A Preliminary Attenuation Relation of Long-period Ground Motion in Sichuan Area

摘要

The goal of the present study is to derive a long-period (up to 10s) attenuation relationship of horizontal acceleration response spectrum for Sichuanarea based on the strong ground-motion records from the Wenchuan earthquake and its aftershocks.Long-period spectrum is very important for the seismic design of high-rise buildings and long-span bridges with long natural periods.Because there werefew strong-motion records obtained in China,and the number of records decreases with increasing spectral periodover about 3s,long-period spectrum attenuation models are much more difficult to deyelop.Theattenuation relationship of ground motions used in the past design code wasthe modified attenuation models for the western part of the United States based on the relationships between the seismic intensity attenuations in the two regions.During the 2008Wenchuan earthquake and its aftershocks,a large number of strong-motion records were obtained.It is now possible to develop a long-period attenuation relationship for the horizontal acceleration response spectrum in the Sichuan province.Firstly,recordsfrom the Wenchuan earthquake and its aftershocks were processed,the momentmagnitude,focal mechanisms,accurate locations,distance from source to stations,and average shear-wave velocity of recording stations were collected.Secondly,a study was carried out to compare the recorded spectra with a number of modem attenuation relationships.We found that the shallow crustal model (Zhao et al.,2006) attenuation relationship fitted the data acceptably well,but generally larger than the records at moderate and long spectral periods.Finally,we adopted the model coefficients in the Zhaomodel that constrain the near source model prediction and developed an attenuation relationship for Sichuan for periods up to 10s.The attenuation relationship developed in the present study is generally better than the Zhao model at long periods.