Ground Motion Prediction Model For Shallow Crustal And Upper Mantle Earthquakes In Subduction Zones Using A Complex Path Model

A ground motion prediction equation(GMPE)is an important part of earthquake engineering and can be used in seismic hazard analysis for an engineering site.Many GMPEs have been developed for different regions around the world and various types of earthquakes.At moment,nearly all GMPEs model the path effect of earthquakes by using a simple geometric attenuation function with or without magnitude dependent coefficient,however,this type of geometric attenuation function cannot model the effect of the deep-crust wave-reflection,such as the Moho reflection,and reflections and constructive interference of other complex propagation paths in subduction zones.Some studies suggest that neglecting this type of path effect modeling would result in considerable errors in both the median prediction and the standard deviations leading to the reduced model goodness-of-fit and erroneous estimates of the ground-motion parameters,such as the design spectrum.Many GMPEs for the horizontal component have been developed and relatively few for the vertical component,however many earthquake field investigations and research results suggest that some structures,such as longspan bridges,buildings with large internal spacings,and a cantilever structures are susceptible to vertical ground motions,leading to severe structural damages by large vertical ground motions.Many design codes use a constant to scale the horizontal spectrum to obtain the vertical design spectrum and this method is not reliable and improvement is due.This study used 5957 strong-motion records from 70 shallow crustal events and 47 uppermantle events obtained by Ki K-net and K-NET networks in Japan and a GMPE with a single geometric attenuation function was established first.Extensive residual analyses were carried out to introduce appropriate multi-segmented geometric attenuation and GMPEs using the complex path model were developed for the shallow crustal and upper mantle earthquakes.The main results are listed below,(1)Developed GMPEs with simple geometric attenuation for the horizontal and vertical ground motions first and the GMPEs for the horizontal component account for the nonlinear site response that is not necessary for the vertical component.Residual analysis suggested the geometric attenuation rate varies in different distance ranges and the variation of the attenuation rates and distance breakpoints are similar to but not identical to those of the Fourier spectrum attenuation model.This means that the Moho reflection characteristics can be observed in the attenuation of the response spectrum and the effect can be incorporated into a GMPE;(2)According to the locations of the strong-motion stations,the within-event residuals for the shallow crustal records were divided into several regions and the residual distributions from these regions suggest that the effect of Moho reflection can be observed in most parts of Japan.The analysis of within-event residuals from the earthquakes below the Moho discontinuity also suggested that the effects of the Moho reflection can be observed in these deep earthquakes;(3)A GMPE accounting for complex path effect for the horizontal component was developed for shallow crustal events using a multi-segmented geometric attenuation function with three distance breakpoints of 70,130,and 220 km.The geometric attenuation function for the upper mantle events has two distance breakpoints at 90 and 150 km.The use of a segmented geometric attenuation function leads to a significant increase in the maximum likelihood with a maximum increase of 40.4.The distributions of these residuals versus distance are not biased and the standard deviations are either reduced or similar to those without the using the complex path effect model;(4)A GMPE using segmented geometric attenuation functions for the vertical component was also developed.The distance breakpoints from the model for the horizontal components were used for the vertical component and only an elastic site effect model was necessary.The increase in the maximum log-likelihood,the improved the residual distribution,and the standard deviations suggest that the segmented attenuation function improved model performance;China is on the boundary of several tectonic plates and the geological and the tectonic setting is complex with Taiwan having two subducting systems.Also,some studies suggest that the attenuation characteristic of the ground motions in the west and southwest of China are similar to those of the shallow crustal events in Japan.This means that the results from this study may be used as a reference or applied to the seismic hazard analysis,seismic microzonation,or seismic design of structures in China with or without modifications.