DEEP STRUCTURES BENEATH THE MICHIGAN BASIN FROM REPROCESSED COCORP DATA: SEISMIC RAY THEORY AND ITS APPLICATION IN REFLECTION SEISMOLOGY (VELOCITY INVERSION, INHOMOGENEOUS MEDIA)

A careful application of data processing techniques, including deconvolution and velocity filtering before stack and more detailed velocity analysis, to COCORP (Consortium for Continental Reflection Profiling) data from central Michigan has resulted in greatly improved imaging of a previously reported Keweenawan rift buried beneath the Paleozoic of the Michigan Basin. This improved image provides significant new information on the structure and evolution of the Keweenawan rift. Furthermore, the reprocessed data also reveal other deep structures unrecognized in previous interpretations, including a deeply penetrating reflection which may represent a major crustal fault and possible weak reflection bands from mid-crustal (25 km) and Moho (43 km) depths.; Another important aspect of data processing is to determine subsurface velocity structure. A new traveltime inversion scheme based on asymptotic ray theory (ART) is presented to estimate velocities and interface geometries of two-dimensional media from deep reflection data. Experiments with both synthetic and COCORP data indicate that this method is effective and can produce better results than routine methods for determining subsurface velocities. To further aid seismic interpretation, a fast algorithm based on ART is also included in the inversion scheme for calculating synthetic seismograms for a velocity model estimated from traveltime data.; Seismic modelling is an important aid in the interpretation of deep reflection data. A new ray-Kirchhoff method is developed for modelling body waves in laterally inhomogeneous media which extends the applicability of simple ray theory to caustics and other diffraction phenomena and is valid in both slowly and rapidly varying media. This method also provides a useful means for seismic migration in laterally inhomogeneous media. To implement the method efficiently, a perturbation scheme is proposed which avoids most of the ray tracing for computing wavefields in media with weak lateral variations. New techniques are also presented for avoiding caustics and foci on an intergral surface used in the method.