| Popis: |
Deep subsurface weathering has traditionally been measured by quantifying variations in weathered material properties through cores and boreholes. However, cores collected from the subsurface necessarily sample a minimal fraction of the subsurface. On the other hand, geophysical surveys can be used to obtain a representative perspective of the subsurface. To better understand the near-surface weathered layers, the paper presents an application of rock physics modelling with the help of field-based seismic refraction measurement. We acquired seismic refraction data in hillslope using 4.5 Hz natural frequency geophone with 5-meter geophone spacing. We estimated the subsurface compressional (P) wave velocity (VP) structure and mapped the seismic profile. The profile demonstrated saprolite thickness varying from 1 to 2 meters. To better identify the weathered layers (saprolite) in this section, we predicted porosity using the velocity-porosity relationship model. The porosity estimated through the model was validated by the porosity of the sample extracted from boreholes. This study shows how low-cost techniques can provide useful information about near-surface complexity. Therefore, from this study, it was concluded that proper identification of near-surface layers requires a combination of complementary field-based measurement and precise lab-based rock physics measurement. |
