Aksu et al. (2000) present a geometric model for the Marmara Sea that features northeast-elongate fault-bounded ridges and basins bound by two east-west branches of the North Anatolian right-lateral transform. They state: (1) "The basins and ridges are rotating counterclockwise...," and (2) "...the entire negative flower structure is in a state of wholesale crustal extension." We are not in a position to evaluate the mapping, but if their fault geometry is correct, we suggest that it is consistent with the clockwise block rotation expected in a right-lateral transform (i.e., like books rotating on a shelf; McKenzie and Jackson, 1986; Lamb, 1994), not counterclockwise as stated in (1). Further, shortening (not extension) is expected across the northeast-striking faults in a right-lateral transform system for the given geometry (for anglef > 90°; inset to Fig. 1) unless east-west divergence between the rotating blocks is permitted; and extension is expected across the east-west faults. To demonstrate the expected zones of shortening (stippled areas in Fig. 1) and extension (overlap zones of Fig. 1) for the Aksu et al. (2000) geometry, we restore the blocks to their 1 Ma positions, assuming an Anatolia-Eurasia relative velocity as determined by Global Positioning System (GPS) data at GPS station ERDE (Fig. 1; McClusky et al., 2000). Seismic reflection profiles seem to support our dextral kinematic model as Okay et al. (2000) interpret young short-wavelength compressional folding along the southeast flank of the Central Marmara Ridge ( d in Fig. 1) and long-wavelength anticlines across a and d (Fig. 1). These structures resemble anticlines in California above (oblique) thrust-reactivated blind faults (Seeber and Sorlien, 2000). Shortening structures and thrust earthquakes are also associated with clockwise block rotation and termination of strike-slip faults within the pull-apart Salton Trough of California (Armbruster et al., 1998). Thus, the fault geometry proposed by Aksu et al. (2000) is consistent with shortening synchronous with extension within Marmara Sea if it is interpreted as a clockwise rotation system.
Aksu, A.E., Calon, T.J., Hiscott, R.N., and Yasar, D., 2000, Anatomy of the North Anatolian fault zone in the Marmara Sea, western Turkey: GSA Today, v. 10, no. 6, p. 3-7.
Armbruster, J.G., Seeber, L., Sorlien, C.C., and Steckler, M.S., 1998, Rotation vs. rifting in an extensional jog: Salton trough, California: EOS, (Transactions, American Geophysical Union), v. 79, p. F565.
Lamb, S.H., 1994, Behavior of the brittle crust in wide plate boundary zones: Journal of Geophysical Research, v. 99, p. 4457-4483.
McClusky, S., and 27 coauthors, 2000, Global Positioning System constraints on plate kinematics and dynamics in the eastern Mediterranean and Caucasus: Journal of Geophysical Research, v. 105, p. 5695-5719.
McKenzie, D.P., and Jackson, J.A., 1986, A block model of distributed deformation by faulting: Geological Society [London] Journal, v. 143, p. 349-353.
Okay, A.I., Kaslilar-Ozcan, A., Imren, C., Boztepe-Guney, A., Dermirbag, E., and Kuscu, I., 2000, Active faults and evolving strike-slip basins in the Marmara Sea, northwest Turkey: a multichannel seismic reflection study: Tectonophysics, v. 321, p. 189-218.
Seeber, L., and Sorlien, C.C., 2000, Listric thrusts in the western Transverse Ranges, California, Geological Society of America Bulletin, v. 112, p. 1067-1079.
Christopher C. Sorlien
See above listing.
Ali E. Aksu, email@example.com
Tom J. Calon
Richard N. Hiscott
Memorial University of Newfoundland
St. John's, Newfoundland A1B 3X5