Tectonic and sedimentary controls on widespread gas emissions in the Results from systematic, shipborne multibeam echosounder water column imaging

S. Dupré1, C. Scalabrin1, C. Grall1,2, J.-M. Augustin1, P. Henry2, A.M.C. Şengör3, N. Görür3, N. Çagatay3 and L. Géli1

1 IFREMER, Marine Geosciences, Plouzané, France - [email protected] 2 CEREGE, Marseille, France 3 Technical University,

Study Seepage, faulting and seismic activity ?

 What can we learn from gas escapes in terms of tectonic and seismic activity? Objectives  How do expulsion of fluids and fluxes evolve through time and space prior and after a seismic event? 1) Establish an accurate spatial distribution of the seeps at the scale of the entire sea of Marmara • Gas seeps may be triggered by earthquakes

2) Investigate the relationship with the fault network (active and inactive faults) • Occurrence / increase of gas: California (Field and Jennings 1987) and the sedimentary environment (nature, thickness and related-processes) Gulf of Patras (Christodoulou et al 2003) Gulf of Izmit (Kuscu et al 2005) • Non-seismic events recorded with OBS related to gas escape through the seabed Means  Sea of Marmara (Tary et al. 2012, Bayrakci et al. 2014)

• 3D acoustic imagery of the water column with ship-borne multibeam echosounder 1 km Cold seeps and active faulting in the Sea of Marmara  Simrad EM302 (27-33 kHz) on the R/V Le Suroît • Occurrence of numerous fluid emissions at the seabed: Marmarascarps 2002,  New and wide-coverage dataset Marnaut 2007 (Zitter et al 2008)  21 full days acquisition / 4500 km track lines ≡ 2900 km2 = 70% SoM (wd>300m  1270 m) • Acoustic detection of fluid escapes: SAR side scan sonar/180kHz (2000), • 2009 Marmesonet marine expedition, part of the ESONET EK60/38kHz (2007), EM302/30kHz (2009) (Géli et al 2008; Dupré et al 2015) (European Seas Observatory NETwork) demonstration mission (MarmaraDM) Géli et al 2008 • Fluid emissions at the seabed of the Sea of Marmara associated with gas bubbles, Near-bottom pictures from submersible (Marnaut 2007 expedition) (brackish) water and oil with authigenic carbonates

Geological setting Multibeam water column processing, vizualisation and analysis

Active tectonics in the Sea of • Along the right lateral strike-slip NAF Significant efforts to develop tools for the post-acquisition chain • Fast motion of the Anatolian Plate (>20 mm/y) • display, replay, processing and analysis dataset • High deformation rates • software platform combining Sonarscope a Matlab based program and a 3DViewer called Sonarscope3DViewer, both Ifremer softwares

Armijo et al 1999, Reilinger et al 1997 Algorithms developed to: • replay and process the polar echograms by improving the signal to noise ratio Structural map of the Sea of Marmara • pick up events in the water column (e.g. root flares on the seabed) • Fault network dominated by strike-slip and normal faulting • accurately localize these events • Debate on current tectonic regime in the SoM • echo-integrate the signal Pure strike-slip • integrate multidata in 3DViewer (©Ifremer) and GIS software Pull apart basin Extension in Aegean Sea • Divided in subbasins and structural highs Case study: the Sea of Marmara • Gas bubble echoes very well detected within the entire water depth range Seismic activity • Most of the anomalies caused by gas bubbles emitted from the seabed Sonarscope - 3DViewer(© Ifremer) • High-magnitude earthquakes in a highly populated area • Intense and widespread gas emissions 7.4-magnitude 1912 Ganos / 1999 Izmit • Shallow focal depths < 20 km (Sato et al 2004) R/V L’Atalante not to scale Bathymetry map from Le Pichon et al 2011, Rangin et al 2001 Ambraseys and Jackson 2000 Fault network by Grall et al 2012 with caution on localisation of events prior to 1900

Spatial distribution of gas seeps Controls on fluid emissions in the Sea of Marmara At the scale of the basins and highs At the scale of the Sea of Marmara  Connections to the gas sources Acoustic gas distribution prior 2009: 2000 2007

 Tectonic control

• Gas seeps commonly observed along - Known fault scarps - The major portion of the Main Marmara Fault (mainly concentrated in the northern part of the SOM / northern branch of the NAF) - The edges of the four deep basins (whether or not they are in relation to the main current fault trace of the MMF) - In relation to topographic highs, i.e. to the anticlines acting as gas traps

EM302 3D water column surveys 2009 (in relation to the distributed deformation, expressed as folds and minor faults and locally with sediment mobilization processes)

