HR: 14:10h
AN: S43C-03    [Abstracts]
TI: High-resolution crustal seismic imaging from OBS data by full-waveform inversion: application to the eastern-Nankai trough
AU: * Operto, S
EM: operto@geoazur.obs-vlfr.fr
AF: Geosciences Azur CNRS-IRD-UNSA-UPMC Observatoire Oceanologique de Villefranche sur mer, La Darse BP 48, Villefranche sur mer, 06230 France
AU: Virieux, J
EM: viri@geoazur.unice.fr
AF: Geosciences Azur CNRS-IRD-UNSA-UPMC Observatoire Oceanologique de Villefranche sur mer, La Darse BP 48, Villefranche sur mer, 06230 France
AU: Dessa, J
EM: dessa@geoazur.obs-vlfr.fr
AF: Geosciences Azur CNRS-IRD-UNSA-UPMC Observatoire Oceanologique de Villefranche sur mer, La Darse BP 48, Villefranche sur mer, 06230 France
AB: In offshore surveys, the deep crust is generally investigated by traveltime tomography applied to coarse Ocean Bottom Seismometer (OBS) data.The inferred velocity models are of limited resolution precluding a quantitative analysis of deep tectonic discontinuities. If densely sampled OBSs can be deployed, the resulting dataset becomes amenable to full-waveform processing which should lead to a significant resolution improvement. Such full-waveform processing has been applied to the eastern-Nankai subduction zone. Full-waveform processing is entirely implemented in the frequency domain, enabling efficient finite difference wave modelling for multiple sources and allowing to limit the inversion to a few discrete frequencies of increasing value. Such a hierarchical procedure defines a multi-resolution approach to seismic imaging. The dataset was recorded by 93 instruments deployed along a 105 km long profile. Thirteen frequencies ranging from 3 Hz to 15 Hz were inverted sequentially and 20 iterations per frequency were computed. The maximum vertical resolution in the deep crust was around 1 km while the resolution of traveltime tomography is of the order of 10 km. Full-waveform tomography imaged an intense compressive regime in the backstop evidenced by several thrusts corresponding to negative velocity anomalies. The subducting Paleo-Zenisu ridge is also reconstructed, the top of which marks a clear decollement level. Velocities in the upper mantle beneath the ridge are rather low (7.5 km/s) suggesting partially serpentinized mantle beneath the ridge. This paper demonstrates the feasibility of full-waveform tomography applied to dense OBS dataset to quantitatively image the entire crust with a tremendous resolution improvement compared to what is usually obtained from traveltime tomography.
DE: 0902 Computational methods: seismic
DE: 0935 Seismic methods (3025, 7294)
DE: 3260 Inverse theory
DE: 3285 Wave propagation (0689, 2487, 4275, 4455, 6934)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Seismology [S]
MN: Fall Meeting 2005