Intensity attenuation relationship for the South China region and comparison with the component attenuation model

The paper utilises seismic intensity information from historical (pre-instrumental) earthquakes in the South China region, to evaluate the mean attenuation relations. The formulation of these attenuation relations accounts for the seismic waveguide effects, in delineating three parts of the geometrical attenuation relationship. The derived relations are then compared with the intensity attenuation predictions implied by the newly developed component attenuation model (CAM), which is considered to be particularly applicable in regions of low. or moderate seismicity that typically have limited earthquake records. Recognising that the observed intensities from historical earthquake events may implicitly incorporate some site effects, the incremental difference between the two models (between 0 and 1 unit of intensity) is found to be accountable in terms of average regional site effects arising due to the near-surface geology or soils. It is therefore concluded that the CAM model gives remarkably accurate predictions of ground motion and implied seismic intensity across a large range of earthquake magnitudes and at site-source distances ranging up to 500 km. The larger site-source distances, representing far field and very far field-events, are particularly important in the South China region, including Hong Kong (HK), due to the large disparity in seismic activity rates in the region surrounding HK (which is rather seismically stable) and at distances > 300 km from HK, where some relatively active seismic zones exist. (C) 2002 Elsevier Science Ltd. All rights reserved.