Abstract
The strain-rate tensor at a point on the surface of a landslide can be determined by setting up 5 stakes and measuring the rate of change of the distances between them . A suitable arrangement of stakes consists of 4 stakes at the corners of a square with 1 stake at the centre . Eight such patterns of stake arrange ment were used in the Ogawamura-Sodechi Landslide in 1987-1988 . Three independent components of the strain-rate tensor and their errors can be estimated by a least-squares method with 4 governing conditions derived from 8 distance measurements . The principal strain-rates are found to within about±6×10-4/day. The surface deformation pattern of the landslide, directions of the cracks and seasonnal variations of the landslide movement are well indicated by the strain-rate tensor and its invariants; namely, magnitude of the dilatation rate and maximum shear strain-rate. The previously reported model of the landslide movement is improved by the strain-rate tensor determianation.
