| Paleoseismologic trenches excavated across the North Anatolian fault in Turkey are used to characterize the spatial-temporal pattern of seismic moment release on this plate-bounding strike-slip fault. Trenches at Alayurt reveal evidence for at least four (possibly five) surface ruptures during the past 2,000 years, and one older event: (1) the historic 1943 Tosya earthquake; (2) the great 1668 earthquake; (3) a late 8th--early 13th century earthquake; (4) a 1st to 3rd century AD earthquake (historic 236 event?); (5) a possible earthquake between late 4th and early 11th centuries AD; and (6) a BC 4600--3550 event.; Trenches at Cukurcimen yield a complete record of surface ruptures for the past 2,500 years. Mutually consistent evidence constrains the timing of the five most-recent (and two older) surface ruptures: the historic 1939, 1254, and 1045 AD earthquakes; an earthquake that occurred 250--540 AD (historic 499 earthquake?); and a 770--50 BC (probably 230--50 BC) earthquake. One additional earthquake occurred 1450--800 BC, and at least one other occurred 2880--200 BC.; Trenches at Ulaslar reveal evidence for three earthquakes: the 1944 Bolu-Gerede, the great 1668, and the historic 1050 AD earthquakes.; Trenches at Yukaribercin, Gunalan, and Kocyatagi exposed the fault, but no useful paleoseimologic data were obtained.; My findings, coupled with other published results, enable construction of a space-time earthquake history for the North Anatolian fault. Striking aspects of this analysis include: (1) rarity of earthquakes along the central-eastern section of the fault, suggesting that large, infrequent events are the norm; (2) earthquake occurrence is temporally regular (∼200- to <900-year recurrence, varying by a factor of only 3 to 4) along the central-eastern section of the fault; and (3) almost the entire length of the fault ruptured in short-lived activity clusters in the 17th --18th and 10th--12th centuries. The magnitude and sequence of individual ruptures has varied between clusters, however. The North Anatolian fault does not always rupture in sequences similar to the 20th century. Quasi-periodic, large, infrequent earthquakes appear to be the norm for the North Anatolian and San Andreas faults, at least in the absence of structural and stress evolution/loading-history complexities. In contrast, the parts of these faults within more tectonically complex regions exhibit more frequent, smaller-displacement, more temporally random earthquakes.; Finally, I describe my surface rupture mapping of the 17-August-1999 Mw7.4 Izmit and 12-November-1999 Mw 7.1 Duzce, Turkey earthquakes. |
