Paleoseismology of the Gazikoy-Saros segment of the North Anatolia fault, northwestern Turkey: Comparison of the historical and paleoseismic records, implications of regional seismic hazard, and models of earthquake recurrence (original) (raw)
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Bulletin of the Seismological Society of America, 2003
Paleoseismologic data from trenches excavated across the central part of the North Anatolian fault at Alayurt, Turkey, reveal evidence for at least four, and possibly five, surface ruptures during the past 2000 years, as well as one much older event. These surface ruptures, as recognized on the basis of upward fault terminations and colluvial gravel layers, include (1) the historic 1943 M w 7.7 Tosya earthquake;
Bulletin of the Seismological Society of America, 2009
The North Anatolian Fault (NAF) is a ~1500-km-long, arcuate, dextral strike-slip fault zone in northern Turkey that extends from the Karliova triple junction to the Aegean Sea. East of Bolu, the fault zone exhibits evidence of a sequence of large (Mw>7) earthquakes that occurred during the 20 th century that displayed a migrating earthquake sequence from east to west. Prolonged human occupation in this region provides an extensive, but not exhaustive, historical record of large earthquakes prior to the 20 th century that covers much of the last 2000 years. In this study, we extend our knowledge of rupture events in the region by evaluating the stratigraphy and chronology of sediments exposed in a paleoseismic trench across a splay of the NAF at Destek, ~6.5 km east of Lake Ladik (40.868°N, 36.121°E). The trenched fault strand forms an uphill-facing scarp and associated sediment trap below a small catchment. The trench exposed a narrow fault zone that has juxtaposed a sequence of weakly-defined paleosols interbedded with colluvium against highly-fractured bedrock. We mapped magnetic susceptibility variations on the trench walls and found evidence for multiple visually unrecognized colluvial wedges. This technique was also used to constrain a predominantly dip-slip style of displacement on this fault splay. Sediments exposed in the trench were dated using both charcoal and terrestrial gastropod shells to constrain the timing of the earthquake events. While the gastropod shells consistently yielded 14 Cages that were too old (by ~900 years), we obtained highly reliable 14 Cages from the charcoal by dating multiple components of the sample material. Our radiocarbon chronology constrains the timing of seven large earthquakes over the past 3000 years prior to the 1943 Ladik earthquake, including-1788AD, 1034-1321AD, 549-719AD, 17-585AD (1-3 events), 351BC-28AD, 700-392BC, 912-596BC. Our results indicate an average inter-event time of 385±166yrs
Geological Society, …, 2009
We conducted palaeoseismic studies along the North Anatolian fault both east and west of the Marmara Sea to evaluate its recent surface rupture history in relation to the well-documented historical record of earthquakes in the region, and to assess the hazard of this major fault to the city of Istanbul, one of the largest cities in the Middle East. Across the 1912 rupture of the Ganos strand of the North Anatolian fault west of the Marmara Sea, we excavated 26 trenches to resolve slip and constrain the earthquake history on a channel-fan complex that crosses the fault at a high angle. A distinctive, well-sorted fine sand channel that served as a marker unit was exposed in 21 trenches totaling over 300 m in length. Isopach mapping shows that the sand is channelized north of the fault, and flowed as an overflow fan complex across a broad fault scarp to the south. Realignment of the feeder channel thalweg to the fan apex required about 9+1 m of reconstruction. Study of the rupture history in several exposures demonstrates that this displacement occurred as two large events. Analysis of radiocarbon dates places the age of the sand channel as post AD 1655, so we attribute the two surface ruptures to the large regional earthquakes of 1766 and 1912. If each was similar in size, then about 4 -5 m of slip can be attributed to each event, consistent with that reported for 1912 farther east. We also found evidence for two additional surface ruptures after about AD 900, which probably correspond to the large regional earthquakes of 1063 and 1344 (or 1354). These observations suggest fairly periodic occurrence of large earthquakes (RI ¼ c. 283+113 years) for the past millennium, and a rate of c. 16 mm/a if all events experienced similar slip.
2010
The North Anatolian Fault Zone is one of the Earth's most important active dextral strike-slip structures, which is extending more than 1500 km from the eastern Turkey to the northern Aegean Sea. This deformation zone is the northern boundary of the westward moving Anatolian block and connects Aegean extensional regime with East Anatolian high plateau. 26 December 1939 Erzincan (Ms=7.8) and 20 December 1942 Erbaa-Niksar (Ms=7.1) earthquakes created a total surface rupture more than 400 km between Erzincan and Erbaa on the middle to eastern sections of the North Anatolian Fault. These two faulting events are separated by a 10-km-wide releasing step-over, acted like a seismic barrier in the 20th century. In contrast, the historical Anatolian Earthquake of 17 August 1668 is thought to have a probable rupture length of more than 400 km, starts from east of Gerede, crossing the 10-km-wide releasing step-over at Niksar, and stops somewhere close to Koyulhisar. However, some other historical earthquake catalogues do not share the idea of a single very large earthquake and mention a series of events between July and September 1668 at various places. In the framework of T.C. D.P.T. Project to 2006K.120220 we undertook paleoseismological trench investigations on the Kelkit Valley segment to test the multi-cycle earthquake behavior of the North Anatolian Fault at this structural complex section. We found evidences for three surface faulting earthquakes predating the 1939 event during the past millennium in trenches, excavated at Reşadiye (40.38N, 37.35E) and Umurca (40.33N, 37.35E). While Reşadiye trench is excavated on alluvial fan deposits at the east of the Reşadiye town, where sedimentation is modified by a man-made artificial channel after a certain period of time, Umurca trench is located at the distal part of an alluvial fan at 23 km east of Reşadiye trench. In addition to the 1939 Erzincan earthquake, prior earthquake surface ruptures are interpreted as: (a) 17 August 1668, (b) A.D. 1254, and (c) A.D. 1045 events. The 17 August 1668 Anatolia earthquake surface rupture is reported in previous paleoseismological studies on different segments of the North Anatolian Fault, which have created individual earthquakes at 1942, 1943, and 1944 in the 20th century. Taking into account previous studies and our results, we suggest very large 17 August 1668 historical strike-slip earthquake surface rupture jumped the 10-km-wide releasing step-over at Niksar and continued towards east until somewhere close to Koyulhisar. The existence of different magnitude offsets of field boundaries (sets of 4 m, 6.5 m, and 10.8 m) shows the effect of multiple events, in which 1939, 1668, and 1254 surface ruptures have around 4, 2.5, and 4 meters of coseismic horizontal slip on the Kelkit Valley segment, respectively.
