Many landslides occurred in a large area during the 2008 Iwate-Miyagi Nairiku Earthquake. The greatest landslide and disaster on record occurred in Aratozawa near the seismic fault. Therefore, evaluation by high accuracy of the strong seismic motion at the Aratozawa landslide is very important to analyze the landslide mechanism. Hence, the evaluation of seismic response characteristics at this site is necessary. In this study, seismic waveform at the Aratozawa landslide was estimated based on empirical site amplification and phase effects. Site amplification characteristics at the Aratozawa landslide were evaluated based on the aftershock observation records. Moreover, a characterized source model for strong ground motion prediction was constructed based on the results of waveform inversion for this earthquake.

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In this study, we investigated the influence of temperature on the residual strength of soils. Results of ring shear tests performed on thirteen soil samples at temperatures ranging from about 5°C to room temperature revealed that shear strength of specimen which contain high fraction of smectite (swelling clay mineral) decreased when temperature was low. Ca-type bentonite was subjected to cooling and heating tests, then stick-slip behaviors were characteristically observed under high temperature condition, implying that shear behavior changes in response to temperature condition. In addition, shear weakening of Ca-type bentonite under low temperature condition was observed under shear rates lower than 0. 1mm/min. Stress-controlled experiment was also performed on smectite-rich Tertiary clay, and then creep-like displacement occurred due to shear weakening by cooling. These results imply that if slip surface soils contain abundant smectite, decrease of underground temperature can lead to lowering of shear resistance of slip surface, triggering landslide movement. In order to elucidate the mechanism of landslide behaviors whose triggering mechanism is still unknown, some attention should be also paid to fluctuation patterns of underground temperature.

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The article of Journal of the Japan Landslide Society, "Residual shear behavior of serpentinite in Shiraishi landslide, Tokushima Prefecture and sliding mechanism" by G. Wang et al., published in Volume 47, Issue 5, pp.265-273, has been retracted by the agreement between the authors and the journal's editorial committee. The retraction has been decided, since most of figures and findings of this article are duplicated with another article published in advance by G. Wang et al., Earth Surface Processes and Landforms, Vol.35, pp.407-416, John Wiley & Sons, Ltd., 2010, and therefore, in violation of journal's policies regarding the prevention of duplicate publication.

 

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The editor-in-chief of Journal of the Japan Landslide Society (September 1, 2017)

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In this study, we have reinvestigated the spatial distribution of shallow landslides in Izumozaki area, Niigata, caused by the heavy-rainfall in August 1961 and July 2004, by analyses using high resolution ortho images and a 2-m DEM. The results are as follows. The landslides occurred in 1961 are more than twice that in 2004. Among the 2004 landslides, the ratio of the landslides along roads is very high (1961: 4. 2%; 2004: 16. 4%) . More than half of landslides in 2004 (about 70 percent as the number ratio, 54 percent as the area ratio) were primary landslides in a valley side slope not including the 1961 landslides. Primary landslides occurred randomly on outfacing slopes and infacing slopes, if lithological and topographic conditions were the same. Most of the1961 landslides expanded due to the 2004 rainstorm developed on the upper part of slopes. These enlarged landslides tend to occur on slopes with daylighting beds except for the Nishiyama Formations.

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