Inferring geologic structure from gravity anomalies: Proceed with caution

Characterization of key geologic structures within a study region, such as basin depths, fault offsets, and fault dip, are often derived from gravity data. Gravity modeling of such subsurface geologic structure generally assumes either homogeneous or spatially uncorrelated densities within modeled rock bodies and overlying sediments. This assumption allows modeling to focus on the shape of the subsurface bodies, for example, body depth or fault dip, which then underpin subsequent structural interpretations. However, both surface and drill-hole samples from rock bodies and sediments show a range of density values that exhibit spatial correlation, The spatially-correlated densities add low-frequency noise to the models that is difficult to detect and characterize  which can lead to misinterpretations of the subsurface structure.