a deep Geophysical Observatory at the North Anatolian Fault
An international workshop discussing the project GONAF: A deep Geophysical Observatory at the North Anatolian Fault
, was held 23-27 April 2007 in Istanbul/Turkey (Dresen et al., 2008). The aim of this workshop was to discuss and strengthen plans for the here proposed deep drilling project. The workshop was sponsored by ICDP and the important outcomes have been incorporated in the present proposal.
Presentations at the workshop included an extensive overview of existing fault drilling projects, a session on seismotectonics, seismology and the geological setting of the western part of the NAFZ and the Sea of Marmara region and a series of contributions on deep borehole monitoring results and technical efforts. Reports on on-going and recently completed fault drilling projects provided insight in exciting scientific results such as fault mechanics and earthquake processes as well as technical and logistical challenges of a drilling program. The reports presented at the workshop included projects in California (SAFOD; Zoback, Hickman, Ellsworth), Taiwan (TCDP; Ma, Tanaka), Japan (Nojima Fault; Ito) and Greece (CRL; Cornet). All fault drilling projects produced new and ground-breaking results with regard to physics of faulting, slip distribution at hypocentral depth, source mechanisms and the earthquake energy budget. A series of presentations provided a detailed overview of structure, kinematics and seismotectonics of the western NAFZ emphasizing recent and partly unpublished field data. Controversial views of fault structure and hypocenter locations in the Sea of Marmara accentuated the need for high-resolution long-term seismological observations achieved through building up a deep geophysical observatory at the NAFZ and in vicinity to the mega-city Istanbul. In particular, detailed introductions presented new scientific results and technical developments covering high-resolution earthquake monitoring, strain monitoring, velocity measurements, stress measurements, heat and fluid flow measurements and borehole logging techniques.
The potential GONAF drill site on the island of Sivriada was visited during a one-day field trip and a brief summary with a list of suggested pre-site and drilling-phase studies concluded the workshop. Key aspects of a potential scientific and technical program for a deep drill hole and a long-term deep geophysical observatory were discussed that were further developed in the meantime forming the base for the here presented full proposal. As a result of the workshop consensus was reached that the suggested drill site is unique in that it represents the only possible location for installation of a deep borehole observatory at the seismic gap of the NAFZ just south of Istanbul.
Dresen, G., Bohnhoff, M., Aktar, M., Eyidogan, H., (2008), Drilling the North Anatolian Fault. - Scientific Drilling, 6, 58-59 DOI: 10.2204/iodp.sd.6.10.2008
Bulut, F., Bohnhoff M., Ellsworth W. L., Aktar M. and Dresen G., (2009), Microseismicity at the North Anatolian Fault in the Sea of Marmara Offshore Istanbul, Journal of Geophys. Res., doi: 10.1029/2008JB006244