GATE-2018 (24) :Wyllie – Time average equation

GATE-2016

32. The value of free-air correction( assuming sea level as datum plane) at an elevation of 150m is......mGal

Solution:

Free air correction in Gravity : The free-air correction accounts for gravity variations caused by elevation differences in the observation locations.

The form of the free-air gravity anomaly (Δg_F), is given by

Δg_F = g_obs – g_n + 0.3086h mGal

g_{obs –} observed gravity anomaly

g_n – normal (or) therotical gravity anomaly

h – height (m)

Where h is the elevation (m) at which the gravity station is above the datum (typically sea level)

Free air correctio is = 0.3086 mGal /m

1m (free air correction) = 0.3068 mGal

150 m (free air correction) = ?

cross multiplication

x * 1 = 0.3086 * 150

x= 46.26 mGal

Therefore, free air correction for 150 m = 46.29 mGal