Knowledge on the near-surface is used for civil engineering purposes. Features may be natural or man-made.
Quad Geometrics

Gravity can identify sinkholes and caves as geohazards, and can likewise detect karst terrain also for engineering applications. Castello et al. (2010) used microgravity to investigate subsurface cavity in urban Naples, Italy. Kobe et al. (2019) monitored leaching and transfer of soluble and dissolved rocks in the subsurface of Bad Frankenhausen, Germany by time-lapse microgravity. Tuckwell et al. (2008) discussed the use of microgravity to detect small voids and low-density ground for engineering purposes.

Mouyen et al., (2020) quantified sediment mass redistribution in a wide meander of a river and a slow landslide in Taiwan from joint time-lapse gravimetry and photogrammetry surveys. They surveyed 10 stations with CG-5 (relative) and A-10 (absolute) gravimeters in november of 2015, 2016 and 2017. At the same times they generated high-resolution digital surface models from a drone to quantify the sediment volume. They could estimate a slow landslide causing a sediment mass loss of 3.7 +/- 0.4 x 109 kg over 2 years.

modeled depth to bedrock. bottom: cross-section showing the depth to bedrock and densities. top: observedgravity in blue and residual after modeled gravity is subtracted in red. from tassis et al., (2014).

Variations in the depth to bedrock can be estimated from gravity when there is a significant density contrast with the overlying, usually unconsolidated sediments. In parts of the world with strong density contrasts such as Scandinavian post-glacial marine sediments this can be a cost-effective way of mapping prior to building of roads, develop urban areas, etc.