Study On The Attenuation Relationships For Horizontal Component Of Peak Gound Velocity And Peak Gound Displacement

With the rapid development of China's social economy,there are more and more medium-long period structures such as nuclear power plants,high-rise buildings,super high-rise buildings,offshore platforms,and large-span bridges.The peak ground velocity?PGV?and peak ground displacement?PGD?characterize the low-and medium-frequency information of the ground motion,which largely influence on the medium-long period structure.Therefore,the study on the attenuation relationship of PGV and PGD plays an important role in seismic hazard analysis and seismic fortification of long-period structures in different sites in different regions.In 2008 and 2014,NGA-West1 and NGA-West2have already carried out multi-parameter studies on the attenuation relationship for average horizontal component of PGA,PGV,PGD and Spectral acceleration?Sa??T?28?0.01¹0s?.However,domestic researches on the attenuation relationship of PGA and Sa usually include only magnitude and distance terms,and few studies on the attenuation relationship for PGV and PGD.Based on the strong-motion data processing,and substitutability study on observed acceleration and velocity records,this paper carries out the applicability of PGA,PGV and PGD prediction equations of NGA-West1 and NGA-West2 in the southwestern China earthquake zone.Owing to rich ground motion data in the western United States and southwestern China,we carry out the research on the attenuation relationship for the horizontal component of PGV and PGD,and establish the China's regional attenuation relationship for the horizontal component of PGV and PGD for preliminary exploration.The detail contents of research and conclusions are as follows:1.Study on the strong-motion data processing method.Aiming at the low frequency error and baseline drift existing in the acceleration records of the distant faults and small PGA,the filtering process is proposed and the high pass cut-off frequency is selected according to multiple criteria such as single inflection point source model,double angle source model,source spectrum theory and recording signal-to-noise ratio not less than 3.Aiming at the baseline drift of the near-fault strong-motion records,an improved baseline correction method combining consecutive slope ratio,displacement time-history flatness and root mean square deviation is proposed,and the coseismic displacement recorded by the GPS stations is used as a reference for verification.The effects of different correction methods on PGA,PGV,PGD and permanent displacement were analyzed.The results show that:?1?the high pass cut-off frequency is determined by multiple standards such as source model,source spectrum theory,and recording signal-to-noise ratio,which minimizes the subjective influence and provides reference processing flow and cutoff frequency selection standard for the data processing of strong earthquakes in distant faults in China.?2?The permanent displacement obtained by using the baseline correction improvement method for near-fault strong-motion records is in good agreement with the coseismic displacement observed by the GPS stations nearby.It can provide definite determination of the start time point of the strong shaking segment and the end segment as well as the number of fitting functions,which reduces the uncertainty caused by the subjective experience on the baseline correction result and improves the automation level of the baseline correction process.?3?PGA and PGV are less affected by the baseline correction methods,and different baseline correction methods have a great influence on PGD and permanent displacement.2.In order to make up for the lack of strong-motion datas in some areas,a substitutability study on observed acceleration and velocity records was conducted.Based on the observed velocity and acceleration are recorded jointly by accelerometer and speedometer at the same station of the Southern California Seismic Data Center.The distribution characteristics of velocity/displacement time history,Fourier amplitude spectrum,peak velocity/displacement ratio and peak velocity/displacement relative error based on acceleration integral and observation velocity are analyzed according to different magnitude and distance intervals.The correlation between the integral of acceleration and the observed velocity is compared and analyzed.We compare and analyze the correlation betweenPGV_ACCand PGV_VEL,the correlation betweenPGD_ACCandPGD_VEL.The results show that:?1?Based on the observed acceleration integral and the observed velocity,the velocity time histories are very consistent,and the Fourier amplitude spectrums are basically consistent at 0.1²0Hz.?2?Based on the second integral of the observed acceleration and the integral of the observed velocity,the displacement time histories are very consistent,and the Fourier amplitude spectrums are basically consistent at 0.1¹0Hz.?3?The peak velocity ratio of 93.29%and the peak displacement ratio of 87.68%are distributed in the range of 20%around 1 and both are normally distributed.?4?The correlation coefficients ofPGV_ACCCC andPGV_VEL,PGD_ACCandPGD_VELare higher than 96.03%and 96.26%,respectively,which show good correlation.?5?For areas lacking strong-motion records,the unrestricted broadband velocity records obtained from the broadband digital seismic network can be