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Geophysical Journal International 190, 2 (2012) 993-1007
Microevents produced by gas migration and expulsion at the seabed: A study based on sea bottom recordings from the Sea of Marmara
J.-B. Tary ( ) 1, 2, L. Geli 2, Claude Guennou 3, P. Henry 4, Nabil Sultan 2, Namik Cagatay 5, Valérie Vidal 6
(04/07/2012)

Different types of 4-component ocean bottom seismometers (OBS) were deployed for variable durations ranging from 1 week to about 4 months in 2007, over soft sediments covering the seafloor of the Tekirdag Basin (western part of the Sea of Marmara, Turkey). Non-seismic microevents were recorded by the geophones, but generally not by the hydrophones, except when the hydrophone is located less than a few tens of centimetres above the seafloor. The microevents are characterized by short durations of less than 0.8 s, by frequencies ranging between 4 and 30 Hz, and by highly variable amplitudes. In addition, no correlation between OBSs was observed, except for two OBSs, located 10 m apart. Interestingly, a swarm of ∼400 very similar microevents (based on principal component analysis) was recorded in less than one day by an OBS located in the close vicinity of an active, gas-prone fault cutting through the upper sedimentary layers. The presence of gas in superficial sediments, together with analogies with laboratory experiments, suggest that gas migration followed by the collapse of fluid-filled cavities or conduits could be the source of the observed microevents. This work shows that OBSs may provide valuable information to improve our understanding of natural degassing processes from the seafloor.
1 :  University of Alberta, Canada
University of Alberta
2 :  IFREMER centre de Brest
Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)
3 :  Domaines Océaniques
INSU – Institut d'écologie et environnement – Institut Universitaire Européen de la Mer (IUEM) – Université de Bretagne Occidentale (UBO) – Observatoire des Sciences de l'Univers – CNRS : UMR6538
4 :  Centre européen de recherche et d'enseignement de géosciences de l'environnement (CEREGE)
CNRS : UMR6635 – Institut de recherche pour le développement [IRD] – INSU – Université de Provence - Aix-Marseille I – Université Paul Cézanne - Aix-Marseille III
5 :  ITU (GEOLOGY AND MINING DEPARTMENT)
Istanbul Technical University
6 :  Laboratoire de Physique de l'ENS Lyon (Phys-ENS)
CNRS : UMR5672 – École Normale Supérieure (ENS) - Lyon
Planète et Univers/Sciences de la Terre/Géophysique

Physique/Physique/Géophysique

Sciences de l'environnement/Milieux et Changements globaux
Body waves – Gas and hydrate systems – Interface waves – Seismic attenuation – Time series analysis – Wave propagation
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GJI-Tary-2012.pdf(1.3 MB)