Evaluation of the Ground Attenuation Property by using a PS-Logging Method at the Site of a Nuclear Power Station

Abstract

In the seismic design of nuclear power reactor facilities, it is important to investigate the underground structure in detail and to construct a precise underground structure model from the viewpoint of formulating earthquake ground motion for seismic design. Since the attenuation property, which is one of the important parameters of an underground structure model, is closely connected to the amplification of an earthquake ground motion, it is necessary to estimate more reliable attenuation properties based on analysis using earthquakes and investigations using geophysical investigation techniques. This paper shows case studies of a Q-value investigation, which were implemented at the site of a nuclear power station using the PS-logging technique. An artificial source was set at the surface that generates seismic waves. These waves were then recorded by borehole receivers, which were installed in the borehole with high density. The recorded signals were analyzed and the attenuation properties of each velocity layer were calculated in detail. This technique has received great attention recently because it can also evaluate attenuation properties as a function of frequencies with convenient methods. A wellbore was drilled at the site of the nuclear power station before implementing a geophysical investigation that resulted in the evaluation of an attenuation property with high resolution just beneath the site. This result, which contributed to the construction of the precise underground structure model around the site, shows the applicability of the PS-logging technique for investigating attenuation properties.