The use of geophysical characterization of karst systems can provide an economical and non-invasive alternative for extracting information about cavities, sinkholes, pathways for water infiltration as well as the degree of karstification of underlying carbonate rocks. In the present study, three geophysical techniques, namely, Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT) and Very Low Frequency Electromagnetic (VLFEM) were applied at three different and appropriate locations in fluvial karst of a listed environmentally sensitive area of the Rio Vermelho, Mambaí, Goiás, Brazil. In the data acquisition phase, the GPR, direct-current (DC) resistivity and VLFEM profiles were obtained at three different locations in the area. Data were analyzed using commonly adopted processing workflows. Different radar typologies have been assigned to soil and rock typse. The GPR results showed a well-defined lithology of the site based on the amplitude of the signal. On the other hand, the inverted resistivity cross-sections showed a three-layered stratigraphy, pathways of water infiltration and the weathered structures in carbonate (Bambui group). The interpretation of VLFEM as contours of current density resulted from Fraser and Karous-Hjelt filters, indicate the presence of conductive structures (high apparent current density) that may be linked with the weathered carbonate and other conductive and resistive anomalies may be associated with the water-filled and dry cavities (cave). The results encourage the integrated application of geophysical techniques as the reconnaissance for further detailed characterization of the karst areas.

A portion of the west of Mexico City is a densely populated area located in an abrupt topography, whose volcano-sedimentary materials increase the likelihood of landslides. This study uses Seismic Refraction Tomography (SRT) and Ambient Noise Tomography (ANT) methods to estimate the extent of landslide-prone materials at a test site. We exploited the geometry of a quadrangular array of surface sources and receivers to generate a Vp tomography image of the bedrock and surface-wave group-velocity tomographies of SRTand ANT in the frequency range of 6 to 26 Hz. We found that the best velocities correlation between the two methods is an average frequency of 24 Hz. The results show the areas of low velocity associated with materials that have lost their resistance due to the increase in pore pressure (Vs < 100 m/s) and the areas where eventually more landslides will occur (120 < Vs < 200 m/s) if mitigation work is not carried out. The most stable zones correspond to materials with velocity values greater than 250 m/s that overlap a substratum at an average depth of 8 m. In the case of a high risk of landslide, when it is not advisable to perform active source experiments, ANT can provide good results to determine the extension of the sliding materials.