Applications of seismic methods for cavity exploration

The presence of near surface cavities resulting from excavating effects of underground water is very common in carbonate rocks. These excavations can serve as accommodation spaces for fresh groundwater accumulation suitable for exploitation. However, in certain circumstances they can pose serious environmental and geotechnical problems in case they occur beneath residential and urban structures. Because of the widespread presence of carbonate rocks in Oman, surface and subsurface cavities can be found in many areas over the Sultanate. In fact, these cavities have even caused some major problems for residential areas; thus, detecting them and investigating their key properties can help in exploiting freshwater they may contain and mitigating the risk associated with them. Seismic refraction and surface wave methods have been widely used for near surface characterization. These methods have demonstrated several successful applications in detecting near surface cavities in many areas over the world. In this project we conduct seismic refraction tomography and multi-channel surface wave analysis (MASW) method to study seismic properties of cavities on surface and in subsurface. The first method provides P-wave velocity-depth model, while the second produces S-wave velocity-depth model of subsurface structures. Having P-wave and S-wave models will enable us to characterize the targeted geological formations and to derive a number of their qualitative elastic properties such as Poisson Ratio, stiffness, Young modulus. To support the interpretations from the seismic methods, gravity and GPR data also will be collected and analyzed. We will start by characterizing formations honoring cavities on the surface such as Bimmah sinkhole located in Qurayt, North Oman. This will allow us to calibrate our recorded data with observation and surface data. Conclusions and lessons learned from the characterized cavities will be implemented in searching for hidden cavities in the area. The study can provide key features that would allow future investigations in other areas in the Sultanate.