H. Serdar Akyüz

A 2500-yr-long paleoseismologic record of large, infrequent earthquakes on the North Anatolian fault at Çukurçimen, Turkey

Paleoseismologic trenches excavated across the North Anatolian fault near the village of Cukurcimen in north-central Turkey yield a complete record of surface ruptures for the past 2500 yr. The trenches provide mutually consistent evidence for the timing of the five most recent surface ruptures at the site, as well as at least two older events. These are interpreted as: (1) the historic 1939 M w 7.9 earthquake; (2) the historic 1254 A.D. earthquake; (3) the historic 1045 A.D. earthquake; (4) an earthquake that probably occurred late in the interval between 250 and 540 A.D., possibly the historic 499 A.D. earthquake; and (5) an earthquake that occurred sometime between 770 and 50 B.C. (and probably between 230 and 50 B.C.). One additional earthquake occurred sometime between 1450 and 800 B.C., and at least one other surface rupture occurred between 2880 and 200 B.C., but the stratigraphic section at the site was not completely exposed for sediments older than -2500 yr. As a result, it is unclear whether the oldest event horizons represent a single earthquake, or multiple events. Our findings, when coupled with other published results and the historical record, enable us to construct a space-time history of earthquakes along the North Anatolian fault. The most striking aspects of this analysis are: (1) the rarity of earthquakes at any given place along the fault, suggesting that the fault typically ruptures in large, infrequent events; (2) earthquake occurrence is relatively temporally regular, with inter-event times that range from -200 to <900 yr, and vary by a factor of only 3-4; and (3) almost the entire length of the North Anatolian fault ruptured in short-lived clusters of activity in the seventeenth to eighteenth centuries and in the tenth to twelfth centuries, similar to the twentieth-century sequence. The magnitude and sequence of the individual ruptures, however, have varied considerably between clusters. Moreover, the paleoseismologic and historical data indicate that the North Anatolian fault does not always rupture in sequences similar to the twentieth-century cluster. These results suggest that the relatively regular recurrence of rare, large-magnitude earthquakes may be the expected mode of earthquake occurrence on mature strike-slip faults in settings where such faults are structurally isolated from other major seismic sources.

Surface Rupture and Slip Distribution along the Karadere Segment of the 17 August 1999 İzmit and the Western Section of the 12 November 1999 Düzce, Turkey, Earthquakes

On 17 August 1999 the Mw 7.5 I zmit, Turkey, earthquake produced surface rupture in excess of 120 km, and perhaps as much as 200 km, with up to 5 m of dextral slip, along a western portion of the North Anatolian fault zone. The 12 November 1999 Mw 7.1 Duzce, Turkey, earthquake produced a 40-km-long sur- face rupture, including 9 km of rupture overlap with the eastern end of the August event. Our mapping focused on the 40-km-long Karadere rupture segment, the east- ernmost segment of the August event, as well as on the western 20 km of the No- vember rupture. Maximum dextral slip along the Karadere segment is approximately 1.5 m, and the average slip on this segment is close to 1 m. Although slip along the Karadere segment is considerably less than that on segments to the west, this segment is of particular interest for three reasons: (1) the western boundary of the Karadere segment is defined by the most striking structural discontinuity along the entire Au- gust surface rupture (i.e., a 5-km-wide zone of no surface rupture, as well as a 25 change in trend from E-W to ENE), and such a discontinuity may have important implications for rupture dynamics; (2) surface rupture terminates at the east end of the Karadere rupture segment at a 1.5- to 3-km-wide extensional step-over at Eften Lake; and (3) the 12 November 1999 Duzce earthquake reruptured the easternmost 9 km of the Karadere segment, raising interesting questions about rupture dynamics and interactions between events on adjacent fault segments. The details of the 17 August 1999 and l2 November 1999 surface rupture traces suggest that rupture may have partially propagated across the Eften Lake extensional step-over, although this step-over seems to have acted as an effective barrier to rupture propagation.

Basinward migration of rift-border faults: Implications for facies distributions and preservation potential

Basinward migration of half-graben footwall margins occurs throughout the active Aegean extensional province and has significant implications for facies distributions and preservation potential in synrift fills worldwide. Recognition of this phenomenon is particularly important for predicting the preservation and distribution of hydrocarbon reservoirs in rift basins. Using an example from the Gediz graben of western Turkey, it is shown that basinward migration of footwall margins exhumes proximal facies of lateral sedimentary systems, severely limiting their preservation potential and providing a ready source of easily erodible material. This in turn leads to the generation of extensive footwall-derived depositional systems, which frequently displace axial drainage systems toward the hanging-wall dip slope.

