论文部分内容阅读
由于难以很确切地将局部场地反应与其他较显著的效应区分开来,因此非线性场地反应的研究存在着实际困难。我们在洛杉矶盆地选择了一个沉积层场地LF6,它具有如下特点:(1)与其他台站相比,它可利用最近的参考基岩场地,以对局部场地放大作用进行准确估计;(2)它可以揭示近地表处清晰的共振现象。我们认为:在确认可能的非线性方面,这种情况呈现出最小的不确切性。将北岭地震、1987年惠蒂尔纳罗斯地震和北岭余震期间的场地反应进行了比较。该台站的记录显示出,在所采用的全部17个地震中,对较大及较小幅值的震动,其基本共振频率有所变化。北岭地震期间的总剪切模量变化是惠蒂尔纳罗斯地震的1.3～1.4倍,并且是余震的1.7倍。对于盆地内其他非线性反应特征难以描述的场地,这一结果将对场地反应的估计起到指导性作用。
Since it is difficult to distinguish local field reactions from other more significant effects, there are practical difficulties in the study of nonlinear field reactions. We chose LF6 in the Los Angeles Basin as a sediment site, which has the following characteristics: (1) It can make use of the nearest reference bedrock site to accurately estimate the local site amplification compared with other stations; (2) It reveals a clear resonance near the surface. We think this situation presents the least uncertainty in terms of identifying possible non-linearities. Field responses to the Northridge earthquake, the Whittier Niros 1987, and the Northridge aftershocks were compared. The station's record shows that for all 17 earthquakes used, the fundamental resonance frequency varies for larger and smaller amplitudes. The change in the total shear modulus during the Northling earthquake is 1.3-1.4 times that of the Whittuna Ross Earthquake and 1.7 times that of aftershocks. This result will play an instructive role in the estimation of site response to other sites in the basin that are otherwise difficult to characterize.