Gravity Theory Measurement practices –Relative –Closed loops Corrections –Drift –Free Air –Bouguer –Terrain Interpretation –Modeling.

Gravity

• Theory• Measurement practices

– Relative– Closed loops

• Corrections– Drift– Free Air– Bouguer– Terrain

• Interpretation– Modeling

Worden Gravimeter

Inside the Worden

Closing the Loop

Elevation Corrections

Free Air Correction

Bouguer Correction

Gravity Corrections

• Drift Correction(tobs-tbase) x drift rate

• Free Air Correction(hobs-hbase) * 0.3086 mgal/m

• Bouguer Correction(hobs-hbase) * 0.04193 mgal/m

where = density in gr/cc

Gravity Anomalies

• Free Air Anomaly gfa = (gobs-gbase) – (drift corr) + (fa corr)

• Bouguer Anomaly

gb = gfa –(bouguer correction)

Gravity Corrections(sample)