Terrain correction algorithms for urban microgravity surveys: Applications in revealing buried faults in urban noise working conditions

Abstract The dense clusters of buildings in cities considerably affect the accuracy of urban microgravity measurements. This study introduced a set of new high-precision algorithms for calculating vicinity, median- and far-zone terrain correction to solve precision problems of gravity surveys on the magnitude of the microgravity scale in cities. The vicinity and median-zone algorithms first divided complex artificial buildings and natural terrain into a set of multiple triangles and then calculated corresponding analytical solutions for each triangle. Finally, we obtained high-accuracy terrain correction values by accumulating; errors only occurred from the fitting degree between triangulation and real terrain features, but the subdivision of the triangular mesh was finer, and the calculation precision was higher. Far-zone algorithms use open global high-resolution digital elevation model (DEM) data to calculate gravity terrain corrections, and the DEM grid nodes used here were up to 30 m. To increase the effective detection accuracy of urban microgravity explorations using these new methods and to further compare their practical application in urban geological surveys, the exploration effects of microgravity, micro-tremor, transient electromagnetic, and reflection seismic methods were compared and analyzed using the buried Sumatou fault in the main urban area of Tianfu new district in Chengdu as an example, The results revealed that the microgravity method has good adaptability to field conditions and is not affected by urban noise such as power line electromagnetic and traffic vibration fields. Therefore, areal microgravity measurements can be used to investigate buried urban faults.