Velocity structure of a bottom simulating reflector offshore Peru: Results from full waveform inversion

Earth and Planetary Science Letters
By: , and 

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Abstract

Much of our knowledge of the worldwide distribution of submarine gas hydrates comes from seismic observations of Bottom Simulating Reflectors (BSRs). Full waveform inversion has proven to be a reliable technique for studying the fine structure of BSRs using the compressional wave velocity. We applied a non-linear full waveform inversion technique to a BSR at a location offshore Peru. We first determined the large-scale features of seismic velocity variations using a statistical inversion technique to maximise coherent energy along travel-time curves. These velocities were used for a starting velocity model for the full waveform inversion, which yielded a detailed velocity/depth model in the vicinity of the BSR. We found that the data are best fit by a model in which the BSR consists of a thin, low-velocity layer. The compressional wave velocity drops from 2.15 km/s down to an average of 1.70 km/s in an 18m thick interval, with a minimum velocity of 1.62 km/s in a 6 m interval. The resulting compressional wave velocity was used to estimate gas content in the sediments. Our results suggest that the low velocity layer is a 6-18 m thick zone containing a few percent of free gas in the pore space. The presence of the BSR coincides with a region of vertical uplift. Therefore, we suggest that gas at this BSR is formed by a dissociation of hydrates at the base of the hydrate stability zone due to uplift and subsequently a decrease in pressure.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Velocity structure of a bottom simulating reflector offshore Peru: Results from full waveform inversion
Series title Earth and Planetary Science Letters
DOI 10.1016/0012-821X(95)00242-5
Volume 139
Issue 3-4
Year Published 1996
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Earth and Planetary Science Letters
First page 459
Last page 469