Near-surface Velocity Characterization through 3D Joint Inversion of Seismic Travel-Times and Gravity Data

D. Colombo¹, D. Rovetta¹, and E. Sandoval Curiel¹

Abstract

The near-surface velocity distribution in the Arabian Peninsula is complicated by geomorphological features typical of desert environments such as dunes, wadis and sabkhas and by the presence of karsts in shallow limestone and evaporitic rocks. This complex model is difficult to characterize with seismic travel-time tomography, due to the shallow velocity inversions and to the poor quality of the first arrival travel-time picks. Moreover, since the kinematics of the refracted waves makes them more sensitive to high velocity features, localized low velocity anomalies are undersampled and cannot be properly reconstructed. Gravity measurements are sensitive to density variations in the shallow subsurface and density correlates consistently with P-wave velocity in most rocks. A joint inversion of seismic travel-times and gravity data is therefore a more robust approach for solving the difficult problem of such a complex near-surface characterization. A novel 3D simultaneous joint inversion scheme for gravity and seismic travel-time data was developed, including various model regularization functions such as a-priori parameter distribution information, solution-space bounds, structural similarity constraints and rock physics relations. An efficient and robust joint inversion workflow is demonstrated against a synthetic model representing a complex pattern of near-surface anomalies incorporating low-velocity (or high-velocity) and low-density (or high-density) bodies. Results demonstrate that shallow anomalies are better reconstructed by the joint inversion rather than that obtained by the single-domain inversions. Finally, the algorithm is tested with real data from Saudi Arabia acquired over a wadi structure, showing that the joint inversion algorithm can significantly improve the seismic imaging. The developed methodology is part of a multi-geophysics platform for near-surface velocity model building in complex geology scenarios.

AAPG Search and Discovery Article #90188 ©GEO-2014, 11th Middle East Geosciences Conference and Exhibition, 10-12 March 2014, Manama, Bahrain