Flexible local seismic imaging in an integrated dynamic modelling framework

The proposed SIP will represent an important and considerable research effort with the main objective of developing a new seismic imaging system at NORSAR. Recorded or synthetic data will be input to the imaging system in order to generate target-oriented depth images of the ground structures detected by elastic waves. The imaging or migration methods to be used and further developed, are ray tracing based, i.e., classified among Kirchhoff summation approaches, as opposed to wave-equation methods. Such Ki rchhoff methods need Green's functions (traveltimes, amplitudes, etc) to correct for wave propagation effects between all sources and receivers, and all points of the target zone to image. The key method to compute ray tracing based Green's functions will be the 3D Wavefront Construction (WF3D) ray tracer developed by NORSAR since 1993 and now part of the commercial modelling package. WF3D is indeed used by the industry for imaging purposes. The existing WF3D tracer will therefore be adapted for a more ef ficient and flexible use in imaging, and interpolation techniques will be studied to allow coarser grids of Green's function. The on-going developments of WF3D towards complex anisotropy will also be a fundamental basis for imaging. Another class of metho ds to be used for Green's funtions are Eikonal solvers, to complete WF3D with first-arrivals. A second key element of ray tracing modelling is an adequate model. There is indeed a need for a more flexible type of model, including a new dimension, i.e., th e possibility to easily perturbe the model, which is important for integrating modelling, tomography and imaging, as all these steps are needed in a complete inversion approach. Efficient and modelling-based data access to large files on hard disks is als o a necessity for target-oriented imaging. At last, modelling by demigration will be studied too because such techniques are closely related to imaging and will significantly extend the modelling tools of NORSAR.