Acoustic and Shear-Wave Velocities in Hydrate-Bearing Sediments Offshore Southwestern Taiwan: Tomography, Converted Waves Analysis and Reverse-Time Migration of OBS Records
Resource
Terrestrial, Atmospheric and Oceanic Sciences 17 (4): 757-779
Journal
Terrestrial, Atmospheric and Oceanic Sciences
Journal Volume
17
Journal Issue
4
Pages
757-779
Date Issued
2006
Date
2006
Author(s)
Abstract
A 2.5-D combined seismic reflection and refraction survey has been conducted in the accretionary complex offshore of southwestern Taiwan where BSRs (Bottom Simulating Reflectors) are highly concentrated and geochemical signals for the presence of gas hydrate are strong. In this study, we perform velocity analysis of the 6 4-component OBS (Ocean-Bottom Seismometer) records along the southernmost transect of this seismic experiment. We utilize 3 independent methods in order to accurately determine the acoustic and shear-wave velocities of the sediments: 1-D Root Mean Square (RMS) analysis of the P-P and P-S reflected events on individual datumed components, 2-D inversion of the P-P and P-S reflected and refracted events along the in-line transect, and 3-D acoustic inversion of the first arrivals. The principal sources of bias in the determination of the velocities are the 3-dimentional nature of the topography and the complexity of the underlying structures. The three methods result in consistent velocity profiles. Rapid lateral and vertical variations of the velocities are observed. We then investigate the large scale gas hydrate content through rock physic modeling: at the vertical of each OBS, shear-waves velocities are utilized to estimate the water-filled porosities, and the acoustic velocities predicted for a set of gas hydrate, quartz and clay contents are compared to the observed profiles.
Subjects
Acoustic and shear-wave velocities; Gas hydrates; Ocean Bottom Seismometers
SDGs
Other Subjects
acoustic wave; marine sediment; modeling; S-wave; seismic method; seismic reflection; seismic tomography; seismic velocity; seismometry; velocity profile; velocity structure; Asia; Eurasia; Far East; Taiwan
Type
journal article
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