Gravity is measured on top of a at continental plateau h 30

Gravity is measured on top of a at continental plateau h = 3:0 km above sea level. It is found that gravity is 750 mgal less than the value expected for the reference spheroid at the latitude of the plateau. The thickness of the normal crust (away from the plateau) is D = 35 km. The density of the crust is c = 2800 kg/m3, and the density of the mantle is m = 3300 kg/m3. a) Calculate the Free Air Correction and the Free Air Anomaly for the Plateau. b) Calculate the Bouguer Correction and the Bouguer Anomaly.

Solution

a. free air correction Cf= 3.086 h where h is elevation in m

= 3.086 x 3000 = 9258

for 0.1 gu accuracy station elevation is needed 4cm

for 750 mgal it will be 750 x 4=3000 cm or 30 m

free air anamoly = gobs+ Cf

b. bouguer correction Cb= 0.000419 x height difference x density = 0.000419 x 35000 x 2800 = 41062

bouger anamoly= delta gpbs+ Cf-Cb

= 750+ 9258-41062= -31054