Hydrologic and Geochemical Measurements During the MARNAUT Project,

Marmara Sea, Turkey

NSF Award No. OCE-0647361, April 1 2007 - March 31 2009

Introduction

We have been invited to join the joint French-Turkish funded MARNAUT Project including a one month cruise aboard the R/V Atalante with the Nautile submersible to the Marmara Sea, Turkey, in May-June of 2007 with an instrument recovery cruise a year later. The objective of the project (X. Le Pichon, N. Gorur, Principal Investigators, P. Henry, C. Sengor, Chief Scientists) is to study manifestations of fluid expulsion associated with the Main Marmara Fault (MMF), the submerged western extension of the North Anatolian Fault Zone (NAFZ). Our involvement in this project is focused on the theme of understanding the relationship between seismic activity and fluid migration/expulsion processes along this active plate boundary. To this end, we will provide both a temporal record of fluid flux rates of submarine seeps associated with faulting in specific regions of the basin, and a complementary long-term temporal record of fluid and gas chemistry of the seeps by deploying our CAT Meters for one year. The resulting time series of flow and seep chemistry will be related to seismic events and aseismic creep recorded by local seismic and GPS arrays. We envisage that this will ultimately become a long-term program of observation and monitoring of fluid activity in Marmara Sea. We and our MARNAUT collaborators will focus on the following issues:

  1. Studying the 3-D spatial relationship between fault structures and the presence and migration of fluids. Based on a detailed geophysical dataset of fault distribution acquired by the MARNAUT proponents during previous cruises, we will expand the seafloor mapping of fluid emission sites, including submersible visual observations and methane-plume mapping, and direct measurement of flow rate and pore pressure with the aim of mapping their spatial distribution in relation to the stress/strain distribution over the Marmara Sea. This will also include a geochemical investigation of the emitted fluids and dissolved gases aimed at recognizing the origins of the fluid sources.
  2. Studying the temporal relationship between seismic activity and fluid flow spanning historic through current activity. We will make time series measurements of seep flow rate and geochemical output to compare with both GPS records and land- and sea-based seismic records. We will look at the temporal record of He and C isotopes to constrain the source depth of fluids and to discern any change in the source region that may accompany seismic events. We will also investigate the flow and gas geochemistry of sites of past major earthquakes to help constrain the evolution of hydrotectonic response to these events. Other participants will investigate other biogeochemical processes in the sediment induced by the expulsion of methane-rich fluids, which can potentially provide information on the timing of past fluid emission activity.

A summary by Pierre Henry (CEREGE/College de France, CNRS, Aix-en-Provence)

and Naci Görür (ITU, Istanbul)

MARNAUT is a cruise of Ifremer/Genavir RV Atalante in the Sea of Marmara, with manned submersible Nautile. It is a multidisciplinary cruise with objectives centered on the relationships between active faults, fluid emissions, and landslides. Turkish partner institutions involved in MARNAUT are ITU (Istanbul Technical University) and MTA (Maden Tetkik ve Arama, Ankara). MARNAUT is also a step toward the development of permanent seafloor observatories on the North Anatolian Fault in the Sea of Marmara, within the European framework of the ESONET Network of Excellence. Turkish ESONET partners are ITU, KOERI (Kandili Observatory and Earthquake Research Institute, Bogaziçi University), and DEU (Dokuz Eylul University, Izmir).

The Sea of Marmara and Istanbul area is the only one along the North Anatolian Fault system that did not experience a large earthquake during the 20th century. It thus presents an exceptionally high earthquake risk. Following the Kocaeli (Izmit) and Düzce earthquakes in 1999, the Turkish-French Cooperation Program on the seismotectonics and the seismic risk in the Sea of Marmara and Istanbul area was launched. Cruises MARMARA (bathymetry and SAR-Pasisar), SEISMARMARA (multichannel seismics) and MARMARASCARPS (ROV Victor) showed the geometry of the fault system and found probable earthquake ruptures at the bottom of the Sea of Marmara. Based on these investigations, an earthquake of magnitude Mw = 7.2 or more is expected. Important remaining questions are: what is the extent and timing of past earthquakes ruptures in the Sea of Marmara? What is the geometry of the deep crustal faults? What is the possible role of co-seismic landslides as tsunami sources? The next stage of Turkish-French cooperation comprises the development of sea-floor observatories, which will complement the seismological network operated by KOERI on land. Observatory demonstration operations and scientist exchange will take place from 2007 to 2010 within the ESONET framework.

Investigations with towed camera (RV Meteor, cruise 44) and remotely operated vehicle (MARMARASCARPS cruise of RV Atalante), found fluid expulsion along the active fault scarps. While the water expelled at the vents was never sampled, sediment cores taken in the Sea of Marmara (e.g. cruise MARMARA VT/MARMACORE II of RV Marion-Dufresne) contain brackish water at more than 10 m depth below the seafloor. The peculiar history of the Sea of Marmara, which was a lake during glacial times, could explain this observation, as well as the unusual water expulsion activity observed along the seafloor trace of the Main Marmara Fault. We wonder how this activity varies throughout the earthquake cycle and aim to set a seafloor observatory combining seismology with measurements of strain, pore pressure and fluid fluxes.

The specific objectives of the MARNAUT cruise are:

  1. To perform an initial test of seafloor observatory concept, developed within the framework of ESONET Network of Excellence, and provide the initial conditions.
  2. To assess the influence of the earthquake cycle on fluid movements in the sediment, and also investigate other factors (climate change and paleoceanography)
  3. To measure fluid fluxes along the fault zone and determine the relationship between fluid emissions at the seafloor and deep processes in the seismogenic zone (zone of earthquake slip at depth) and mantle.
  4. To identity landslides and zones of instability, assess their recent activity and measure current pore fluid pressure conditions within or above the landslides.
  5. To recognize in the sedimentary record recent earthquake and tsunami events (particularly in Çinarçik basin) and correlate them with the historical record.
  6. To study biogeochemical processes at seafloor vent sites, and evaluate their influence on environmental conditions in the Sea of Marmara.

One practical question asked is whether the deployment of a permanent observatory on seafloor vent sites in the Sea of Marmara is relevant for the study of fluid-deformation coupling in fault zones. Long term (4 months to 1 year) monitoring experiments performed at the occasion of MARNAUT cruise in 2007 and of the MARMESONET cruise, projected in 2008, will gather data to answer this question. Better understanding of fluid-fault coupling processes may, hypothetically, lead to the recognition of earthquake precursors and also improve assessment of slope instability. However, the outcome of this approach for earthquake and tsunami risk assessment should be considered in the very long term.

The MARNAUT Project is an international collaborative project including researchers from France (Ifremer, CNRS, INSU, IUT), Turkey (ITU, MTA), Italy (ISMAR), Germany (GEOMAR, Berlin Free Univ.), and USA (Scripps Inst.).

More information is available at Pierre Henry's MARNAUT website:

http://www.cdf.u-3mrs.fr/%7Ehenry/marmara/index.html