Slip History of the 1944 Rupture Segment on North Anatolia Fault Near Gerede, Turkey: Constraints on Earthquake Recurrence Models
Abstract
Completeness of historic earthquake catalogs must be examined by geologic records, though the geologic records are not always more complete and precise than historic records. The historic records on large earthquakes from the North Anatolian fault are tested in trenches on the 1944 segment. Previous results indicated 3 historic and 1 geologic events in past 1000 years with characteristic ~ 5 m slip and quasi-periodic recurrence every 200-280 years. The one geologic event without historic information is critical to know the recurrence behavior of the fault and catalog evaluation. We excavated seven new trenches at the Ardicli paleoseismic site, located about 15 km east of Gerede, to resolve displacement on a Byzantine-aged channel and the timing of the offsets. The channel appears to have been excavated to drain the site and allow mining of clay for making bricks and tiles: a kiln was found adjacent to the channel. The V-shaped channel thalweg is offset 13.5+1.5 m, and based on many cross-fault trenches, represents slip in the past three surface ruptures. Dating of the channel is on pine cones, wood and charcoal that are incorporated into the channel deposits and in the stratified sediments into which the channel is cut: current dating suggests that this channel dates to the 9th-11th century AD. If confirmed with additional dates, the surface rupture that initially offset the channel likely corresponds to the historically-reported earthquake in AD 1035. The surface geomorphology records displacement from two more recent events. The 1944 surface rupture in this region produced 4-5 m of slip based on offset field boundaries and small channels. Older fluvial channels and rills in this area show about 10 m of displacement. We dated the fill from a 10 m offset channel, and place the penultimate event as younger than about AD 1650, which must correspond to the well-documented earthquake in 1668. From our previously reported work, we resolved 22-26 m of displacement for the past five surface ruptures on a 6th century channel. Together, these data argue for fairly characteristic slip for the past five earthquakes. However, the timing between events ranges from less than two centuries to more than six centuries, and there is no apparent correspondence between the lapse time and the amount of ensuing displacement. These observations argue against both the time- and slip-predictable models of earthquake recurrence.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.S41A1897O
- Keywords:
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- 7221 SEISMOLOGY / Paleoseismology;
- 7250 SEISMOLOGY / Transform faults;
- 8111 TECTONOPHYSICS / Continental tectonics: strike-slip and transform;
- 8158 TECTONOPHYSICS / Plate motions: present and recent