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Characterization of a cave by means of microgravity and electrical resistivity 3D-inversions: Zé de Braga cave (Mira de Aire, Portugal)Normal access

Authors: F.J. Martínez-Moreno, F.J. Monteiro Santos, J. Galindo-Zaldívar, L. González-Castillo, A. Pedrera, I. Bernando, S. Gonçalves and J. Alves Ribeiro
Journal name: First Break
Issue: Vol 36, No 10, October 2018 pp. 29 - 34
DOI: 10.3997/1365-2397.2018004
Language: English
Info: Article, PDF ( 1.14Mb )
Price: € 30

Summary:
Using geophysical methods to locate unknown caves is a common practice. Here, we present a new code for cave modelling from the residual gravity anomaly. To test its effectiveness, the code has been applied to the well-known Zé de Braga cave, located in Mira de Aire-Santo Antonio Range within the Maciço Calcareo Estremeho (Portugal). This cave has a vertical entry (sinkhole) and develops in an L-form shape at 10-15 m depth within the Jurassic limestones of the massif. A 2D grid of resistivity and microgravity data were acquired over the cave. The cavity is highlighted by high resistivity values (~7500 ohm·m) and minimal values surrounded by maxima on the residual gravity map. The new gravity modelling code divides the sub-surface into blocks with densities of 0 g/cm3 (hole) to represent the cave, and 2.67 g/cm3 for the environment (limestones). The calculated 3D model of the cave is very close to the real morphology, dimensions and position, and is comparable to the inverted resistivities.


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