Full text loading...
-
Characterization of a cave by means of microgravity and electrical resistivity 3D-inversions: Zé de Braga cave (Mira de Aire, Portugal)
- Source: First Break, Volume 36, Issue 10, Oct 2018, p. 29 - 34
-
- 01 Oct 2018
- Previous Article
- Table of Contents
- Next Article
Abstract
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.