浅层结构不确定性对广角地震走时正演模拟结果的影响——以西沙地块OBS2011-1测线为例

doi:10.6038/cjg2021O0474

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Abstract In marine geophysical exploration, multi-channel seismic (MCS) data are often used to establish shallow layer model. Wide-angle ocean bottom seismometer (OBS) data are then used for ray-tracing the seismic traveltime and inverting the crustal structures. Due to limitation of data acquisition, some OBS profiles lack of synchronously collected MCS data, which causes a great uncertainty on the shallow structure in the model and may influence the reliability of the forward modeling. To assess the uncertainty, synthetic models were built and theoretical traveltimes were calculated by RayInvr software to study how the thickness and velocity uncertainty of the sedimentary layer influence the forward modeling results. For comparison, a MCS profile MCS2019-3 were used to built the shallow structure model, based on which the P-wave velocity of profile OBS2011-1 was re-modelled. By comparing with the previous results, it shows that the thickness and velocity uncertainty of the sedimentary layer have great influence on the shallow structures but a little influence on the structures at depth. Wrong sedimentary velocities and basement depths can also successfully fit the PsP phases, but the Pg, PmP and Pn phases in the crust and top mantle will have small traveltime fluctuation. The increased traveltime is due to the larger sedimentary velocity and thickness, while the decreased traveltime is due to the smaller velocity and thickness. In the absence of the PsP phase, different velocity-depth combinations can still well fit the other seismic phases, but will increase the uncertainty of the results.

Key words： Ocean bottom seismometer Velocity structure Forward modeling Xisha block

Received: 07 December 2020

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P738

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http://www.geophy.cn//EN/10.6038/cjg2021O0474 OR http://www.geophy.cn//EN/Y2021/V64/I10/3669

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