Response spectrum modelling for rock sites in low and moderate seismicity regions combining velocity, displacement and acceleration predictions

Seismic hazard modelling for regions of low and moderate seismicity is ofte n hampered by the lack of indigenous strong motion data. Thus, empirical at tenuation models developed for analogous 'data rich' seismic regions have t ypically been used as the basis for defining the ground motion attenuation properties of the subject region. Alternatively, limited data recorded from small tremors, or aftershocks, have been used to extrapolate the attenuati on relationships of potentially destructive but infrequent, large magnitude events. However, as explained and demonstrated in this paper, both approac hes are prone to error in the absence of a rational and viable analytical f ramework to support their application. Addressing this, the methodology int roduced herein combines the component attenuation model (CAM) (developed in the companion paper (Earthquake Engng Struct. Dyn. 2000; 29:1457-1489) wit h observations on local isolated earthquake events, to determine representa tive design response spectra for both force- and displacement-based seismic applications. In CAM, the acceleration and displacement response spectra may be construct ed very conveniently, and with reasonable accuracy, using simplified expres sions for the spectrum corner periods and the response spectral velocity pa rameter, for regions of different geological conditions. The comparison of the response spectra determined by CAM with similar response spectra descri bed by numerous well known empirical models (derived in data rich high seis micity regions) provide very useful indications of the credibility and adva ntages, as well as the limitations, of CAM. The implied increasing stress d rop with increasing moment magnitude is a significant observation from the comparative study.