EFFECTS OF THE DEPRESSION IN THE TOPOGRAPHY OF BEDROCK UNDERLYING BEIJING ON EARTHQUAKE GROUND MOTION

There is a belt of abnormally high seismic intensity along the line of Sanlihe-Xisi-Deshengmen in Beijing city during the Tangshan earthquake. Various hypothesis as to the cause of this abnormal belt have been suggested.Because the earthquake risk of Beijing city is not negligble and more and more highrise buildings are being erected,it might be necessary to find out the cause resulting in this belt of high seismic risk.Through detailed researches on a typical geological profile and its earthquake response by using the extended SAP 5 program,the following main results are obtained:1.It is found that a depression of the underlying bedrock to a depth of 1000-1500 meters plays a dominant role in causing the belt of abnoralty intense earthquake damage in Beijing.2.The calculated predominant periods of the response spectra at different sites above the depression are from 0.85-0.95 see.These conclusions are likely to be helpful to the earthquake-resistant design of high-rise builings in the urban area of Beijing or other similar zones.