Noise and artifacts often strongly influence the resolution of depth images obtained with standard migration algorithms. In this thesis a new method of seismic imaging was applied to two marine data sets acquired during the CINCA experiment in 1995: The Fresnel Volume Migration. A comparison between the latter and Kirchhoff Prestack Depth Migration was performed to discuss the additional structural details extracted with the help of Fresnel Volume Migration.
Fresnel Volume Migration is based on the idea of restricting the migration operator in a form that the resulting image of a recorded event is limited to the volume in the subsurface that physically contributes to the reflected signal. The Fresnel volumes were calculated using the paraxial ray method. The ray tracing algorithm required information about the emergence angles of the waves arriving at the receivers. A multichannel cross-correlation technique was used to estimate the horizontal slowness sections which comprise the necessary emergence angle information. Several input parameters were studied with the aim to obtain the best images as well as to reduce the computing time.
The comparison of the Kirchhoff images with the corresponding Fresnel images of line SO104-07 and, respectively, of line SO104-13 showed a noticeable improvement of the images after Fresnel Volume Migration. A strong suppression of the migration artifacts due to the limitation of the migration operator was demonstrated as well as the reduction of the noise level within the resulting Fresnel images. Thrust faults have been identified after Fresnel Volume Migration in a region where normal faulting due to plate bending was expected. The complex internal structure of the frontal prism at the trench was analyzed and discussed. The intra-plate boundary itself was imaged down to approximately 12 km depth on both lines as well as a downward continuation of the ocean bottom structures underneath the continental slope. Plate parallel faults were observed and interpreted to mark the upper boundary of the
subduction channel. In the case of a horst-continent collision, strong compressional forces may occur, possibly resulting in an eastward movement of parts of the overriding plate. The Fresnel images gave an excellent and detailed insight into the normal fault systems along line SO104-07 and also along line SO104-13. Reflections below these normal faults suggested a detachment.
The application of the Fresnel Volume Migration method to the marine data sets enabled to visualize certain details of the subsurface within the investigation areas which are not observable in the Kirchhoff images.
Falls Ihr Browser eine Datei nicht öffnen kann, die Datei zuerst herunterladen und dann öffnen.