Title: Pierre Henry, Tiphaine Zitter, Fabienne Fornacciari, Louis Geli Collge de France, Chaire de Godynami
1Cold seeps along the Main Marmara Fault context
and perspectives for monitoring.
- Pierre Henry, Tiphaine Zitter, Fabienne
Fornacciari, Louis Geli Collège de France,
Chaire de Géodynamique, Trocadéro, Europôle de
lArbois BP80, 13545 Aix-en-Provence, France
Ifremer, BP 70, 29280 Plouzané, France - Data sources Marmara1 (Suroît) cruise
bathymetry and HR seismics - Marmacore, MarmaraVT (Marion-Dufresne) coring
- Marmarascarps (Atalante and Victor ROV)
observation, microbathymetry, THR. - Content Cold seep distribution along the active
fault(s) - Hydrogeological systems importance of the
lacustrine past - Understanding the evolution with time
- Response to strain exemples from subductions
- Marnaut cruise in 2007
- ESONET observatory project
http//www.cdf.u-3mrs.fr/henry/marmara/index.html
2Marmara Sea
- Following the Kocaeli earthquake, many gas
seepages have been observed on the sea bed. The
most prominent of them was one about one km NW of
Topçular where significant gas bubbles have been
observed on the sea surface. - Gas plumes are observed on the echo-sounder.
They are sometimes very thick and diverted from
vertical by currents. - It is well-known that the subaquaeous
sedimentary units in the Izmit Bay are charged
with gas and the Holocene postransgressional
marine deposits act as a cap layer. The
gas-charged sediments are generally placed in the
central parts of the basins where the gulf
becomes wider. - From Bedri Alpar, Turkish Journal of Marine
Sciences, 5 (3), 1999, "Underwater signatures of
the Kocaeli earthquake,(August 17th 1999)",
111-130. http//www.geocities.com/CapeCanaveral/St
ation/8361/Quake99Turkey.html
3Cold seeps a consequence of methane
(hydrocarbon) release in seawater and/or
oxidation at a shallow depth in the sediment
- Examples from Marmara Sea - Marmarascarps Cruise
Black Patches
Bacterial Mats
Carbonate crusts
Bubble emission
Brackish water emission
4Cold seep distribution in Marmara Sea
- Mostly based on ROV observations during
Marmarascarps cruise - All known seeps are on strike-slip fault traces
- Most, but not all fault segments explored have
cold seeps (black patches bacterial mats) - A few sites display highly focused flow
- Brackish water expulsion
- Methane free gas migration in the sediment
ROV visual observation track
Black patches
Authigenic carbonates
Active chimneys
Bacterial mats
Fault
5Marion Dufresne Cores (MARMARA VT, Mai 2004)
- Pore fluid sampling
- Determine past Marmara water composition
- Composition of expelled fluids, flow pathways and
flow rates - Tectonics and sedimentology
- Connexion Aegean-Marmara Sea-Black Sea
http//www.cdf.u-3mrs.fr/henry/marmara/index.html
6Central basin gas plume in sediment
- Geophysical evidence for free gas (3.5 kHz chirp)
- No geochemical evidence for pore water advection
(MD04-2742) - Carbonates and bacterial mats at fault outcrop
7Tekirdag basin chimneys Brackish water outflow
- Active chimneys aligned on fault rupture (ROV
micro bathymetry) - Near outlet of canyon
Zone of disturbed echo gas charged sand layers
8Tekirdag basin chimneys kilometer scale flow
cell
N
S
1 km
marine
lacustrine
thick sand layers
- Thick sand layers (gt 1m) in lacustrine section
contain low salinity pore fluid - Stronger gradient at MD04-2740 than at MD04-2737
is evidence for lateral flow toward the fault
zone
9Smaller scale flow cells influence on
sulfate-methane reaction
- Transient methane migration following earthquake
1063 A.D. (Halbach et al., 2004) - Model is too circumstantial and does not explain
chloride profiles - Steady state convection driven by salinity
difference (Henry et al. 1992, 1996) - Minimum permeability required is very high for
marine clay-rich mud (10-14 m2) - Episodic bubble expulsion drives seawater entry
(Tryon et al., 2002) - Bubble emission maintains high permeability
conduits
10A relationship between seawater intrusion and
methane oxidation
11Factors influencing localized pore fluid expulsion
- Driving forces
- Buoyancy from salinity contrast
- Compaction
- 2-phase flow gas generation, migration and
expulsion - Conduits
- Coarse turbidites gt lateral flow toward fault
zone - Erosion gt open fault conduit at seafloor
- Gas bubble migration paths (gas buoyancy and
capillary forces) - Canyon outlets into the deep basins appear as
favorable sites - Most active sites probably correspond to local
flow cells - basin scale(s), H 1 - 5 km, Z gt 50 m
- small scale, Z 3-10 m, H lt 200 m
- What could be the relationships with the
earthquake cycle ? - Gas expulsion and seawater intrusion (and
landslides Kuscu et al., 2005) as a consequence
of ground shaking. - Conduit permeability expected to decrease with
time due to authigenic carbonate formation. - Deeper source, variable in time and space, cannot
be excluded. - Local flow cells may respond to strain and stress
variations.
12Cold seep response to strain
OBS flow meter deployments
- Correlated fluid pulsing and seismic tremors in
the Costa Rica subduction zone (Brown et al.,
2005)
13Marnaut - Atalante cruise with manned submersible
Nautile - 2007
- Initial objectives (2004)
- Tectonic context of cold seeps
- Fluid sampling
- Biogeochemistry of authigenic carbonates
- Additional objectives
- Gas distribution in the sediment (deep-tow CHIRP
- availability issue) - Canyons and slope instability
- Hydrogeology flow-meters (SCRIPPS, M. Tryon),
piezometers (Ifremer) - Rare gasses (Helium isotopes)
- Initiate studies of temporal variability
- Strain - fluid flow coupling
- Flow meters, OBSs (4), Piezometers
- Time series of chemical and isotopic composition
(SCRIPPS (D. Hilton) - CRPG (B.Marty, S.
Bourlange)) - Osmotic pumps with copper tubes
- Extend the experiment from 1 month (cruise
duration) to 1 year. - Cruise proposal in January 2007 to use an Ifremer
ship for instrument recovery and additional work
(High resolution bathymetry, and sounding using
AUV or deep-tow). - Alternate solutions in Turkey for instrument
recovery.
14ESONET observatory sites (N. Cagatay)
15Scientific hypotheses to be tested with permanent
observatory
- Strike-slip motion is localized on a main crustal
shear zone, microseismically active, but locked. - Faults observed on the seafloor are locked and
accomodate slip only during earthquakes. - Sediment input to the deep basins is episodic
(earthquakes, floods, landslides). - Fluid expulsion varies in time and space
throughout the seismic cycle. - Formation of carbonate crusts and chimneys is
fast (100 yrs - what is the evolution since 1912
?). - Fluid expulsion at the seafloor has an impact on
the water column and may contribute to the
injection of methane into the atmosphère.