Submarine fault scarps in the Sea of Marmara pull-apart ... - HAL - IRD

Geochemistry
Geophysics
Geosystems G 3
G 3 armijo et al.: sea of marmara pull-apart 10.1029/2004GC000896
Figure 6. Submarine scarps in the Central Basin compared with similar scarps on land near Eften lake extensional
step-over. (a) Side-scan sonar image (illuminated from the SE) of large en echelon scarps with normal and rightlateral
strike-slip components on the SW boundary fault of the inner Central Basin pull-apart (compare with Figures 4
and 5). (b) Scarps with similar features but substantially smaller near the western termination of the 12 November
1999 Duzce earthquake rupture (Mw 7.2). Individual scarps with free faces 20–50 cm high associated with the Duzce
earthquake lacerate obliquely a cumulative normal fault scarp 4 m high. The inlet providing water to the pool has
been right-laterally offset 1.5 m across individual fault scarp at the very base of the cumulative scarp. Total normal
and strike offsets reached 4 m in 1999 in the Eften area [Akyüz et al., 2002].
along strike, attesting that there is no systematic
vertical offset of the morphology; thus the prevailing
motion across the fault is strike-slip.
[26] The most outstanding feature is the continuity
and the linearity of a set of scarps that are in many
places less than 0.5 m high (less than one contour
line in the microbathymetry map; Figure 7). This
set of continuous individual scarps comes into
sight in the microbathymetry as a sharp cut made
into the soft sediments covering the smooth topography
of the Western High. Visual inspection with
the ROV proved that the small-scale scarps are
mantled with a drape of soft pelagic sediments and
Figure 7. Morphology of EW-striking, purely strike-slip fault scarps across the Western High. (a) Microbathymetry
(top) and corresponding side-scan sonar image (bottom) show smooth sea-bottom morphology disrupted by a sharp,
continuous break along the linear fault trace (outlined by red arrows). Disruption of morphology occurs at various
scales with opposite north- and south-facing vertical offsets suggesting prevailing strike-slip. Pressure ridges and
pull-apart ponds can be seen (examples identified). Contours each 0.5 m. (b) Enlargement of shallowest area (box in
Figure 7a), where sea-bottom landforms are clearly offset laterally. (c) Restoring offsets of individual scarp requires
6 ± 1 m of right-lateral slip, which could result mostly from rupture of a large earthquake.
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