| The ground motion duration is one of the three elements that characterize the characteristics of ground shaking.The ground motion duration,especially the strong ground motion duration,has an important influence on structural damage and the inducement of strong earthquake geological hazards.Duration is a key parameter in the ground motion simulation method of stochastic point source and stochastic finite fault,and artificial seismic wave synthesis method,which is an important index to evaluate the accuracy and reliability of simulated ground motion or synthesis of artificial seismic waves.Most of the studies have been conducted for horizontal ground shaking motion duration,but there are fewer studies focusing on the effect of basin sites on duration and vertical ground motion duration.In this thesis,we firstly analyze the factors influencing the duration,secondly analyze the influence of basin effect on the duration and the difference between horizontal and vertical ground motion based on the ground motion data of Kanto basin,and finally analyze the applicability of the duration prediction equations based on the NGA-West database and the Japanese crustal ground motion database to predict the duration of typical strong earthquakes in the Sichuan-Yunnan region.A preliminary analysis of the regional characteristics of ground motion duration in the Sichuan-Yunnan region is presented.The specific work includes:Influencing factors and laws of duration were summarized from prediction equations characterizing the ground motion duration properties of the NGA-West database(KS06,BSA09,LG14,AS16,DW17)and the prediction equation characterizing the ground motion duration properties of Japan(BRG21):The significant duration increases with the fault rupture distance and moment magnitude and decreases with VS30.For the near-field case of large earthquakes,the significant duration is mainly influenced by the source term and increases with the magnitude.In the far-field case of minor earthquakes,the significant duration is mainly influenced by the path term.There are regional differences between the duration characteristics of the NGA-West database and the Japanese database,especially when the fault rupture distance is less than 20 km.The perceptions of the selected duration prediction equations are inconsistent and qualitatively different with respect to the effect of basin sites on ground motion duration.A significant duration DS5-95 database was constructed utilizing 162 shallow crustal earthquakes recorded at regional strong-motion stations in the Kanto Basin from 1998 to 2021.Based on the residual analysis method and the duration ground motion prediction equations of KS06,AS 16 and BRG21,we analyzed the influence of basin effect on ground motion significant duration and established several basin effect models,and also compared the difference between vertical and horizontal significant duration.The results show that for the case of comparable fault distance and site VS30,the significant duration of in-basin station is generally larger than the out-of-basin station duration,and all three prediction equations can achieve a reasonable estimation of the horizontal DS5-95 for the out-basin station.The vertical significant duration as a whole is larger than the horizontal significant duration,and none of the three prediction equations can be directly applied to the estimation of vertical earthquake ground motion duration.Except for BRG21,the basin effect models in KS06 and AS 16 prediction equations significantly underestimated the amplification effect of deep sedimentary layers in the basin on the significant duration.A basin effect model of significant duration with Z2.5 as the independent variable was established,and compared with the previous model with δZ1 as the independent variable,the new model more reasonably reproduces the continuous increase of basin duration as the sedimentary thickness of the basin becomes larger.Taking the Lushan mainshock and Wenchuan mainshock as examples,the applicability of KS06,AS 16,BRG21 and XW18 to the duration prediction of the Lushan and Wenchuan mainshock was evaluated in focus by combining the residual analysis method.The results show that all four selected duration prediction equations can achieve the prediction of the horizontal duration of the Lushan mainshock,among which XW18 has the best prediction,and the vertical duration of the Lushan mainshock is larger than the horizontal duration.Wenchuan mainshock has a large ground shaking significant duration due to the long fault rupture,and all the four duration prediction equations are not suitable for predicting the significant duration of the Wenchuan mainshock.The distribution of the three-component significant duration residuals for the Wenchuan mainshock is approximate and does not correlate well with the form of the specific prediction equation. |
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