Characteristics of Subsurface Materials: Integration of Seismic Refraction, 2-D Resistivity Imaging and Geotechnical Borehole Logs
Senior Lecturer (Dr.)
Nur Azwin Ismail
Social Science Officer
Geophysical investigations are best utilized to study subsurface characterization. Geophysical methods used during this investigation included the seismic refraction and 2-D resistivity imaging methods were conducted along north-south direction of 8 km in Lenggong, Perak, Malaysia with integration in geotechnical borehole logs. The purpose of the geophysical survey was to map bedrock, structure and fracture of the shallow subsurface. Seismic data at this site was affected by steep topographic terrain prohibited the placement of far-offend shots and limiting depth of penetration. 2-D resistivity imaging data are inherently more smoothed than seismic refraction data. Borehole data alone is not adequate measure of subsurface condition in huge study area. Therefore, an integrated approach combining all three methods was a successful (cost-effective) means of characterizing subsurface as opposed to any singular method. Geophysical data indicate that the top litho-layer is thinner towards south and north. Alternating alluvium consisting of boulders (weathered granite) and granitic bedrock sequences were observed in the refined resistivity results. Based on 2-D resistivity imaging results, fractures and faults were identified within the granitic bedrock and other potential areas of poor rock quality. Preliminary borehole logs information was used to refine both seismic and resistivity results. Seismic refraction survey provided different and complimentary results. While not capable of differentiating between the different rock units, the seismic refraction provides more accurate subsurface thickness and bedrock velocity. Therefore, integration of seismic refraction, 2-D resistivity imaging and borehole logs methods match and can be used for shallow subsurface works.
Keywords: Subsurface, lenggong, fracture, seismic refraction, 2-D resistivity imaging, borehole.
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