This paper describes main challenges and foresights of investigation and observation methods on landslide studies through overview of technological progress in those subjects.
There were much development and introduction of new technology, such as drilling techniques and survey method as LiDAR. However, there still remain inadequate situations in understanding of geological distribution and structure.
As to observation of landslide movement, measurement of the pore water pressure at slip surfaces are indirectly measured by water level in borehole for a long time until present, and it needs more desirable improvement to measure the actual pore water pressure.
Although various kinds of monitoring instruments have been improved and that the observation system has become automatic and convenient, comprehensive observation of the landslide movements on the field is not fully carried.
Active efforts are needed to develop solutions for these issues towards the future. Instrumentation for landslide monitoring is an indispensable technology for implementation of non-structural measures and performance based design of structural measures. Further development is desired towards the future.

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This paper conducted logistic regression analysis for landslides induced by earthquake within pre-existing landslide topographies. The logistic regression model constructed by using the landslides data set from the Chuetsu earthquake. The results showed that surface roughness and marginal erosion ratio are the most influential factors for the landslide occurrence. The model was validated by the landslides data set of the Chuetsu earthquake and the Iwate-Miyagi inland earthquake. Based on ROC curves, the AUC is larger than 0. 8, showed good prediction accuracy and suggested the method is useful.

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A new approach named polyhedron method is proposed for estimating underground sliding plane geometry by analyzing only ground displacement vectors. The displacement vectors are calculated from three-dimensional positional data of ground points surveyed in the landslide area at different times, and a three-dimensional underground sliding plane geometry is estimated by the polyhedron which consists of triangular surfaces. The proposed method is applied to actual landslide areas of Shin-yasu landslide and Aidoji landslide in Nagano prefecture.

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At the crown of Aratozawa landslide triggered by the Iwate-Miyagi Nairiku Earthquake in 2008, a downhill-facing scarp developed rapidly after main shock. About the same time, uphill-facing scarps and lateral bulge of lower slopes were developed in a lower layer of cap rock composed of pumiceous tuff. As a shear strain concentrates in pumiceous tuff and generates plasticity displacement, high-angle shears occurred in pumiceous tuff. Those shears have a possibility of Riedel shears R2 made by layer parallel simple shear by cyclic horizontal vibrations. These shears decreased strength of pumiceous tuff and sliding of Aratozawa landslide decreased minimum principal stress of rock masses. Gravitational creep was caused by these factors.

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