation of I_JMA. Finally, the computed mean annual rate of exceedance for Bucharest for a level I_JMA = 5.0 is of about 0.02, a value obtained both from observations and from a simulated Monte-Carlo earthquake catalogue.