基于小田原试验场地数据的不同基岩输入模型对预测地震动特征的影响研究

The Influence of Different Bedrock Input Models on Ground Motion Predictions Based on Ashigara Valley Test Site Data

随着强震台网的密布及观测记录的增加,为研究各类局部场地地震反应预测模型的合理性提供了有效的参考依据,也使利用强震记录及场地条件研究地震动特征成为可能。选取场地地质参数资料和地震记录数据齐全的日本小田原(Ashigara Valley)盲测试验场地,通过对比不同地震动输入方式及场地反应分析模型,研究地震动特征,分析现有模型的优劣。基于1990年8月5日M5.1强震事件的地表基岩记录和地下基岩地震记录,采用地下台强震记录直接输入、地表基岩台强震记录减半为基底地震动输入、地表基岩台强震记录反演为基底地震动输入作为3种基岩地震动输入。基于局部场地条件分别建立一维等效线性模型、二维黏弹性模型及二维时域等效线性化模型等工程中常用的场地数值分析模型,进行局部场地地震反应分析,预测该盲测场地的地表地震动特征,并与对应的实测强震记录结果进行对比,分析不同基岩地震动输入方式对预测地震动特征及地表土层反应谱特征的影响,重点分析地震动输入、土体非线性、场地横向不均匀性及几何与非线性特征共同作用等因素对地表地震动特征的影响,以期为地表地震动的合理预测提供参考。

With the dense network of strong earthquake stations and the continuous enrichment of observation records, it is possible to study the characteristics of ground motion by relying on the strong earthquake records of local test sites and site conditions. The rationality of various analysis models in engineering has become a key issue to improve the prediction level of ground motion. In this paper,the Ashigara Valley test site in Japan with complete geological parameter data and seismic record data is selected. Based on the M5.1strong earthquake event, different bedrock seismic input modes and site response analysis models are selected to compare and study the ground motion characteristics, and the differences of typical local site analysis models are discussed. The bedrock seismic input depends on the surface bedrock and underground bedrock seismic records, and the following three bedrock seismic input modes at the basement are adopted respectively:(1) the underground bedrock seismic records;(2) half of the strong seismic record values of the surface bedrock station;and(3) the time histories by inversion method of surface bedrock records. At the same time, based on local site conditions, the following three numerical analysis models commonly used in engineering are established respectively :(1) one-dimensional equivalent linearization;(2) two-dimensional viscoelasticity;(3) two-dimensional time-domain equivalent linearization, the seismic responses are simulated. The ground motions of this blind site are predicted and the predicted results are compared with corresponding measured strong seismic records. The differences of predicted peak values of ground motion amplification characteristics and response spectrum characteristics of surface soil layer by various analysis models are discussed. With emphasis on the influence of different bedrock seismic input, soil nonlinearity, site lateral nonuniformity and geometrical and nonlinear interaction on ground motion characteristics, it provides reference and suggestion for reasonable prediction of ground motion.