Many landslides occurred in a large area during the 2004 Mid Niigata Prefecture Earthquake. The greatest landslide and disaster occurred in Higashitakezawa, old Yamakoshi village near the seismic fault. Therefore, to clarify the landslide mechanism, it is necessary to estimate strong ground motions at Higashitakezawa landslide with sufficient accuracy, taking into account site effects. In this study, seismic waveform at the Higashitakezawa landslide was estimated based on empirical site amplification and phase effects. Site effects at the Higashitakezawa landslide were evaluated based on seismic observation records at the New Kogomo Community Center. Difference of site effects between the Higashitakezawa landslide and the Yamakoshi Branch of Nagaoka City was indicated.

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Monitoring of ground surface deformation is important for determining and implementing effective measures against landslide disasters. Synthetic aperture radar interferometry (InSAR) is a promising monitoring technique that can detect surface deformation in wide areas at the centimeter scale. The present study aimed to interpret landslide deformation using InSAR images that cover the Shimekake landslide area in Yamagata Prefecture, Japan. The study area consists of gentle slopes (approx. 10°) facing southwest direction and predominantly lies on Neogene mudstone. Landslides in the area were triggered by snowmelt. InSAR images were produced from Advanced Land Observing Satellite (ALOS) /Phased Array L-band SAR (PALSAR) data that were measured from ascending/descending orbit (viewed above from west/east) . For detecting landslide deformations, we selected the data measured between June 2006 and October 2008 because it displayed the best coherence among the available archived PALSAR data. Previous 2.5-dimensional analysis revealed east-west and vertical displacement using InSAR images obtained from both ascending (northward) and descending (southward) orbits. We compared the displacement estimated by InSAR with that measured by GPS between December 2009 and March 2010. The comparison revealed that westward displacement in the entire landslide area and subsidence at the landslide scar identified by InSAR was coincident with that of the GPS measurements. Although no GPS data were available between June 2006 and October 2008, it is thought that the same landslide deformation has continued since June 2006. Therefore, we concluded that the InSAR images successfully detected landslide deformation in the study area. Notably, however, uplifting displacement detected at the foot of the landslide was not coincident with that of the GPS measurements, and the discrepancy was possibly due to a partial phase-unwrapping error in the InSAR image obtained from the ascending orbit. Despite the detection of false displacement, it was found that InSAR can serve as an effective reconnaissance tool for the monitoring of subtle landslide deformations over wide areas and is expected to support the location planning of GPS survey equipment in the field for effective landslide deformation measurements.

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