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 physical changes located in an active geohazard zone at the Kundasang area in Sabah, Malaysia. The natural disaster impact was a previous surface and subsurface ground damage caused by a landslides activity, and the consequent civil engineering infrastructure failure. 2D seismic refraction tomography (2DSRT) was used in evaluating the continuous subsurface ground damage with particular reference to geomaterials and landslide features based on compressional wave (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 and recorded using ABEM Terraloc MK6 seismograph with the seismic wave being triggered by an impact and detected by arrays of sensitive devices called geophones. 2D seismic refraction primary velocity results representing subsurface profile for each survey line were calculated to determine time and depth of the subsurface profile investigated based on linear and delay time analysis supplied by Optim software package and supported by previous borehole data. The seismic refraction method identified three main layers of geomaterials which contained a subsurface 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. The seismic refraction profiles obtained also revealed that the landslide occurrence extends from the southeast zone and continuously heading towards the northeast zone. A good matching seismic refraction results was obtained and calibrated using borehole results which shows that this technique was appropriate to be applied in near-surface landslide assessment which can further substantiates and compliments borehole data and others physical mapping data rapidly in a lower cost. Furthermore, this geophysical method adopts a surface technique that can minimise the disruption and damage to the site thus preserving a sustainable environment during the site investigation data acquisition stages.