Characteristics of Movements of the Reactivated Shimekake Landslide since 25^th February 2009 in Tsuruoka City, Yamagata Prefecture, Northeastern Japan: Flash Report

Abstract

 On February 25, 2009, damage was reported for the first time from the Shimekake landslide located in Yamagata Prefecture. Landslide activity has increased since April. The active landslide extends up the opposite bank of the Kariya River, and is 400 meters wide and 700 meters long. The authors have conducted field surveys several times since the beginning of April, and have begun displacement monitoring of the landslide using GPS. As a result, the main block of the north side of the Kariya River showed a direction of movement from south-southwest to south and the sub-block at the south side of the Kariya River showed a southeasterly movement. The rate of horizontal displacement was large at the lower side of the slope. It tended to accelerate after rainfall, and reached 15 cm/day in the sub-block. The existence of two or more slip surfaces is presumed in the sub-block based on the properties of cracks at the block boundary and the characteristics of movements of the landslide.