Gravity data as a tool for detecting faults: In-depth enhancement of subtle Almada's basement faults, Brazil.

We demonstrate the potential of gravity data to detect and to locate in-depth subtle normal faults in the basement relief of a sedimentary basin. This demonstration is accomplished by inverting the gravity data with the constraint that the estimated basement relief presents local abrupt faults and is smooth elsewhere. We inverted the gravity data from the onshore Almada Basin in northeastern Brazil, and we mapped several normal faults whose locations and plane geometries were already known from seismic imaging. The inversion method delineated well both the discontinuities with small or large slips and a sequence of step faults. Using synthetic data, we performed a systematic search of normal fault slips versus fault displacement depths to map the fault-detectable region in this space. This mapping helps to assess the ability of gravity inversion to detect normal faults. Mapping shows that normal faults with small (<0.5 km), medium (about 1 km), and large (about 2 km) vertical slips can be detected if the maximum midpoint depths of the fault planes are smaller than 1.8, 3.8, and 6.8 km, respectively. [ABSTRACT FROM AUTHOR]