A Rapid Conjecture Method Of Ground Motion Waveform Field Using Strong Motion Records

After a destructive earthquake occurs,the rapid estimation of the ground motion field is an essential part of disaster prevention and mitigation tasks such as disaster research and judgment,situational awareness,and emergency rescue.With the gradual progress of the “National Seismic Intensity Rapid Reporting and Earthquake Early Warning Project” project,the rapid output of post-earthquake ground motion parameter fields and instrumental seismic intensity fields has been achieved,providing crucial technical support for post-earthquake emergency work.Compared with the ground motion parameters,the ground motion time history(waveform)contains more abundant and valuable ground motion information.The existing ground motion simulation methods involving the source,path,and site have many input parameters and are complicated and time-consuming.It is still difficult to meet the emergency timeliness needs minutes after the earthquake.Aiming at the above-mentioned critical problems and facing the post-earthquake emergency needs,this paper proposes a rapid conjecture method of ground motion waveform field using measured strong motion records,which aims to quickly generate waveform fields on the time scale from minutes to hours after the earthquake,thereby providing reasonable ground motion input for post-earthquake situational awareness,disaster scenario simulation,scenario construction,and urban resilience assessment,and outputting more detailed instrumental seismic intensity field and the seismic intensity map quickly.The works were carried out as follows:(1)A ground motion amplitude spectrum model was proposed based on the Inverse-Distance-Weight interpolation method.This model avoided the problems existing in the traditional model,such as multi-parameter input requirements,and can quickly conjecture the ground motion amplitude spectrum of the target field after the earthquake.Moreover,a fast selection method of interpolation sample stations based on the Delaunay triangulation algorithm was also proposed,which avoided the problems of uncertainty,randomness and time-consuming in the process of manual selection of sample stations.It can quickly provide scientific and reasonable sample stations for the interpolation of the ground motion amplitude spectrum of the target site.The model’s reliability was verified by using Ki K-net seismic data from Japan.The results show that the amplitude spectrum obtained by interpolation had a good consistency with the measured record in terms of amplitude value,spectrum shape,and predominant frequency.(2)The phase characteristics of ground motions were studied,and two commonly used phase spectrum models based on phase difference and those based on equivalent group velocity were compared.The results show that the phase spectrum model based on the equivalent group velocity can better reflect the time-space propagation law of seismic waves.This model was selected to provide phase information for the conjecture of ground motion.(3)A method for rapidly conjecturing broadband ground motion using measured strong motion records were developed.The method applied the seismic amplitude spectrum model proposed in this paper and the current phase spectrum model based on the equivalent group velocity.The rationality and reliability were verified by the measured records of the Ki K-net station in Japan,and the influence of the site effect on the ground motion conjecture results was studied.The results show a certain degree of difference between the conjectured results and the measured ones in the corresponding frequency band regarding waveform and ground motion characteristics of lowfrequency ground motions(0.1～1Hz).However,the PGA and the arrival time of the seismic phase are close.Regarding the waveform,PGA,phase arrival time,and ground motion characteristics,the conjectured results had good similarity and consistency with the measured records in broadband ground motion(0.1～25 Hz).In addition,the conjectured records can better reflect the site characteristics at the target site and the frequency-dependent characteristics of ground motions.The ground motion amplitude spectrum,considering the site effect,had better consistency with the measured record,but the ground motion time history and other related characteristics were still different from the measured record,and the consistency did not improve.(4)A method was proposed to determine the main contribution frequency band of PGA by shifting the band-pass filter’s high cut-off frequency in the band-pass filtering process of the acceleration recording.It was used to analyze the frequency dependence of broadband ground motion.(5)The scope of application of the method in this paper was expanded,and an alternative plan for interpolating sample stations in a region with sparse station density was given.The demonstration application of the method for the rapid conjecture of ground motion waveform field was carried out using domestic multiple earthquake examples.The obtained waveform field was applied to the generation of instrument seismic intensity field and seismic intensity map.