processed to obtain PGV and PGD as effective complements to the study databases for PGV and PGD attenuation relationship.3.The applicability of the NGA-West1 and NGA-West2 prediction equations in the Wenchuan,Lushan and Ludian seismic regions was studied.By using residual analysis method and analysising the PGA,PGV and PGD attenuation curves between NGA-West1,NGA-West2 model and simple modle of Wenchuan,Lushan and Ludian earthquakes under different site conditions using different finite fault models,to verify the feasibility of the NGA-West1 and NGA-West2 prediction equations are used to estimate PGA,PGV and PGD in the southwestern China earthquake areas.The effects of the selection of finite fault model and site conditions on the applicability results are analyzed.The results show that:?1?With the increase ofV_S30,the PGA,PGV and PGD attenuation curves of both the NGA-West1,NGA-West2 models and the simple model of the Wenchuan,Lushan and Ludian earthquakes,whether it is on the hanging wall or footing wall,getting closer and closer,the difference is getting smaller and smaller.?2?The NGA-West1 model generally overestimates the PGA,PGV,and PGD of the Wenchuan earthquake zone;the NGA-West2 model slightly underestimates the PGA and overestimates the PGV of the Lushan seismic zone;NGA-West2 model as a whole overestimates the PGA and PGV within the 2?27?R_rup?27?300km range of the Ludian earthquake.?3?The finite fault model given by different scholars has little difference and has little effect on the applicability results.?4?Because there is a regional difference in the attenuation relationship of ground motion parameters,it is not reliable to use the NGA-West1 and NGA-West2 models directly to estimate the PGV and PGD of medium-strong earthquakes in China.4.A multi-parameter attenuation relationship model including magnitude and distance saturation effects,magnitude-related geometric attenuation effects,fault type effects,hanging wall effects,linear and nonlinear site responses,inelastic attenuation effects,and variability of inter-events and intra-events is established.Taking the data-rich western United States as an example,the relationship of horizontal PGA,PGV and PGD in the western United States was studied.The principle and steps of the random effect regression method are analyzed.The inter-events and intra-events residuals of PGA,PGV and PGD with the independent variables parameters were analyzed.We compare WUS model with the CB08 model.The results show that:?1?The inter-event residuals and intra-residual residuals of PGA,PGV and PGD are evenly distributed between-2 and 2 along with the independent variable parameters,and no systematic trend or deviation is indicated,indicating that the predicted values of this model are basically consistent with the actual observed values,and the results are reliable.?2?The random effect regression method can eliminate the correlation between the records from the same earthquake,and for only a few recorded events,it can avoid the changes in the data within the event and the changes in the event mean caused by the bad sampling of events.The control of regression results by a large or small number of recorded earthquakes is avoided.?3?The attenuation relationship of PGA,PGV and PGD in the western United States established in this paper shows more significant magnitude and distance saturation effects in the near field of large earthquakes,eliminating the overestimation of PGA,PGV and PGD by the CB08 model in the far field of small earthquakes.5.The attenuation relationship of horizontal PGA,PGV and PGD in southwest China was studied.The method of determining finite fault model for small and medium earthquakes is studied,and the source parameters and distance parameters of each station of each earthquake are determined.The rationality of different velocity gradient extension methods to obtain the V_S30 of strong-motion stations in Yunnan and Sichuan is compared and analyzed.The feasibility of applying the multi-parameter attenuation relation model established in the previous chapter to southwest China is studied using residual analysis method.Based on the acceleration records of 2,274 major earthquakes in southwest China from 2008 to 2019,the attenuation relations of PGA,PGV and PGD in southwest China were established by using random effect regression method.The results show that:?1?The proposed method to determine the finite fault model of small and medium-sized earthquakes can effectively determine the strike,dip angle,slip Angle,size of fault failure surface,fault type,and relative position of source in the fault failure surface.?2?The borehole data of the strong motion stations in Sichuan and Yunnan are more reliable using the velocity gradient extension model of Yu and Li?2015?and Boore?2004?respectively.?3?The inter-event residuals and intra-event residuals of PGA,PGV and PGD are uniformly distributed along with the independent variable parameters around-2²,showing no systematic trend or deviation,indicating that the predicted values of PGA,PGV and PGD attenuation relations in southwest China established in this paper are basically consistent with the actual observed values,and the results are reliable.?4?In the near field of large earthquakes,more significant magnitude and distance saturation effects are shown.The feasibility of this study on the attenuation relationship of horizontal PGV and PGD is further verified.