Attenuation of earthquake ground motion in Japan including deep focus events

Abstract

Abstract New attenuation equations for peak ground acceleration and velocity for Japan are developed. The equations are derived using extensive data recorded by the new JMA-87-type accelerometers, which do not require instrumental corrections that the older SMAC-type accelerometers do. Earthquakes with depths up to 200 km are used to make the equation applicable to subduction zone regions, which are common in Japan. Effects of depth and local site on the attenuation are considered simultaneously with the distance dependence and magnitude dependence using a two-stage regression procedure to separate the magnitude dependence from the distance dependence. Since the resulting normal equations become singular, an iterative partial regression algorithm is proposed. It is found that for the same magnitude and distance, peak ground motion increases as depth increases. The variation of the station coefficients with respect to the corresponding soil-type classification is quite wide. The station coefficients for the peak ground acceleration are found to be weakly correlated with the general soil classification, while a stronger correlation was found for the peak ground velocity. The resulting attenuation relations are given by log10PGA=0.206+0.477MJ−log10r−0.00144r−0.00144r+0.00311h+cia,log10PGV=−1.769+0.628MJ−log10r−0.00130r−0.00144r+0.00222h+civ, where PGA (cm/sec2) and PGV (cm/sec) are the larger of the peak accelerations and velocities from two horizontal components, MJ is the JMA magnitude, r is the closest distance to the fault rupture, h is the depth, and ci is the station coefficient of the recording station. The mean of the coefficients of the JMA stations is given by ci = 0.