Holocene ruptures along the North Anatolia Fault in the Marmara Sea, Turkey: Sedimentary processes, spatial extent and age
Abstract
The North Anatolian fault (NAF), which extends east west for over 1600 km across Turkey, is one of the world's major continental transforms. Since 1939, a sequence of M>7 earthquakes ruptured progressively westward the entire NAF east of Marmara. The most recent and westernmost events in this sequence, the Mw7.4 Izmit and the Mw7.2 Duzce main shocks of 1999, ruptured about 160 km of the fault and were particularly destructive (~17,000 deaths). The only portion of the NAF that did not rupture in the last century is the segment beneath the Marmara Sea that is considered a seismic gap and presents high risk to Istanbul and surroundings. To decipher Holocene earthquake ruptures and the processes leading to their signature in the sedimentary record we applied submarine paleoseismology techniques to study a transect of three 10 m long cores recovered from the Central Basin. The sediments were analyzed with x-ray radiography, for grain size variability at cm-scale, geochemical elements at mm-scale and physical properties. These measurements were calibrated to a chronology developed from short-lived radioisotopes (137-Cs, 210-Pb) and radiocarbon. Turbidites were sampled from the deepest part of the Central Basin, from 1248 to 1262 m depth. As previously documented by McHugh et al (2006), these turbidites are characterized by multiple sand and coarse silt beds, each normally graded, and that together grade upwards into a non-stratified silt that also fines upwards. Elemental concentrations of Al and Si increase with the sand and coarser silt components indicative of an influx of terrigenous components. These complex turbidites-homogenites are as thick as 1 m and dominate the sedimentation in the basin (≈80%). The remainder includes 10 to 20 cm thick fining upwards silt deposits. We interpret these depositional events to represent large earthquakes, the ones including transport of sand are proximal, and the ones without the sand are distal. We measured concentrations of Ca within the coarse component of the complex turbidite and depletion of Mn above. These elemental trends, previously documented by Cagatay et al (2008) can generally be associated with the turbidite-homogenite units and are linked to diagnetic processes resulting from diffuse fluid/gas escape during strong shaking of the sea floor or after the earthquake. Fifteen turbidites-homogenites were preserved within the past 4000 years with an average recurrence interval of 300 years. This is consistent with previous estimates and with a constant slip rate for the NAF for the mid to late Holocene. We have tentatively linked one of the turbidite-homogenite deposits to the 740 AD historical earthquake and two others to possibly the 1912 > Ms 7.4 and more distal 1963 or 1964 events Ms >6.4 linked to the Yalova and Manyas faults, respectively.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.T33B2235B
- Keywords:
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- 3022 MARINE GEOLOGY AND GEOPHYSICS / Marine sediments: processes and transport;
- 3025 MARINE GEOLOGY AND GEOPHYSICS / Marine seismics;
- 8123 TECTONOPHYSICS / Dynamics: seismotectonics