Applying the Seismic Refraction Tomography for Site Characterization

AbstractSeismic refraction method is a geophysical method that has been developed for shallow subsurface investigation. It provides 2-dimensional profiles including depth and distance that simplified the characterization of relatively large volumes of the subsurface. Interpretation of seismic refraction data using seismic tomography involves continuous velocity gradient across a subsurface which is more effective for site characterization compared to conventional seismic refraction. Three parallel seismic refraction survey lines were conducted at Kaki Bukit, Perlis with the aim of characterizing the subsurface of the area. 2m geophone spacing was used with total length of 46m. The separation between lines is 20m. Weight drop of 20kg and steel plate were used as seismic source. A total of 20 shotpoints were performed for survey line L1, 23 shotpoints for survey line L2 and 22 shotpoints for survey line L3. The high quality seismic data obtained were then processed using SeisOptPicker and SeisOpt2D software to produce a seismic tomography section for each survey line. Results indicate that the study area is said to have 4 main layers with velocity increase fairly with depth. The first layer with velocity 300-500 m/s predominantly consists of top soil and form overburden. Second layer with velocity 500-800 m/s is suggested to be a highly weathered limestone. The third layer represents by highly fractured limestone with velocity 800-1500m/s. Limestone bedrock represent by the fourth layer with velocity > 2000m/s. Competent limestone bedrock is identified at survey line L3 with velocity > 3000m/s

Slope Failures Evaluation and Landslides Investigation Using 2-D Resistivity Method

Slope failure is a complex phenomenon that may caused to landslides. Buildings and infrastructure such as transportation facilities and pipelines located within the boundaries of a landslide can be damaged or destroyed. Slope failure classification and various factors contributing to the instability using 2-D resistivity survey conducted in Selangor, Malaysia are described. Six 2-D resistivity survey lines with 5 m minimum electrode spacing using Pole-dipole array were performed. The data were processed using Res2Dinv and surfer10 software to evaluate the subsurface characteristics. The 2-D resistivity results show that the subsurface consist of two main zones. The first zone was alluvium or highly weathered with resistivity value of 100-1000 Ωm and depth of >30 m. This zone consists of saturated area with resistivity value of 1-100 Ωm and boulders with resistivity value of 1200-7000 Ωm. The second zone with resistivity value of >7000 Ωm was interpreted as granitic bedrock. The study area was characterized by saturated zones, highly weathered zone, highly contain of sand and boulders that will trigger slope failure in the survey area. On the basis of the case examples described, 2-D resistivity method is categorized into desirable and useful method in determination of slope failure and future assessments

Enhancement in resistivity resolution based on the data sets amalgamation technique at Bukit Bunuh, Perak, Malaysia

In this paper, we have carried out a study with the main objective to enhance the resolution of the electrical resistivity inversion model by introducing the data sets amalgamation technique to be used in the data processing stage. Based on the model resistivity with topography results, the data sets amalgamation technique for pole-dipole and wenner-schlumberger arrays are successful in identifying the boundary or interface of the overburden and weathered granite. Although the electrical resistivity method is well known, the proper selection of an array and appropriate inversion parameters setting such as damping factors are important in order to achieve the study objective and to image the target at the Earth’s subsurface characterizations