Quantifying Gas Within the Elkhorn Slough Sediments, Central California

Abstract:

The occurrence of shallow gas in coastal environments is not uncommon. In central California, the Elkhorn Slough has been recently studied through seismic analysis, in order to acquire an understanding of its infill during the last thousands of years. Within those seismic units, the occurrence of gas (acoustic turbidity) is widespread in the central and upper slough. The depth of these gas pockets range from 5m below the channel floor to almost the surface. We have been monitoring the area for the last years completing the acquisition this year, running multiple seismic surveys to track the gas occurrences and attempt to quantify them. In a few areas, there is also strong evidence of gas seepage (acoustic plumes) directly above the interpreted gas pockets. A few push corers were recently taken to groundtruth the seismic data. We discuss these gas accumulations and seepages, their relationship with the seismic units, the tidal regime, the different seismic source frequencies, and the implications of the gas seepage in the water column and possibly the atmosphere of this fragile environment.

Acknowledgments: CSUMB (chirp source), ESNERR staff, and the EART102 Spring 2015 class. The Non-Senate Faculty Professional Development Award 19900-433332-ESGARC and ONR grant N00014-14-1-0172 supported this research.