A 2000-Year-Long Paleoseismologic Record of Earthquakes along the Central North Anatolian Fault, from Trenches at Alayurt, Turkey

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; (2) an older event that is not well dated, but which we interpret as the great 1668 earthquake, which historical accounts suggest ruptured this part of the fault; (3) a late-eighth- to early-thirteenth-century surface rupture; (4) a surface rupture that occurred between the first and third centuries A.D., possibly the historic A.D. 236 event; (5) a possible surface rupture that occurred between the late fourth and early eleventh centuries A.D.; and (6) a much older event that occurred sometime between 4600 and 3550 B.C. Our documentation of a late-eighth- to early-thirteenth-century surface rupture at Alayurt is particularly important because, when taken in context with available historical and paleoseismologic data, it suggests the occurrence of a brief interval during which large earthquakes ruptured most of the North Anatolian fault. This interval resembles two other short-lived clusters of activity in the sixteenth to eighteenth and twentieth centuries. These brief intervals of activity are separated by much longer periods of relative quiescence that range from 250 years to ≤800 years (if there was not a late-fourth- to early-eleventh-century event) or ∼600 years (if there was a late-fourth- to early-eleventh-century event). The factor of 2–3 variation in inter-event times suggests quasiperiodic earthquake occurrence, which we attribute to the structural simplicity and relative isolation of the central North Anatolian fault from other earthquake-producing faults.

Geological and archaeological evidence for post– Roman earthquake surface faulting at Cibyra, SW Turkey

Abstract The NE–SW-trending Burdur–Fethiye fault zone is one of the major active fault zones of southwestern Turkey and the ancient city of Cibyra is located on this zone. Segments of the Burdur–Fethiye fault zone have ruptured in the historical period and during the 20th century. A detailed investigation in the ancient city of Cibyra showed the presence of faults sinistrally offset sitting rows of the stadium up to 50 cm. In addition, there are broken corners of blocks, collapsed walls, broken columns, and tilted and toppled blocks in existing major buildings in the city centre. Field observations showed that fractures and associated damage at Cibyra were produced by a post-Roman earthquake, possibly during the 417-A.D.-earthquake which had an intensity of 9 on the MSK scale.

Spatial slip behavior of large strike‐slip fault belts: Implications for the Holocene slip rates of the eastern termination of the North Anatolian Fault, Turkey

We present new data on Holocene slip rates for the eastern end of the North Anatolian Fault (NAF) by using the optically stimulated luminescence ages of the offset terrace deposits at two sites, where a total of four displaced landforms was studied. Each offset feature was analyzed independently, and three different assumptions were made for all the offsets, depending on whether the age of the upper tread (upper tread reconstruction), the lower tread (lower tread reconstruction), or all bounding surfaces (intermediate solution) were used in dating of the terrace risers. The deflected geometry of the risers strongly suggests the use of either the intermediate solution or the upper tread reconstruction. The joint slip rate distributions for the upper tread reconstructions and the intermediate solutions were modeled as 13.0 + 1.8 / −1.4 and 14.3 + 5.8 / −2.4 mm/yr (2σ), respectively. Although the intermediate solution covers the full range of ages for the measured displacements, the curved geometry of the terrace risers suggests that the initiations of the riser offsets are most probably close to the abandonment ages of the upper terrace treads. Therefore, we accepted the joint slip rate of the intermediate solution but suggested that the average rate for the main displacement zone of the eastern NAF should be close to its lower limits. This slower rate with respect to previous estimates suggests that the total deformation is not only accommodated on the main displacement zone but is also distributed along the secondary faults to the south of the easternmost segments of the NAF.

Mechanics of plio-quaternary faulting around the Karliova triple junction: implications for the deformation of Eastern part of the Anatolian Scholle

ABSTRACT The intersection of the Eurasian and Arabian plates and the smaller Anatolian Scholle created the Karlıova Triple Junction (KTJ) in eastern Turkey. In this study, we present analogue model experiments for this region and compare the results with our field observations and data from remote sensing imagery. Our comparison suggests that the sense of slip along curvilinear faults at the west of the KTJ changes along strike moving away from the principal displacement zones, from strike-slip to oblique normal and then to pure normal slip. Although, the active Prandtl cell model has been proposed to explain the overall regional fault pattern at eastern part of the Anatolian Scholle, the map view orientation of the secondary faults within the Karlıova wedge and performed analogue modelling results suggest that the passive wedge-shaped Prandtl cell model with a normal dip-slip component along slip lines is more appropriate in order to explain not only deformation pattern around the KTJ but also internal deformation of eastern part of the Anatolia. Moreover, these faults accumulate the significant amount of deformation that causes to the irregular earthquake behavior and the relatively lower geologic slip-rates along the main fault branch of boundary faults around the KTJ. Abbreviations: Strike-slip; Karlıova Triple Junction (KTJ); continental deformation; North Anatolian Fault Zone (NAFZ); East Anatolian Fault Zone (EAFZ);Varto Fault Zone (VFZ)