Shallow gas seismic structures: forms and distribution on Santa Catarina Island, Southern Brazil

Authors

  • Antonio Henrique da Fontoura Klein Universidade Federal de Santa Catarina; Laboratório de Ocanografia Costeira
  • Larissa Felicidade Werkhauser Demarco Instituto de Pesquisas Tecnológicas do Estado de São Paulo
  • Vanessa Guesser Universidade Federal de Santa Catarina; Laboratório de Ocanografia Costeira
  • Gabriela Reis Flemming Universidade Federal de Santa Catarina; Laboratório de Ocanografia Costeira
  • Jarbas Bonetti Universidade Federal de Santa Catarina; Laboratório de Ocanografia Costeira
  • Diego Porpilho Universidade Federal de Santa Catarina; Laboratório de Ocanografia Costeira
  • Arthur Ayres Neto Universidade Federal Fluminense
  • Jorge Antonio Guimarães de Souza CB&I
  • Cesár Alexandre Félix EGS Brasil

DOI:

https://doi.org/10.1590/s1679-87592016115506404

Keywords:

Shallow gas features, High resolution seismic, CHIRP, Gas-charged sediments

Abstract

This paper presents the spatial distribution of shallow gas structures and classifies them on the basis of two different data sets of CHIRP seismic records, one from the Conceição Lagoon (CL) and the other from North Bay (NB), both on Santa Catarina Island, Southern Brazil. Side scan sonar data from the CL were used to facilitate the understanding. The sub bottom (SB) seismic data were processed and interpreted by means of the SeisPrho software, the side scan sonar (SSS) data by SonarWiz5 software and the spatial extension being measured with the help of GIS. The shallow gas structures were defined in accordance with their shapes in the seismic recordings (echo-character). At the CL, shallow gas accumulations were found in the form of seepages and features presenting shallow gas structures between the surface and 8.20 ms (around 12.3 m). Accumulations of gas were found in the form of Acoustic Blanking with Acoustic Plume, and also Black Shadows. Pockmarks were found on the lagoon floor and associated with gas seepages (average size diameter 0.97 ± 0.19 m and density from 54 to 242 units per 50 m2). In the NB three types of shallow gas features were found in the seismic profile, namely Acoustic Blanking, Turbidity Pinnacles and Intra-sedimentary plumes. The depth varied from the surface to 12.10 ms (around 18.15 m). In both environments, the gas is escaping from the sediment into the water column. The Pockmarks in the CL and the Acoustic Plume features and sediment rich in total sulfur in the NB validate these findings.

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Published

2016-12-01

How to Cite

Klein, A. H. da F., Demarco, L. F. W., Guesser, V., Flemming, G. R., Bonetti, J., Porpilho, D., Ayres Neto, A., Souza, J. A. G. de, & Félix, C. A. (2016). Shallow gas seismic structures: forms and distribution on Santa Catarina Island, Southern Brazil. Brazilian Journal of Oceanography, 64(4), 325-338. https://doi.org/10.1590/s1679-87592016115506404

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Section

Original Article