We review studies of long-period ground motion and surveys of deep subsurface structure in Hokkaido. The long-period ground motion studies have been begun by using JMA strong-motion records. The records demonstrated excitation of basin surface waves at large plains such as the Tokachi and Yufutsu plains; basin-induced surface waves from nearby intermediate-depth events and basin-transduced surface waves from regional shallow events. A seismic array observation using a digital recorder elucidated wave types and propagation characteristics of the basin-induced and basin-transduced surface waves in the Tokachi plain. The deep subsurface structural surveys have been begun to explore oil and natural gas reservoirs in and around Hokkaido; a few surveys have been done to clarify the nature of long-period ground motion. Recently the National Research Institute for Earth Science and Disaster Prevention (NIED) constructed a three-dimensional subsurface structural model of Hokkaido by combining all the previous surveys. Finally we briefly review studies of long-period ground motion obtained by the dense strong-motion network, e.g., K-NET and KiK-net, during the 2003 Tokachi-oki earthquake (M8.0).

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 We examined the average predominant period of seismograms observed at the strong ground motion observation stations, maintained by CEORKA (Committee of Earthquake Observation and Research in the Kansai Area), in the Osaka basin for 7 earthquakes (M_J5.4-7.4), which occurred in Western Japan.
We also derived the predominant period of fundamental-mode Love and Rayleigh waves from their dispersion curves, calculated for the 1-D velocity structure models extracted from the Osaka basin model. The observed predominant periods show good agreement with the calculated predominant periods smoothed by spatial windows with radii of a wavelength for Love waves as well as Rayleigh waves. Based on this result, we made a predominant-period map of the Osaka basin. This map provides useful information about earthquake resistant of high-rise buildings.
We find simple linear relationships between the calculated predominant periods of the surface waves (Love and Rayleigh waves) and the sediment thickness beneath sites. Specifically, the predominant periods in unit of second for Love waves are 5 times the sediment thickness in unit of km and those for Rayleigh waves are 2 times. However, this relationship is bounded at periods of 6-8 s for Love waves.

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 Strong ground motions observed in the Kanto basin during the Tonankai Mw8.1 earthquake in 1944 have been estimated from historical seismographs at Togane, Otemachi (Tokyo) and Yokohama. The reproduced seismograms demonstrate large (>10 cm) and long-time (>600 s) shaking of long-period ground motions at a dominant period of about 7 to 12 s in the center of Tokyo during the Tonankai earthquake. Such long-period signals are strongly radiating from large earthquake and then amplified significantly in thick sediments of the Kanto basin overlying rigid bedrock. The velocity response spectrum of strong ground motions shows large and sharp peaks at a dominant period of about 12 s and amplitude of about 60 cm/s at Togane and about 30 cm/s at Yokohama. A large velocity response is found at Otemachi in the period of 8 s with amplitude of about 25 cm/s. These amplitude levels are roughly 2-2.5 times larger than those observed in Tokyo during the SE Off Kii Peninsula (Mw7.4) earthquake in 2004.

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 The 2003 Tokachi-oki earthquake (Mw=8.0) caused the severe damage to oil storage tanks such as tank fires, submergence of floating roof, and overflow of large amount of oil, due to large liquid sloshing more than 3 m excited by the long-period strong ground motions. According to the Japan fire service law for the maximum sloshing wave height at that time, the velocity response spectrum at a period of sloshing was about 1 m/s. Considering both predicted spectra at petroleum industrial complexes for earthquakes with maximum expected magnitude in each seismotectonic zone and damage pattern of oil storage tanks at Tomakomai, we proposed design spectra for liquid sloshing of oil storage tank in Japan by introducing the correction coefficients as a function of period and source region. The design spectra were adopted in the revised Japan fire service law enforced on April 2005.

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 The development of the IP (induced polarization) measurement technique used inside a tunnel is required in order to estimate the subsurface resistivity and chargeability structures with high precision. One of the largest problems in an IP measurement inside a tunnel is how nonpolarizable electrodes for potential measurements are fixed on a hard base rock of the tunnel wall. This problem is conquered by pasting up the nonpolarizable electrodes on the base rock with the plaster which is mixed with the same salts used for the electrodes. By using this contact method of nonpolarizable electrodes, highly precise two-dimensional IP measurements were carried out on tunnel walls of a sericite deposit. Sericite veins and hydrothermally altered rocks along the tunnel walls were clearly detected by normalized chargeability, which is chargeability normalized by resistivity.

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 The frequency-domain helicopter-borne electromagnetic (HEM) method is the most suited for resistivity mapping in very large areas. Another advantage of HEM survey is to provide information that allows for 3-D quantitative interpretation of the resistivity distribution. However, in many cases, the information contained in the multi-frequency data is not fully utilized, since conventional approaches to interpreting HEM data are based on the apparent resistivity and 1-D inversion. In this paper, we present the results of applying the 2-D or 3-D inversion method using the finite-difference modeling to two synthetic HEM data sets. The examples indicate that 2-D and 3-D inversions give more accurate representations of the true structures than the analysis of apparent resistivity and the 1-D inversion. The computing time for 3-D inversion is about 20 hours on PC for a survey area including three 1-km flight lines separated by 100 m. This level of efficiency is achieved by taking advantage of the feature unique to the HEM method that the transmitter and receiver coils can be assumed to be superposed, which results in eliminating the pseudo-forward modeling needed to compute the sensitivity matrix. For actual surveys covering much larger areas, it is recommended that the entire survey area should be divided into sub-areas so that 3-D inversion is feasible for each sub-data set on PC.

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 Partial derivatives of surface wave phase velocity with respect to layer parameters, such as P-wave velocity and S-wave velocity, are the Jacobians of the linearlized least-squares scheme for the inversion of phase velocities. They can be expressed by integrals with Frechet integral kernels computed in terms of eigenfunctions. But in most inversion applications, the Jacobians are computed by finite difference approximation. This paper proposes an accurate and efficient method based on the Haskell matrix method. The ratio of the speed of the new method to that of the finite difference method is estimated to be proportional to the number of layers.

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