Abstract
2-D resistivity method is an indirect method to the shallow subsurface survey for maintaining the geo-environment. It is used to measure the apparent resistivity of subsurface. EHR technique was developed in order to get detail and deeper penetration for shallow subsurface study. In this study, 2-D resistivity with Enhancing Horizontal Resolution (EHR) technique is adopted to map and characterize the shallow subsurface (mineral exploration, geology, engineering and environment) using Pole-dipole array. The locations are Pagoh, Johor; Nusajaya, Johor and Puchong, Selangor (Malaysia). The study associated with mineral exploration is Pagoh, Johor while for Nusajaya, Johor is associated with geology and Puchong, Selangor is associated with engineering and environment. The 2-D resistivity and Induced polarization (IP) were employed at Pagoh, Johor to study and detect the subsurface variation of resistivity and chargeability of iron ore in the area. Result of the 2-D resistivity as well as the Induced Polarization (IP) shows that the area is underlain by a thick alluvium with resistivity value of 10 - 800 ohm-m iron which has chargeability rate of 0.1 - 3 msec. A sedimentary case study was executed at Nusajaya, Johor shows sandstone contains iron mineral (30 - 250 ohm-m) and weathered sandstone (500 -1000 ohm-m). Interpretation of 2-D resistivity data at Puchong, Selangor showed a low resistivity value (and this could be an influence factor the increasing water level because sandy silt is highly permeable in nature. The borehole, support the results of 2-D resistivity method relating a saturated zone in the survey area. There is a good correlation between the 2-D resistivity investigations and the results of borehole records. The stratigraphy and structure of the three case studies (mineral exploration, geology, engineering and environment) can be mapped effectively using 2-D resistivity with EHR technique.
Highlights
Geophysical study provides supported data in order to save cost and time
This paper aims to show how 2-D resistivity methods were successfully used for detection in shallow subsurface
The important part of this study is to show that Enhancing Horizontal Resolution (EHR) technique can improve the 2-D resistivity pseudo section and prove to get deeper penetration. 2-D resistivity survey is to determine the subsurface resistivity distribution by taking measurements on the ground surface
Summary
Geophysical study provides supported data in order to save cost and time. Geophysical methods can be used to determine depth of bedrock, nature of overburden materials and near surface structures such as sinkholes, cavities, voids, faults and boulders [1]. This paper aims to show how 2-D resistivity methods were successfully used for detection in shallow subsurface. An important part of this study is to improve the 2-D resistivity horizontal resolution and prove a detail image of deep structure can be obtained using EHR technique. 2-D resistivity method is used to determine the electrical resistivity structure of the subsurface (Figure 1). Resistivity is defined as a measure of the opposition to the flow of electric current in a material. The resistivity of a soil or rock is dependent on several factors that include amount of interconnected pore water, porosity, amount of total
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