Gravity surveying involves looking at the subsurface structure based on the differences in densities of the subsurface rocks. The idea is based around a causative body - one which produces a gravity anomaly. Assessment of gravity anomalies can give ideas about depth, size and shape of the causing body. Gravity anomalies are measured in ms-2. As the anomalies are very small compared to the Earth's field (9.81ms-2), they are commonly expressed in gravity units (g.u.), where 1 gu = 1μms-2.
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GeologyRocks