Spectrum representation of strong motion duration has been proposed using total threshold intervals of velocity response envelope calculated for viscously-damped single-degree-of-freedom oscillator of various natural periods.In addition to uniform thresholds in terms of velocity response, frequency-dependent threshold functions defined for various performance limits under strong motion are also applied. Examples of spectral representation are shown using two strong motions representative of a shallow crustal earthquake and a mega-thrust interplate earthquake. Examples of map representation are shown using approximately 700 strong motion records obtained in the 2011 off the Pacific coast of Tohoku Earthquake. It has been shown that the proposed method provides a convenient measure of frequency-dependent duration and the influence of strong shaking on various phenomena including structural response and human behavior.

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We studied characteristics of strong ground motions from the Off-Sanriku outer-rise earthquakes; these earthquakes are activated after the 2011 Tohoku earthquake (Mw 9.0). First, we calculated pseudo velocity responses for five outer-rise earthquakes (Mw 6.0-7.6) and compared them with the attenuation formulae which were constructed for the intraslab earthquake. In spite of outer-rise's data being over the distance range of these formulae, the extrapolated formulae generally explained the attenuation relations of these observed data. However, there were considerable residuals between the observed and predicted values. These residuals result from the site and source effects, because the previous attenuation formulae were constructed based on many site's strong motion records from many earthquakes occurring at various source areas. Second, in order to overcome the weakness of the previous attenuation equations, we proposed empirical ground motion prediction equations for a single site; we named these equations “Single-Site GMPE (SS-GMPE)”. Our data for regression analysis were strong motion records at a single observation site from the five outer-rise earthquakes occurring at the narrow source area with the radius of about100km. We carried out a regression analysis with respect to Mw for each site assuming the previously estimated internal attenuation for intraslab earthquakes. The earthquake source, propagation path and site effects were well incorporated into these equations, and as a result, the residuals between the observed and predicted values were considerably decreased. Finally, we applied the SS-GMPE to earthquakes not used in the regression analysis and found the good correspondence of predicted and observed spectra.

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The objective of this study is to investigate in detail the characteristics of strong ground motions separated from Fourier spectra using the observed data by K-NET, KiK-net, and JMA seismic intensity meter Network in Japan.We found that our Q models are comparable to those of previous studies, and that Q models are dependent on regions in and around Japan. Brune (1970)’s stress drop has a magnitude dependence in between mainshocks and aftershocks (or smaller events in general), and short-period levels A are in good agreement with those of Satoh (2003), but not in good agreement with that of Dan et al. (2001) for crustal earthquakes. We also found that site amplifications are stable regardless of the observed period with some possibility of directional dependence, and that site amplification for a site has a standard deviation around 0.2-0.3 in the target frequency range.

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In this study, by means of simulation of strong ground motions based on the pseudo point-source model, which is one of the source models for strong ground motions during the 2011 off the Pacific coast of Tohoku earthquake, we investigate the degree of agreement between the observed and synthetic Fourier spectra in the Kanto Region. The results indicate that, to achieve good agreement between the observed and synthetic Fourier spectra, careful consideration of the path effect is required. We used a revised path model in which following two effects are considered: (1) the geometrical spreading term inversely proportional to the square root of the distance at large distances, (2) the lower bound of the Q value at lower frequencies. By using a revised path model with these effects, a good agreement was achieved between the observed and synthetic Fourier spectra in the Kanto Region.

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Microtremor array measurements have been carried out to estimate the detailed S-wave velocity structures of shallow soil structures in the Tachikawa-fault zone. Array measurements of vertical microtremors were used to retrieve phase velocity of Rayleigh wave. Through the inversion of the phase velocities, we have estimated the S-wave velocity structures. The shallow S-wave velocity structures have significant variation in the vicinity of the northern part of Tachikawa-fault. Depths to the engineering bedrock in the southwest part of the fault are deeper than those of the northeastern part of the fault. The southern part of the fault zone exhibits a complex variety in the S-wave velocity structures, with the variety of amplification in the area. The AVS30 has the significant relationship with amplification such that high AVS30 makes small amplification and short dominant period. The variety of the structure expected from existing information was also found in the S-wave velocity structures estimated in this study. However, AVS30 in this study was relatively higher than that from the geomorphological classification. It generates the amplification smaller in this study and shortens the dominant period than that estimated from geomorphological classification. However, since this characteristic can be held only in Tachikawa-fault zone, it is important to predict the strong motion characteristics based on the precise investigation of the S-wave velocity in the target area.

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The Geographic Information System is useful tool for disaster responses. In this study, we proposed two requirements (1) International standard interface for requesting GIS data (Web Map Service) and (2) web-based GIS. In the 2011 off the Pacific Coast of Tohoku Earthquake, authors supported disaster volunteer center in Miyagi prefecture and local governmental disaster responses in a local government. The “e-Community Map” which have the two requirements was used. Through the case study, usefulness of the two requirements was indicated.

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We generate stochastic Green's functions considering surface waves and scattering waves using strong motion records in the Kanto district of moderate-sized intraplate earthquakes along the Sagami Trough. The spectral ratios of the later time windows to S-wave windows are modeled by a regression equation. The envelope of S-wave windows are modeled based on scattering theory for S-wave and that of the later time windows are modeled based on the scattering theory for both body waves and Rayleigh waves. Generated stochastic Green's functions simulate observed records much better than previous ones in which only direct S-waves are considered.

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