Detection of Cover Collapse Doline and Other Epikarst Features by Multiple Geophysical Techniques, Case Study of Tarimba Cave, Brazil

Reliable characterization of the karst system is essential for risk assessment where many
associated hazards (e.g., cover-collapse dolines and groundwater pollution) can a ect natural and
built environments, threatening public safety. The use of multiple geophysical approaches may o er
an improved way to investigate such cover-collapse sinkholes and aid in geohazard risk assessments.
In this paper, covered karst, which has two types of shallow caves (vadose and fluvial) located
in Tarimba (Goias, Brazil), was investigated using various geophysical methods to evaluate their
e ciency in the delineation of the geometry of sediments filled sinkhole. The methods used for
the investigation were Electrical Resistivity Tomography (ERT), Seismic Refraction Survey (SRS),
Seismic Refraction Tomography (SRT) and the Very Low Frequency Electromagnetic (VLF-EM)
method. The study developed several (2D) sections of the measured physical properties, including
P-wave velocity and electrical resistivity, as well as the induced current (because of local bodies).
For the analysis and processing of the data obtained from these methods, the following approaches
were adopted: ERT inversion using a least-square scheme, Karous-Hjelt filter for VLF-EM data
and time-distance curves and Vp cross-sections for the SRS. The refraction data analysis showed
three-layered stratigraphy topsoil, claystone and carbonate bedrock, respectively. The findings
obtained from ERT (three-layered stratigraphy and sediment-filled doline), as well as VLF-EM
(fractured or filled caves as a positive anomaly), were found to be consistent with the actual field
conditions. However, the SRS and SRT methods did not show the collapsed material and reached
the limited the depth because of shorter profile lengths. The study provides a reasonable basis for
the development of an integrated geophysical approach for site characterization of karst systems,
particularly the perched tank and collapse doline.