Development of sensor for measuring permanent displacement using servo-type velocity seismographs

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The earthquake damages of the lifeline such as buried pipelines are caused mainly by deformation of ground that is accompanied with liquefaction or landslides. It is important that the deformation of ground can be measured to estimate total damage of lifeline system at the early stage of restoration. But the sensors of ground displacement or liquefaction are not arranged in this time.Recently many servo-type velocity seismographs are arranged. As the frequency range of a servo-type seismographs is very wide, from 0.02Hz to 70Hz, the seismographs may measure the permanent displacement of the ground from the component of the low frequency range.The purpose of this study is to develop new method to estimate permanent displacement of the ground in the effective precision using servo-type seismographsAt first the response of the seismographs is simulated against the ground motion which include permanent displacement. As the result it is understood that the permanent displacement can be estimated if the seismic signal in the long period component can be removed from the record. But the influence of declination of the instruments is found to be considerably large.The method for estimating long period signals is developed using phase characteristics in short period range of the record. Group delay time is adopted to represent phase characteristics of seismic motions. We proposed the stocastic impulse train model for representing source process. It is concluded that the long period signals can be estimated to some extent from the phase characteristics of a short period component of earthquake motion.