MOTION INDUCED BY DISTANT EARTHQUAKES: ESTIMATED GROUND SHAKING IN HONG KONG

摘要

To realistically assess the seismic risk of the built infrastructures in Hong Kong and in the neighbouring coastal cities of southern Guangdong, it is necessary to predict ground shaking induced by different earthquake scenarios with good accuracy. The predictive models used for the assessment must account for the seismicity (level of seismic activity), seismo-tectonic properties (style of faulting and slip rates affecting stress-drop) and average geological conditions (crustal structure affecting wave attenuation properties) of the region. Key ground motion parameters (peak response spectral velocity, displacement and acceleration) have been predicted in this paper for the critical earthquake scenarios comprising (ⅰ) moderately large magnitude (M) but rare events occurring at medium site-source distances (R < 50 km), and (ⅱ) very large magnitude (M > 7.0) events which occur more frequently in the wider South China region, but at larger distances R (> 200 km). The Magnitude-Distance (M-R) combinations for both types of design earthquake (referred herein as near-field and far-field earthquakes, respectively) have been determined for Return Periods ranging between 70 and 2,500 years, based on the spatial and temporal distribution of historical and recent instrumental earthquake events. The bedrock motion properties for each of these M-R combinations have been determined by the Component Attenuation Model (CAM) developed recently by the authors based on stochastic simulations of a seismological model. It is demonstrated in this study that earthquake ground motions generated by far-field events are particularly important for short Return Period (70-500 years) considerations and for long period structures including high-rise buildings and long-span bridges. Conventional models based on probabilistic seismic hazard analysis and assuming ground motion attenuation relationships from so-called analogous seismic regions, fail to capture the important features of the long period (displacement) demand, for relatively short return period design earthquake events. The additional effects of soil resonance are dealt with in a companion paper (Chandler et al., 2000).