DETECTION OF LIQUEFIED SITES USING SEISMIC GROUND MOTION RECORDS

When a large earthquake occurs, buried pipes and harbor structures often suffer from serious damages. These damages are mainly caused by large ground deformation due to soil liquefaction. Hence, it is important to detect liqu efied sites at an early stage. Many seismometers ha ve been deployed in Japan and acceleration records at liquefied sites were obtained in recent earthquakes . In this study, a method to detect soil liquefaction using acceleration records is proposed based on a dataset including records at liquefied and non-liqu efied sites. As for the records at liquefied sites, the predominant period of the horizontal components tends to be longer. On the other hand, the predominant period of the vertical component is not lengthened even at a liquefied site. To reveal these characteristics, the change of the predominan t frequency over the time was calculated from the Fourier spectra and the zero-crossing period. The o ccurrence of liquefaction is judged by setting threshold values for the JMA instrumental seismic i ntensity and the predominant frequencies for the horizontal and vertical components. KEYWORD : Detection of liquefaction, Fourier spectrum, JMA seismic intensity, Zero crossing period