3-D VELOCITY STRUCTURE FROM SIMULTANEOUS TRAVEL-TIME INVERSION OF IN-LINE SEISMIC DATA ALONG INTERSECTING PROFILES

A method for simultaneously inverting in-line seismic-traveltime data recorded along a network of intersecting linear profiles is presented. Consistency of the models at the intersection points is assured and permits 3-D structural and velocity variations to be inferred by interpolation between the profiles. Common model parameters are used at the intersection points, thereby minimizing the number of independent model parameters and maximizing the degree of constraint of each 2-D model. The method has two main applications: (1) to obtain the most constrained set of 2-D models for each profile if subsequent 3-D modelling is not possible, and (2) to provide a 3-D starting model for subsequent 3-D modelling if there is sufficient azimuthal data coverage. Some ideal line geometries are suggested, but the method is applicable to any set of two or more lines with one or more intersection point. A new interpretation of crustal seismic data from the Peace River Arch region of the Western Canada Sedimentary Basin, consisting of four profiles, is presented using the simultaneous-inversion method for both refracted and reflected arrivals. The results are generally consistent with a previous interpretation of the data in which each profile was modelled independently of the others using 2-D forward modelling. However, the models obtained by inversion contain less lateral heterogeneity that more accurately reflects the resolution limits of the data. This illustrates the need to reconsider data that have only been analysed by forward modelling.