Gravity

Applications

• Geological mapping
• Karstic and void detection
• Mineral exploration
• Depth of sediments
• Archaeology

Method

Microgravity is a potential field geophysical technique used to record accurately localised variations in the earth’s gravitational field. The variations in gravitational readings are caused by density contrasts of the rocks and sediments beneath the reading location. Thus measurements of gravity are an indicator of the different subsurface rock densities and through careful interpretation, an accurate image of the subsurface can be inferred. For near-surface investigations, local variations in the gravity field are influenced by factors such as the bedrock depth, overall density of the subsurface material as well as fracturing and voids typical in karst environments.

Gravity surveys are acquired using highly sensitive instruments that have the capability of measuring very minute variations in the earth’s gravitational field. In a typical survey the gravity acquisition system is positioned at specific locations at equal distances, levelled and then allowed to run automatically until a stable gravity reading is achieved. The system is then moved to the next successive locations to acquire further readings. Generally, the deeper the target anomaly the larger the diameter would need to be to produce a recordable gravity anomaly.

Data Analysis & Presentation

After correction of gravity datasets for elevation, earth tidal effects, topography, latitude and instrument drift a plan view image showing variations in the Bouguer Gravity measured in milliGals can be produced. Note depth information to targets generally cannot be obtained using microgravity.

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