Conference proceeding
Gas evidence and seepage; implications and subsidence in the Elkhorn Slough, CA
American Geophysical Union Fall Meeting, Vol.2013
Dec 2013
Abstract
The presence of gas pockets underneath the sediments of the Elkhorn Slough, a 10-km long, 1200-hectare tidal estuary located in Monterey Bay, has been imaged for the first time. Seismic surveys were run in 2011-2012 with an EdgeTech SB-424 full-spectrum sub-bottom CHIRP profiler, used with a default pulse which generates a sweep frequency of 4 kHz-24 kHz for 10 ms, and a vertical resolution of 0.4 m. This system performed ideally in this shallow environment. Preliminary interpretation of the data shows multiple and widespread evidence of gas as acoustic blanking, acoustic turbidity, and acoustic plumes. The interpreted gas affects the sedimentary column from 5 m below the present channel all the way up to the surface. The gas front of these pockets is buried under the last two seismic units below the channel floor, and in some cases, reaches the surface of the sedimentary column. There are also indications of seepage from these pockets towards the water column, suggesting the seal is no longer effective. Multiples cores were taken between 2008 and 2011 and they confirm the presence of methane (as well as gas cracking evidence in XRays). The areas with unstable methane gas affect this delicate environment, which is currently under a watch for subsidence and strong erosion. The gas seepage can be triggering further collapse of sediments and enhancing the subsidence. In the present work we discuss these factors as well as aim to quantify how much gas the Slough sediments hold and how much is escaping at present.
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Details
- Title
- Gas evidence and seepage; implications and subsidence in the Elkhorn Slough, CA
- Creators
- A. Garcia-Garcia - University of California Santa Cruz, Earth and Planetary Sciences Santa Cruz, CA USA United StatesN. KingH. SimsM. LopezM. D. LeveyGeoff ShiptonElizabeth B. WatsonRon EbyAnonymous
- Publication Details
- American Geophysical Union Fall Meeting, Vol.2013
- Conference
- American Geophysical Union Fall Meeting (2013)
- Publisher
- American Geophysical Union
- Resource Type
- Conference proceeding
- Language
- English
- Academic Unit
- Biodiversity, Earth, and Environmental Science (BEES)
- Identifiers
- 991019298621804721