Microevents produced by gas migration and expulsion at the seabed: a study based on sea bottom recordings from the Sea of Marmara

Type Article
Date 2012-08
Language English
Author(s) Tary Jean-Baptiste1, Geli LouisORCID1, Guennou Claude5, Henry Pierre2, Sultan NabilORCID1, Cagatay N.3, Vidal V.4
Affiliation(s) 1 : IFREMER, Dept Marine Geosci, F-29280 Plouzane, France.
2 : Aix Marseille Univ, CEREGE, CNRS, UMR 6635, F-13545 Aix En Provence 4, France.
3 : Istanbul Tech Univ, Min Fac, Dept Geol, TR-34469 Istanbul, Turkey.
4 : Univ Lyon, Phys Lab, Ecole Normale Super Lyon, CNRS, F-69364 Lyon 07, France.
5 : Univ Western Brittany, UMR 6538, European Inst Marine Studies IUEM, F-29280 Plouzane, France.
Source Geophysical Journal International (0956-540X) (Wiley-blackwell), 2012-08 , Vol. 190 , N. 2 , P. 993-1007
DOI 10.1111/j.1365-246X.2012.05533.x
WOS© Times Cited 19
Keyword(s) Time series analysis, Gas and hydrate systems, Body waves, Interface waves, Seismic attenuation, Wave propagation
Abstract 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 similar to 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.
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