To realistically assess the seismic risk relating to built infrastructures in Hong Kong and in the neighbouring coastal cities of southern Guangdong province, it is necessary to predict ground shaking induced by different earthquake scenarios with good accuracy. A companion paper has described the modelling of the spatial and temporal distribution of the diffused seismic activities in the region, based on the newlydeveloped `Expanding Circular Disc' (ECD) method. Representative Magnitude±Distance (M±R) combinations for both near-®eld and far-®eld earthquakes (in relation to Hong Kong) have been derived using the ECD method. The present paper describes the modelling of the response spectrum on rock sites associated with the predicted M±R combinations, using the Component Attenuation Model (CAM) that was also developed recently by the authors, based on stochastic simulations of the seismological model. The signi®cant effects of soil resonance on the response spectrum are described in a separate publication.
The accuracy of CAM in modelling ground motion properties on rock sites has been tested here by comparisons with (i) strong motions recorded in Taiwan and South China from the 1999 `Chi-Chi' earthquake in Taiwan (M 7.6), (ii) motions recorded in South China from another earthquake occurring in the southern Taiwan Strait in the same year (M 5.1), and (iii) historical seismic intensity data obtained within South China. The overall capability of CAM in modelling both near-®eld and far-®eld attenuation has been shown to be unmatched by existing empirical models. Results of the comparison studies con®rm the accuracy of CAM, particularly within an epicentral distance of 300±400 km.
This study shows that the developed serviceability response spectra (i.e. at short return periods) are controlled mainly by the earthquake recurrence behaviour of major distant seismic sources. In contrast, the ultimate response spectra (i.e. at long return periods) relate to events with magnitudes close to the maximum credible earthquake (MCE) limit, the effect of which may also be represented by the Characteristic Response Spectrum (CRS). Both types of earthquake scenario can be signi®cantly affected by the regional crustal properties. The proposed response spectrum envelopes have been compared with previously developed recommendations, and a critical review has been conducted. The intrinsic advantages of the ECD±CAM modelling approach have been highlighted, emphasising its directness and transparency when compared with the more complex process required to implement traditional Probabilistic Seismic Hazard Assessment (PSHA).