Publication Date:
2005
Description:
Earthquake scarps associated with recent historical events have been found
on the floor of the Sea of Marmara, along the North Anatolian Fault (NAF). The
MAuto-Regressive Moving Average-processRASCARPS cruise using an unmanned submersible
(ROV) provides direct observations to study the fine-scale morphology and geology of
those scarps, their distribution, and geometry. The observations are consistent with the
diversity of fault mechanisms and the fault segmentation within the north Marmara
extensional step-over, between the strike-slip Ganos and Izmit faults. Smaller
strike-slip segments and pull-apart basins alternate within the main step-over, commonly
combining strike-slip and extension. Rapid sedimentation rates of 1-3 mm/yr appear to
compete with normal faulting components of up to 6 mm/yr at the pull-apart margins. In
spite of the fast sedimentation rates the submarine scarps are preserved and accumulate
relief. Sets of youthful earthquake scarps extend offshore from the Ganos and Izmit
faults on land into the Sea of Marmara. Our observations suggest that they correspond to
the submarine ruptures of the 1999 Izmit (Mw 7.4) and the 1912 Ganos (Ms 7.4)
earthquakes. While the 1999 rupture ends at the immediate eastern entrance of the
extensional Cinarcik Basin, the 1912 rupture appears to have crossed the Ganos
restraining bend into the Sea of Marmara floor for 60 km with a right-lateral slip of 5
m, ending in the Central Basin step-over. From the Gulf of Saros to Marmara the total
1912 rupture length is probably about 140 km, not 50 km as previously thought. The
direct observations of submarine scarps in Marmara are critical to defining barriers
that have arrested past earthquakes as well as defining a possible segmentation of the
contemporary state of loading. Incorporating the submarine scarp evidence modifies
substantially our understanding of the current state of loading along the NAF next to
Istanbul. Coulomb stress modeling shows a zone of maximum loading with at least 4-5 m of
slip deficit encompassing the strike-slip segment 70 km long between the Cinarcik and
Central Basins. That segment alone would be capable of generating a large-magnitude
earthquake (Mw 7.2). Other segments in Marmara appear less loaded. FROTH
Keywords:
Earthquake hazard
;
Turkey
;
Fault zone
;
NAF
;
G3
;
G-cubed
;
AGU
;
Ucarkus
;
Lepinay
;
Cagatay
;
Cakir
;
Structural geology
;
7230
;
Seismology:
;
Seismicity
;
and
;
tectonics
;
Oezalaybey
;
Ozalaybey
;
Lefevre
;
7223
;
Earthquake
;
interaction,
;
forecasting,
;
and
;
prediction
;
morphology
;
submersible
;
8110
;
Tectonophysics:
;
Continental
;
tectonics:
;
general
;
1766
;
1894
;
1912
;
1999
;
Earthquake
Permalink
