Effects of moment magnitude, site conditions and closest distance on damping modification factors

Damping modification factors (DMF) are used to adjust response spectral values corresponding to damping 5% of critical to other damping levels. Ground motions recorded are orderly grouped according to moment magnitude, site conditions and closest distance. Near-fault motion records with closest distance closer than 10 km are not included in this paper. Based on the classification, the effects of the three seismological parameters on the median DMF are investigated. Consequently, the influence of site class reduces with increasing earthquake magnitude, and the effect of closest distance generally can be neglected with closest distance closer than 100 km except for rock sites. Except for soft soil sites, moment magnitude has a more significant effect than closest distance and site conditions, and the median DMF from acceleration spectra are most sensitive to seismological parameters. For soft soil sites, the median DMF only vary a little with moment magnitude and closest distance.

► Effects of seismological parameters on the median DMF from spectra (Sa, Sv and Sd). ► For site B–D, magnitude has most influential while DMF for Sa are most sensitive. ► Effect of site class is more obvious for small earthquakes than for large events.► Effect of distance is neglected for site Classes C–E with distance closer than 100 km.► Dependence of DMF on periods reduces with increasing magnitude for site Class B–D.