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| | Abstract | | Acoustic waveform tomography was applied to wide-angle Ocean Bottom Seismograph data acquired in the seismogenic Nankai subduction zone. To reduce artifacts arising from elastic effects, the inversion focused on early arrivals, and was conducted in two steps, 1. fitting phase information, and 2. the incorporation of amplitude information. Image sources were used to simulate the source ghost. The receiver ghost was filtered out during preprocessing. Our image successfully retrieved major geological features such as lithological boundaries such as fore-arc basin and plate boundaries and low velocity layers. The mega splay fault responsible for past earthquake rupture propagation was delineated with remarkable clarity, and showed the contact with the proximate fluid-filled low velocity layer. The results do not only coincide with prestack migration images, and migration velocity analysis, but also demonstrate that waveform inversion is able to utilize diving waves and wide-angle reflections to illuminate the region ambiguous with reflection methods. |
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