[in Japanese]

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 Recently, a few studies have considered the effect of scattering attenuation to isolate intrinsic attenuation from total attenuation while estimating attenuation in the ultrasonic laboratory measurements. Recent advances in non-destructive methods such as Magnetic Resonance Imaging (MRI) and X-ray computed-tomography (CT) allow heterogeneous microstructures of specimens to be imaged, which enables us to adequately estimate scattering attenuation. However, often, assumptions of attenuation models and methods of estimating attenuation are not fully validated. This article describes the most commonly used attenuation model expressed as an exponential decay, which leads to clarifying the assumptions of the model. Furthermore, I imply that quality factor (Q-value) which is defined as the ratio of the total energy in a system to the energy lost per cycle is a phenomenological quantity. Then, I explain the basis of attenuation estimation by giving an example of the spectral ratio method which is the most common method based on spectral ratios, where data from two receiver distances across a medium of assumed constant Q-value are selected. Dependency of attenuation results on extraction of the first arrival waveform from the observed waveform is also indicated. Finally, I emphasis on the significant influence of scattering effect on attenuation measurements and emphasizes the necessity of revisiting the theory and models of seismic scattering, especially for the case of Mie scattering regime where strong scattering could occur and full waveform modeling is required.

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 Attenuation characteristics of near-surface rock, such as “10 Hz transition” and “low Q”, were investigated based on borehole recordings of earthquake at rock site and laboratory measurements of rocks sampled near the borehole. Spectral ratios with the frequency from 1 Hz to 20 Hz using the multiple reflected S waves between different recording levels were well explained by the bi-linear frequency-dependent attenuation model considered transition frequency of 19.5 Hz. Whereas, spectral ratio with the frequency from 18 Hz to 30 Hz using the direct upgoing S wave between GL-50 m and GL-340 m were well modeled with the frequency-independent attenuation. These results clarified that the near-surface attenuation of rock was independent of frequency over about 19.5 Hz, which was consistent with the existence of “10 Hz transition”. Then we estimated the attenuation of unfractured rocks by the laboratory measurements of ultrasonic wave. From the comparison of damping factors, it was demonstrated that the attenuation from borehole recordings was “low Q” rather than the one from the laboratory measurements using unfractured rock. Furthermore, the standard deviation of heterogeneity (heterogeneity index) was determined from the borehole velocity-log, and a good relationship between heterogeneity index and attenuation was obtained. Finally, the effects of attenuation characteristics of near-surface rock and its modeling on calculated site response transfer function were also discussed.

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 We propose a new method to estimate the path-averaged Q_S-value at low-frequencies (<0.5 Hz). In this method, we measure the decay rate of the observed S-wave spectral amplitudes against the travel times; the spectral amplitudes are corrected for effects of the S-wave radiation pattern and site amplification due to the deep sedimentary layers. The corrections are done by using the theoretical S-wave spectral amplitudes calculated assuming the perfect elastic body and the appropriate source and site amplification models; the result of this method depends on accuracy of the source and site amplification models. We examine validity of this method and effects of inappropriate source and site amplification models on an estimate of the Q_S-value. Finally, we apply this method to estimate the Q_S-value within the back-arc side mantle wedge beneath Kyushu islands. The estimated Q_S-value is about 50 in the frequency range of 0.2 to 0.3 Hz.

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 Three-dimensional attenuation structure (3-D Qs) of the crust and the upper mantle in spectral domain has been determined by tomographic techniques by using strong motion recordings. At the depth of 0-30km, the pacific side tend to show High-Qs, the side of the Sea of Japan has tend to Low-Qs, and especially strong Low-Qs estimated at the volcanic areas. The Q value of the volcanic areas have a weak frequency dependence, in which intrinsic attenuation dominate. In addition, the upper crust tends to have lower Qs-value than the lower crust. Heterogeneity of Qs affect strong ground motion, and it is important to consider 3-D Qs structure to predict the ground motion. In addition, structural differences can be considered as a factor in the heterogeneous heat value Qs.

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 The evaluation of the attenuation property by using a PS-logging technique, which uses an artificial source, was reported based on the case studies. The main benefits of this method are that it is a convenient, cost effective, and highly accurate system. An artificial source is set at the surface that generates seismic waves. These waves are then recorded by the borehole receivers, which were installed in the borehole with high density. The recorded signals are analyzed and the attenuation properties of each velocity layer are calculated in detail. This method can also evaluate attenuation properties as a function of frequencies. After showing an overview of the characteristics of the attenuation properties and the analysis method of using the PS-logging technique, we then show the case studies of the Q-value investigation, which are implemented at a hard rock and soft rock site. In these case studies, we showed results which were conducted by using a Vibrator as the source. The results of the investigation show that we can acquire data with high S/N and can evaluate the attenuation properties of each velocity layer in detail. We also showed that the Q-value, which was acquired using the PS-logging technique, contains the effect of wave- scattering caused by fractures in the rock. Evaluating attenuation properties through the PS-logging technique is useful in obtaining attenuation property in detail.

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 Atmospheric muons are produced as a result of interactions between galactic primary cosmic rays and atmospheric nuclei before traveling towards the surface of the Earth in large numbers and with high frequency. Muography, a radiographic technique utilizing atmospheric muons and suitable for studying the internal structure of gigantic objects, was first conceived of more than 50 years ago. It is useful for a variety of surveying subjects. Scientists have conducted different forms of muography experiments in pyramids to search for hidden chambers, natural resource or danger assessment in mines, as well as to study other geological phenomenon. In 2006, the first successful radiographic image depicting the unseen structures within a volcano was obtained. Based on these results, the technique has been applied to other targets and has expanded in its capabilities. For instance, there are now newly designed systems that allow researchers to create visualizations of inaccessible sections of industrial plants. This paper will not discuss in detail the results of muography experiments from 2006-2008 since these are readily available from other sources. Instead we will briefly review the history of muography in order to understand the challenges and then focus on the present and future state of muography by discussing the newest observation results and techniques.

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