Elasto-Plasticity Consideration of the Ground on the Large Acceleration Time Histories at Two Earthquake Observation Sites

Abstract

Large vertical acceleration of 3866 gal was recorded on the ground surface at KiK-net West-Ichinoseki (IWTH25) station during the 2008 Iwate-Miyagi Nairiku earthquake. This large UD component is strongly asymmetric with respect to the horizontal zero-axis, whereas NS and EW component are broadly symmetric. It has been found that this asymmetric waveform is able to be predicted by the elasto-plastic dynamic response analysis inputting both horizontal and vertical input wave simultaneously. Also, large acceleration was observed during the 2011 Off the Pacific Coast of Tohoku Earthquake at K-NET Tsukidate (MYG004) station. Many researchers claim that this large acceleration was caused due to the partial uplifting of the foundation of seismometer. In this paper, we showed that the dilatancy or volume change of soil can be one of the possible reasons for that large acceleration.