• Fault network - Main Marmara Fault system and inherited faults - Relation between fault activity and seepage far from being linear even if most of the seeps follow traces of active faults Clusters of gas emissions on the Western and Central Highs

 Sedimentary control

• Nature and thickness of the sediments wherever unfaulted and undeformed, thick impermeable layers prevent gas from migrating

• Deformation, destabilization and erosion processes Δz = 40m Deformation, either resulting from tectonic faulting or from slope instability Deformation – faults and folds of the sediment cover Erosional features: scars of the sediment cover induced by gravity slumping or mass-transport deposits

The absence of gas at the seabed may be explained by the sedimentary architecture and the physico- chemical conditions of the sediments. Fig. Shaded 3D high-resolution bathymetry view of a slide scar located in the Central High in the Sea Of Marmara at ~660 m waterdepths. The seafloor multibeam data indicate that the failure removed ~40m (± 5m) of sediments at the location of the core. This is in good agreement with the stratigraphy and the lithology of the recovered core. Red spot and tick stand for the location of the core MET09GR02 in both maps. References Yellow circles:  seafloor depressions  destabilized upper sediment cover This study has been published in:  high-backscatter seabed amplitudes  water column acoustic gas emissions Dupré S, Scalabrin C, Grall C, Augustin AH, Henry P, Şengör AMC, Görür N, Çağatay N, Géli L (2015) Tectonic and sedimentary controls for widespread • Intense and widespread seepage mainly gas emissions in the Sea of Marmara. Results from systematic, shipborne  Along the Main Marmara Fault multibeam echosounder water column imageries. Journal of Geophysical  At anticlinal structures Research 120 (5):2891-2912. doi:10.1002/2014JB011617  At the edges of the sedimentary basins Cited references therein. • Restricted gas emissions  Within the basins Perspectives  Along some segments of the MMF: Kumburgaz and North Çınarcık segments This study highlights the importance of measuring long-term multiparameter • Temporal variability of gas emissions time-series (with seafloor observatories), including gas escape monitoring at  Broad range of time scales: minute to year selected sites Microearthquake epicentres (yellow dots) recorded between 2005 and 2011 Sengör et al 2014; pers. comm. from Hayrullah Karabulut, 2014  Persistent activity -first order-  to understand the fluid emission activity with regard to the micro-seismicity  Change observed in Tekirdağ and Çınarcık basins unlike the inner SOM cycle (and seismic activity)  Locally: lateral fluid migration?

Links between gas emissions and (micro)-seismicity? Geological implications at a regional scale and significance of the absence of gas emissions along Relationship with the Basin: connections with the gas sources some short segments of the Main Marmara Fault • Underlying Eocene Thrace Basin, a well known and prolific gas province  Gas emissions are mostly associated with active faults rather than inactive ones • Geochemical evidence in the Western High (Bourry et al 2009; Ruffin et al 2012)  Most of the swarms of micro-seismicity characterized by numerous, densely spaced gas emission sites • Genetic relationship between onshore and offshore gas emissions could help (gas accumulations along the MMF in the WH could reflect the current high level of micro-seismicity) delimit the Thrace Basin gas province in the Sea of Marmara  In contrast, the Istanbul-Silivri and the Prince of Islands segments are characterized by a relative absence of micro-seismic activity • Proposed scenario: Thrace Basin province could be bound by the Main Marmara These segments record little or even no gas emissions at the seabed: Fault as it crosses the Western High and the Central Basin, and by the southern -the 5 km-long segment connecting the CH to the KB and eastern borders of the Central High -the 5 km-long segment at the northern border of the Çınarcık Basin -a relative smaller density of gas emissions observed east of the segment across the CH and along the northern border of the KB • Further geochemical characterization of emitted fluids (MARSITE) Le Pichon et al 2014  There, the absence of fluid emissions can not be related to an absence of sources below or to sedimentary loading. We argue for a strong correlation between the occurrence of gas emissions and the present-day micro-seismic activity. Relationship to the pre-Quaternary Marmara shear zone and contribution to the understanding of the tectonic evolution of the Marmara Region Proposed scenario: the absence of earthquake-induced ground shaking is the primary factor responsible for the relative absence of gas emissions along the Istanbul-Silivri segment and part of the Princes Islands segment The distribution of gas emissions underlines a buried, complex fault network inherited from the tectonic history of the Marmara region The Istanbul-Silivri segment : Pondart et al 2007, Bohnhoff et al 2013 vs Ergintav et al 2014 continuous creep The Princes Islands segment: Ergintav et al 2014: locked segment