JOINT INVERSION OF SEISMIC TRAVELTIMES AND GRAVITY DATA ON THE MICANG FORELAND FOLD BELT AND ITS HYDROCARBON POTENTIAL

The Micang foreland fold belt is a transitional zone between the Qinling orogen and Sichuan Basin. Affected by multi-stage tectonic processes and complicated driving forces, the Micang foreland fold belt can not be successfully traced in the seismic sections, due to its complex geological structures. We present a detailed 2D density and velocity transects for the upper crust across the Micang foreland belt using a joint seismic reflection and gravity inversion technique. We use a weighted least square scheme to simultaneously invert the density and velocity. This technique parameterizes the crust as a set of layers that are based on published geologic and seismic models. Each layer has a uniform density and velocity that are constrained where possible by borehole measurements, seismic velocities, and petrologic data. Then the joint inversion of travel time and gravity data is performed to find out a common model having an optimum fit of both travel time and gravity data. Since the global misfit is the addition of the contribution of the two methods, we add a weighting factor in the objective function to better coordinate these two different kinds of data. After being tested with a multi-layered model, the joint inversion scheme is adopted for the Micang foreland belt to construct a more complete upper crustal image. We finally discuss the presence of the overthrusted structure in terms of interaction between the Qinling orogen and Sichuan Basin.