IDENTIFATION OF LANSLIDE DIMENSION BASED ON SEISMIC REFRACTION SURVEY IN TENGKILK VILLAGE, KARANGANYAR, CENTRAL JAVA

Abstract

A seismic refraction survey was conducted at a landslide site, which had destroyed a road and several houses in Tengklik Village, Karanganyar, Central Java, Indonesia. The survey provided insight into the slope stratigraphy, as well as the dimensions of sliding area and depths of the slope failure planes. Field observations and drill-hole data were used to verify the accuracy of seismic refraction data. The seismic velocity measured in the top - sliding layer of sandy silt was less than 900 m/sec, while that in the underlying layer of silty sandstone ranged from 2400 to 900 m/sec. The stable bedrock of andesite breccia underneath the sliding soil layers was about 2500 m/sec. It was apparent that the failure surface was irregular, varies in depth. This failure plane exists at the contact of the andesitic breccia (bedrock) and the sliding layer of silty sandstone. The thickness of the sandy silt ranged from 3 to 5 m at lower part of sliding mass, while at the upper part ranged from 4 to 8 m. The estimated depth of the failure surface ranged from 12 to 24 m. The volume of mass movement is estimated about 111.386 m³ . It was also found that the presence of mountain block at the bedrock of andesitic breccia may resist the movement.