Sub surface geometry of ar-rika and ruwah faults from gravity and magnetic surveys

Submitted to the Arabian Journal of Geosciences.10 GPS-Gravity profiles were conducted to provide sub-surface geometry of two sections of Najd Fault System (NFS) Ruwah and Ar Rika faults, six in the Afif and four in the Al Muwayh area about 500 km and 650 km west of Riyadh respectively. GPS surveys were collected in Differential GPS (DGPS) mode allowing a large area to be covered in limited time. DGPS is utilized for the advantages of accuracy, economy and speed. Output DGPS location coordinates were used in Free-air and Bouguer reductions, terrain corrections were applied using a 3 arc-second digital elevation model, finally isostatic and decompensative corrections were applied. Integration of the resulting decompensative isostatic residual anomalies and aeromagnetic map have mapped the NFS very accurately. Modeling the gravity field crossing the Ruwah fault zone revealed that it is associated with low gravity anomalies probably due to a complex of lower density crushed rocks, and modeled the geometry of the subsurface structure of Ar Rika fault as an inclined fault with reverse movement which would imply a compression component (post-dated the shearing) parallel to the plane of the cross-section