Gravity measurements and terrain corrections using a digital terrain model in the NW Himalaya
Areas recently gravity surveyed in the NW Himalaya are characterized by high-elevation and high-amplitude topographic undulations. A new method of applying combined Bouguer and terrain corrections using a digital terrain model is highly accurate and offers advantages over conventional techniques by saving efforts and being more flexible. Partitioning parameters for station-dependent inner-zone compartments and station-independent outer zones can be optimally selected for the desired accuracy requirements. A digital terrain database is used to obtain the outer-zone corrections. In the situation of the NW Himalaya surveys, a 1.2km inner zone is divided into 112 compartments for each station and a digital terrain database containing nearly 16?000 data points for 30?30? compartments was applied using the computer program EFFECT.FOR, to compute combined Bouguer and terrain corrections for a 20km range. The terrain corrections between 20 and 170km were computed using National Geophysical Data Centre (NGDC) 5?5? gridded global elevation database. The magnitude of the terrain correction varies between 3 and 50mGal. The effects of the 20km range terrain correction are more pronounced on short-medium wavelength anomalies. The Swarghat gravity high is further enhanced while several high-frequency pseudo-anomalies disappear after applying the terrain corrections. The refined Bouguer anomaly varies from ?160mGal at the southern end of the section, to ?310mGal at the northern end, suggesting a Moho depth variation from 45 to nearly 60km. The steepness of the northward negative gravity gradient, typical for the Himalaya, is considerably reduced after applying a terrain correction for the 170km range.
gravity terrain correction himalaya bouguer anomaly digital elevation model