In this study, we evaluate an acceleration Fourier and response spectra at Ichihasama and Koromogawa seismic intensity observation sites which observed JMA seismic intensity of 6 upper but seismic waveform records don't exist during the Iwate-Miyagi Nairiku earthquake in 2008. Firstly, formula to evaluate acceleration Fourier and response spectra are developed using peak ground acceleration, JMA seismic intensity and predominant period of earthquake spectra based on records obtained from crustal earthquakes with Magnitude of 6 to 7. Acceleration Fourier and response spectra are evaluated for another local government site which are not chosen for development of the formula. The evaluated values mostly agree with the observed ones. Finally, acceleration Fourier and response spectra are evaluated for Ichihasama and Koromogawa observation sites. It is clarified that short period below 1 second was predominated in the evaluated spectra.

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During the 2008 Iwate-Miyagi Nairiku Earthquake, long period ground motion with a period of three to four second is observed in Senboku plain, Miyagi prefecture, Japan. In this paper, to characterize these ground motions, following points are studied. At first, we compare these motions and past records those abound in the long-period component using Fourier spectra. Spectral amplitudes of these event motions are almost coincident with those of past records. And stability of peak frequency at K-NET MYG006 station is studied. The result shows that predominant frequency of each event is almost the same. Finally, propagation direction is studied. Results come from this study indicate that long period ground motion is comprised of surface wave excited by deep plain structure.

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We performed temporary strong motion observation in the source region of the 2008 Iwate-Miyagi Nairiku earthquake. Based on aftershock records at the temporary stations and K-NET/KiK-net stations, we applied spectral inversion to estimate source, propagation path, and site amplification effects. The estimates of stress drop for the aftershocks are within a range of 0.1-2 MPa. Spatial pattern of stress drop was seen; approximately 1 MPa near the large slip region and 0.5 MPa or less at the northern and southern edges of the fault plane. Site amplification factors at 0.5-1 Hz are 1-3 times for the near-source stations and 0.8-2 times for stations on the east-southeastern side of IWTH26. On the other hand, site amplification factors at 1-7 Hz are 3-8 times for the near-source stations, and 1-3 times for the stations on the east-southeastern side of IWTH26. Site amplification factors at the HND0FF station located above the top edge of mainshock fault plane have different characteristics; 3 times at 0.5 Hz, about 1 time at 1-7 Hz, and a spectral sag at 3 Hz. For the propagation path effect in the fore-arc region within 100 km of the source region, Q_S is estimated to be 40ƒ ^1.0 in a frequency range of 0.5-7 Hz.

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A great geo-disaster occurred in the 2008 Iwate-Miyagi Nairiku Earthquake. Therefore, evaluation with high accuracy of the strong seismic motion at the damaged sites is very important to analyze the failure mechanism. However, there are no strong motion observation stations near the watercourse closure sites during this earthquake. In this study, the seismic waveforms at Ichinonohara, Nuruyu and Sakashita, where watercourse closure took place, were estimated based on empirical site amplification and phase effects. The estimated seismic motions will be useful for rational safety assessment of natural slopes.

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The 2008 Iwate-Miyagi-Nairiku Earthquake, which hit Iwate, Miyagi and Akita Prefectures in Japan with a JMA magnitude of 7.2 on June 14, 2008, caused various kinds of geotechnical damages in the epicentral area. This paper describes the relations between the permanent displacements of ground and damages of soils mainly including slope failure caused by the earthquake. The permanent displacements of ground were obtained using both the position data of the GEONET system operated with aid of GPS and the displacement records numerically estimated from strong ground motions. It is concluded that the permanent displacement of ground can explain well the geotechnical damages occurred during the earthquake rather than strong motion data such as acceleration amplitude and seismic intensity scale.

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A huge landslide was generated in the Aratosawa dam at an upstream site during the 2008 earthquake, which hit volcanic mountain area of northern inland Japan. It was about 1.3 km in length, about 900 m in width, and the amount of movement mass totaled approximately 67 million m³ slipped about 320 m. In this paper, the soil properties of the sliding portion are reported, and the time series of the slide and the cause of the slide are discussed by the strong motion data at the dam site and the results of sliding block analysis. It was found that the effective stress reduction during the earthquake is the key issue of the earthquake induced land slide.

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The 2008 Iwate-Miyagi Nairiku earthquake caused more than 50 landslide dams made of the collapsed soils and rocks. In this paper the geotechnical properties of a landslide dam were investigated in order to study the stability of landslide dam against seepage and overtopping. The in-situ tests were carried out at Yunokura landslide dam which is one of the largest landslide dams along the Hasama River. In addition the laboratory tests with the disturbed samples obtained at Yunokura were performed. The tests results show that the rock ratio in the boring core varied with depth. The soil parts without rocks were relatively soft with lower N values and lower elastic wave velocities. The permeability coefficients of plastic soil samples were lower than the coefficient measured at the bore hole. The erosion resistances of the samples were higher than that of a non-plastic soil.

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The failures of the road infrastructures due to a slope failure during an earthquake such as the 2008 Iwate-Miyagi earthquake and 2008 China Wenchuan earthquake are issued. The induced slope failures cause the various failure modes of road structures. We classified the failure modes of a road structure due to the slope failure by analyzing the 196 database on the damage of road structures in the 2008 Iwate-Miyagi earthquake from the view point of the geological features and the distance from the hypocenter. In addition, based on the analysis for total 531 database on the damage of the road structures, the related damage functions by peak ground acceleration and peak ground velocity are developed.

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This paper discusses the difference of the damage level of the three schoolhouses in the vicinity of the epicenter of the 2008 Iwate-Miyagi Nairiku Earthquake with respect to ground response characteristics. We conducted microtremor measurements and aftershock observation at the site of Kaminome. One-dimensional equivalent linear analysis of the ground and three-dimensional seismic response analysis of the schoolhouse indicate that damage level of the schoolhouse of Kaminome meets good agreement with phenomenon considering non-linearity of the fill.

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