Historical Seismograms - Evidence from the AD 2000 Izu Islands ...

The Anatolian Earthquake of 17 August 1668 1774. DiscussionAlthough it is impossible at this stage to assess the effects of this earthquake onthe towns of Anatolia in greater detail, it is quite clear that the event may havebeen comparable to, if not larger than, the 1939 earthquake in the extent of the areaaffected and the number and duration of foreshocks and aftershocks experienced.From Figure 1, we notice that part of the area affected was on the main caravanroute through northern Anatolia (Taeschner, 1926; Taeschner, 1960), which formuch of its length ran along the North Anatolian fault zone, extending from Boluin the west to past Koyulhisar, to Erzincan in the east, a distance of 680 km, as issuggested not only by the considerable damage to Bolu in the west and to a lesserextent to Erzincan in the east, but also by the ground deformation reported fromthe regions of Kochisar, Zara and Amasya that coincide with more recent faultbreaks (Ketin, 1969). It would appear that the area affected extended into themountainous rural area of Sivas and further to the east toward Erzincan, as well asto the north along the Black Sea coast.The surface-wave magnitude of this earthquake may be assessed from the magnitudefault length relationships for earthquakes in the Middle East (Ambraseys,1986). Assuming a 400 km long rupture and average dislocation of the orderof the rupture length, we find that Ms = 8.0. Alternatively we may use the averageradius of the isoseismal VI (MSK) shown in Figure 1, i.e. r,i = 270 km, andEquation (1) in Ambraseys and Melville (1986). This would give Ms = 7.8. Thus,as a first approximation, the magnitude of the 1668 North Anatolian earthquakeshould have been close to 8.0. The casualties, in excess of 8,000, would have beenmuch greater had the people not been warned by the protracted foreshock period.It is rather strange that this apparently major event seems not to be mentioned bymany contemporary Ottoman sources for this period, which is otherwise relativelywell-documented. The search for additional details of this event goes on.ACKPTOWLEDGEMENTSThis research project is supported by a Natural Environment Research Councilgrant for the study of the historical seismicity of the eastern Mediterranean region.REFERENCESAmbraseys, N. N. (1975). Studies in historical seismicity and tectonics, GeodynamicsToday, Royal SOC. Publ., London.Ambraseys, N. N. (1986). Magnitude-fault length relationships for earthquakes in theMiddle East, this volume.Ambraseys, N. N. and C. P. Melville (1986). An analysis of the eastern Mediterraneanearthquake of 20 May 1202, this volume.d’Aramon, see Chesneau below.Burnaby, F. (1877). On horseback through Asia Minor, v. 2, 307 pp., London.Calvi, V. S. (1941). Erdbebenkatalog der Tiirkei and einiger Benachbarter Gebiete, &portn.276 of M.T.A. Enstitiisii (unpub.), Ankara. (not seen)Chesneau, Jean‘ (1887). Le voyage de Monsieur d’Aramon ambassadeur pour le roy enLevant, Recueil de Voyages et de Documents, Histoire de la Geographie, v. 8, pp. 64,G5, 71, Annot. Ch. Schefer. Paris.