Research on Ocean Margin Earthquakes: A study to assess physico-chemical behaviour during geotechnical experiments simulating upper seismogenic zone conditions: The Gibraltar, Nankai, and Costa Rican subduction zones

• Applicant: Professor Dr. Achim Kopf
• Subject Area: Palaeontology
• Term: from 2005 to 2010
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5450228

• Final Report Year: 2010

Final Report Abstract

The project ROME combined (i) the technological development of hydrothermal oedometer systems which cover the stress and temperature range around the up-dip limit of the seismogenic zone, and (ii) experiments concerning the geochemical, mechanical, and hydrological response (fluid-rock interaction, pore pressure, shear strength, permeability) of marine, seawater-saturated sediments. The working hypothesis to test was whether there are preferably weak mineral phases (such as clays) or authigenic cements from temperature-driven mineral transformation in the fault zone. Both processes could effectively cause fault seal and the formation of excess pore pressure transients. The main aims were (i) to separate the two processes is a combined approach of shear and compaction tests at variable temperatures, the latter additionally monitoring changes in geochemistry in the sediment and pore fluid continuously, and (ii) to explore the role of geochemical, mineralogical, and structural phenomena governing the overall strength of the samples. First, the main components of the two heatable uniaxial systems were purchased. The two deformation systems got assembled and were tested successfully with clay mineral and quartz standards. In parallel, ring shear tests were carried out on samples two of the three study areas: (1) the Costa Rica margin (cruises M54 with RV Meteor, Ticoflux, and ODP Leg 170), and (2) the Nankai Trough (DSDP Leg 31). Some of the Nankai ring shear tests were also carried out heated (20, 50 and 80°C). Following that, uniaxial tests were carried out at 20, 100 and 150°C on Nankai samples. Results show prominent thermal consolidation effects that allow us to reinterpret earlier pore pressure estimates for this subduction system. In addition, ring shear testing was continued and some of the thermally altered oedometer specimens were sheared remoulded under room temperature and heated conditions. Direct shear tests were also carried out on these samples, however, the low effective normal stresses of the RCOM direct shear apparatur makes a direct comparison to the high stress data difficult. While semiquantitative XRD work attests illitisation of smectite during our tests, only very preliminary geochemical data on solid and fluid phases from the deformation experiments could be completed during the course of the initial part of the project. Meanwhile, hydrothermal testing commenced on various mineral standards at elevated temperatures as well as natural samples of marine sediments.

Publications

• 2006. Geotechnical and geochemical investigations of the Marquês de Pombal landslide at the Portuguese continental margin. Norwegian Journal of Geology 86/3: 187-198
  Minning, M., Hebbeln, D., Hensen, C., Kopf, A.
  
• EGU meeting 2007, Vienna: Consolidation experiments of marine sediments under hydrothermal conditions; implications for waterrock interaction in the shallow subduction zone
  A. Hüpers, A. Kopf
  
• GV meeting 2007, Bremen: Alteration of underthrust deep sea sediments - first results from high pressure compaction tests at elevated temperatures
  A. Hüpers, A. Kopf
  
• DFG-IODP Kolloquium 2008, Hannover: On the role of temperature on the stress state of underthrust sediments at the Nankai margin
  A. Hüpers, A. Kopf
  
• DFG-IODP Kolloquium 2008, Hannover: Physical properties of marine sediments undergoing subduction: Results from heated shear experiments at the Nankai convergent margin
  Zimmermann, K., Hüpers, A., Kopf, A.
  
• EGU 2008, Vienna: New insights into the stress state of underthrust sediments at the Nankai margin
  A. Hüpers, A. Kopf
  
• Jahrestagung Geol. Vereinigung 2009, Aachen (Sept. 2008): The influence of temperature on excess pore pressure estimates in underthrust sediments at the Nankai margin
  A. Hüpers, A. Kopf
  
• 2009. The thermal influence on the consolidation state of underthrust sediments from the Nankai margin and its implications for excess pore pressure. Earth & Planetary Science Letters, 286: 324-332
  Hüpers, A., Kopf, A.
  
• IODP-ICDP Colloquium, 16.-18. March 2009, Potsdam: Ramifications of high insitu temperatures for geotechnical testing at ambient temperature conditions - a case study from the Nankai margin
  A. Hüpers, S. Kreiter, A. Kopf
  
• EGU Vienna, May 2010: Hydrothermal water-rock interaction of underthrust sediments with seawater - an experimental approach
  A. Hüpers, A. Kopf
  
• IODP-ICDP Colloquium, 9.-11. March 2010, Frankfurt: Compaction tests of deep sea sediments at elevated temperatures: implications for physical properties and pore water geochemistry of subducting sediments
  A. Hüpers, A. Kopf