Akademik Veri Yönetim Sistemi
American Geophysical Union 2023 (AGU 2023), California, Amerika Birleşik Devletleri, 11 - 16 Aralık 2023, ss.1, (Tam Metin Bildiri)
The Lord Howe Rise (LHR) located at the eastern offshore of Australia is considered to be a fragment of continental crust that separated from East Gondwana when the Tasman Sea opened. The detailed seismic structure of the sediments and the topmost basement are key to understanding the rifting history of the LHR. To reveal this history, we need an accurate velocity model that describes the subsurface rock properties. Full waveform inversion (FWI) is an effective inversion method that estimates the velocity model by reducing the residual errors between the observed and calculated of waveforms. In this study, we applied FWI to 2-D marine wide-angle seismic data acquired with ocean-bottom seismographs (OBS) and airgun shots from the LHR which were collected with R/V KAIREI in the year of 2017 by the Japan Agency for Marine-Earth Science and Technology. There were 64 OBSs deployed along the profile in total on the ~223 km-long survey line to reveal the regional velocity structure. To obtain a high-resolution velocity model, we used 42 OBSs that were deployed densely with 800 m spacing and 225 airgun shots with 200 m intervals along ~45 km in the middle of the survey line.
Since the study area contains complex structural features, it is difficult to acquire a velocity model with the conventional velocity analyzing techniques, such as traveltime tomography (TT), even though using the dense OBS data. By applying the FWI method, we acquired a high-resolution subsurface velocity model which is well matched with our multi-channel seismic (MCS) reflection image through the spatial variation. The oblique reflections depth of ~6-7 km, the shallow sediment layers depth of 2 km, and the rift basin depth of 3 km on the MCS reflection image, are successfully matched and imaged on the FWI velocity model. In the shallow part of the sedimentary basin the velocity reversal extending in the layers, which corresponds to a strong horizontal reflection on the MCS reflection image, is successfully observed on the FWI velocity model.
Compare to the result by TT, the FWI velocity model shows a significant improvement in the spatial resolution. The final FWI velocity model will be useful to infer regional physical properties for geological interpretation in the middle of the LHR and will be useful to discuss the tectonic history based on the obtained seismic structure.