Seismic refraction investigation on near surface landslides at the Kundasang area in Sabah, Malaysia

摘要

Surface geophysical method was used in studying the effect of natural disaster impact and subsurface physicalchanges located in an active geohazard zone at the Kundasang area in Sabah, Malaysia. The natural disaster impactwas a previous surface and subsurface ground damage caused by a landslides activity, and the consequent civilengineering infrastructure failure. 2D seismic refraction tomography (2DSRT) was used in evaluating the continuoussubsurface ground damage with particular reference to geomaterials and landslide features based on compressionalwave (Primary velocity, vp) results. A total of four spread lines were conducted in two different zones (Northeast and Southwest zone) in Kundasang Secondary School (SMK Kundasang). Primary velocity data was acquired andrecorded using ABEM Terraloc MK6 seismograph with the seismic wave being triggered by an impact and detectedby arrays of sensitive devices called geophones. 2D seismic refraction primary velocity results representingsubsurface profile for each survey line were calculated to determine time and depth of the subsurface profileinvestigated based on linear and delay time analysis supplied by Optim software package and supported by previousborehole data. The seismic refraction method identified three main layers of geomaterials which contained asubsurface landslides anomaly within the layers. The results consist of top soil/residual soil (330 600 m/s) 0 6 m,weathered zone with a mixture of soil, boulder and rock fractured (500 1900 m/s) 2 25 m and fresh rock/bedrock(> 2300 m/s) from 8 m depth. The landslides geometry was determined inconsistently within the survey line from 3 25 m (thickness), 57 and 75 m (width) and 100 m and more (length) with a primary velocity of 700 1800 m/s. Theseismic refraction profiles obtained also revealed that the landslide occurrence extends from the southeast zone andcontinuously heading towards the northeast zone. A good matching seismic refraction results was obtained andcalibrated using borehole results which shows that this technique was appropriate to be applied in near-surfacelandslide assessment which can further substantiates and compliments borehole data and others physical mapping