Earth and Planetary Science Letters
The East Anatolian Fault (EAF) in Turkey is a major active left-lateral strike-slip fault that was seismically active during the 19th century but mostly quiet during the 20th century. Geodetic data suggests that the fault is creeping along its central part. Here we focus on its seismic history as recorded in the sediments of Lake Hazar in the central part of the EAF. Sediment cores were studied using X-ray imagery, magnetic susceptibility, grain-size, loss-on-ignition and X-ray fluorescence measurements. Recurring thin, coarsegrained sediment units identified as turbidites in all cores were deposited synchronously at two deep study sites. The turbidite ages are inferred combining radiocarbon and radionuclide (137 Cs and 210 Pb) dating in an Oxcal model. A mean recurrence interval of ∼190 yrs is obtained over 3800 yrs. Ages of the recent turbidites correspond to historical earthquakes reported to have occurred along the EAF Zone or to paleoruptures documented in trenches just northeast of Lake Hazar. The turbidites are inferred to be earthquake-triggered. Our record demonstrates that Lake Hazar has been repeatedly subjected to significant seismic shaking over the past 3800 yrs. The seismic sources are variable: ∼65% of all turbidites are associated with an EAF source. The seismic cycle of central EAF is thus only partly impacted by creep.
Annals of geophysics = Annali di geofisica
The North Anatolian Fault is a ca. 1200-km-long, right-lateral, strike-slip fault that forms the northern boundary of the Anatolian plate. A damaging sequence of earthquakes ruptured almost the entire fault in the twentieth century. This study adds to the growing number of paleoseismic investigations of the 350-km-long 1939 Erzincan earthquake-rupture segment, which is towards the eastern end of the North Anatolian Fault in Turkey. Using three paleoseismic trenches located along ca. 2 km of the principal fault strand, this study determines the timing of five earthquakes prior to the 1939 earthquake. The first three of these earthquakes are correlated to historical earthquakes in A.D. 1668, 1254 and 499, and two further events were identified as occurring from 881-673 B.C. and from 1406-1291 B.C. (2v age ranges). By comparing the earthquake timing determined in this study to results from other paleoseismic investigations of the 1939 rupture segment, it becomes clear that this histori...
Paleoseismology of the western Sürgü–Misis fault system: East Anatolian Fault, Turkey
Mediterranean Geoscience Reviews
The East Anatolian fault bifurcates into a north strand and a south strand near the City of Çelikhan, Turkey. The northern strand is referred to as the Sürgü-Misis fault (SMF) system, which is divided into a number of distinct fault segments based on geological and geomorphological characteristics. However, no paleoseismological data regarding the movement history of the SMF system previously have been reported. We excavated seven trenches across four segments of the SMF system to evaluate the paleoseismological history of these fault zones. These trenches exposed structural and sedimentological evidence of paleoseismic events that had primarily strike-slip displacements with secondary normal and reverse components of motion. Geochronological dating of the trench stratigraphy and event horizons provide the time elapsed since the last event and confirmed the Holocene activity of the faults. These fault segments are individually capable of producing surfacerupturing earthquakes, but may also rupture together generating large, complex, multi-segment ruptures. However, the SMF system has not produced surface-rupturing earthquakes in the last millennia, and therefore is accumulating strain. In light of our findings, we suggest that about 1.7 m of strain has accumulated across the Karataş and Yumurtalık fault segments, which is sufficient to produce moderate to large earthquakes when released seismically. The surrounding Gulf of İskenderun is a highly industrialized district in the Eastern Mediterranean. Therefore, the data obtained from this paleoseismological investigation will contribute to a better understanding of the earthquake hazards in the region.
2011
Th e 26 December 1939 Erzincan (M s = 7.8) and 20 December 1942 Erbaa-Niksar (M s = 7.1) earthquakes created a total surface rupture more than 400 km between Erzincan and Erbaa on the middle to eastern sections of the North Anatolian Fault. Th ese two faulting events are separated by a 10-km-wide releasing stepover, which acted like a seismic barrier in the 20 th century. To understand the rupture behaviour in this structurally complex section of the North Anatolian Fault, we undertook palaeoseismological trench investigations on the Kelkit Valley segment where there is little or no palaeoseismic information. We found evidence for three surface faulting earthquakes predating the 1939 event during the past millennium in trenches excavated in Reşadiye and Umurca.