Historical Earthquake Scenarios for the Middle Strand of the North Anatolian Fault Deduced from Archeo-Damage Inventory and Building Deformation Modeling

Abstract

The city of İznik (ancient Nicaea), located on the middle strand of the North Anatolian fault zone (MNAF), presents outstanding archeological monuments preserved from the Roman and Ottoman periods (first to fifteenth centuries A.D.), bearing deformations that can be linked to past seismic shaking. To constrain the date and intensity of these historical earthquakes, a systematic survey of earthquake archeological effects (EAEs) is carried out on the city’s damaged buildings. Each of the 235 EAEs found is given a quality ranking, and the corresponding damage is classified according to the European Macroseismic Scale 1998 (EMS-98). We show that the walls oriented north–south were preferentially damaged, and that most deformations are perpendicular to the walls’ axes. The date of postseismic repairs is constrained with available archeological data and new C14 dating of mortar charcoals. Three damage episodes are evidenced: (1) between the sixth and late eighth centuries, (2) between the nineth and late eleventh centuries A.D., and (3) after the late fourteenth century A.D. The repartition of damage as a function of building vulnerability points toward a global intensity VIII on the EMS-98. The 3D modeling of a deformed Roman obelisk shows that only earthquakes rupturing the MNAF can account for this deformation. Their magnitude can be bracketed between Mw 6 and 7. Our archeoseismological study complements the historical seismicity catalog and confirms paleoseismological data, suggesting several destructive earthquakes along the MNAF, since the first century A.D. We suggest the fault might still have accumulated enough stress to generate an Mw 7+ rupture.

Active Subaquatic Fault Segments in Lake Iznik Along the Middle Strand of the North Anatolian Fault, NW Turkey

“…CE and thus coincides with the well‐documented 1065 CE earthquake (Ambraseys, 2009). The independent archeo‐seismological study of Benjelloun et al (2020), documents an important phase of reconstruction of Nicaea's buildings (formerly Iznik) between 858 and 1097 CE. According to the original historical archive (Michael & Attaleiatēs, 2012), the 1065 CE earthquake has strongly damaged the city of Iznik (formerly Nicaea/Nikaia): “It happened at Nikaia in Bithynia and brought almost total devastation and ruin to the place.…”

“…At least 15 earthquakes were documented in historic chronicles in Iznik during the last two millennia (Ambraseys, 2002;Ambraseys & Finkel, 1991;Ambraseys & Jackson, 2000;Benjelloun et al, 2020). According to these archives, the epicenter of some of them is located on the MNAF (29-32; 121; 368 and 1,065; the 1419 CE earthquake was also recorded on the SNAF so the epicenter location is still under debate).…”

“…This long quiescence strongly contrasts with a significant historical tectonic activity on the MNAF. Several chronicles and archeological studies report the partial destruction of the city of Iznik (previously called Nicaea) and surrounding areas following~15 major earthquakes within the last 2,000 years with unknown rupture segments (Ambraseys, 2002;Ambraseys & Finkel, 1991;Ambraseys & Jackson, 2000;Benjelloun et al, 2020). The quiescence of the MNAF in recent times may hide a longer seismic recurrence, which possibly is just as hazardous as the NNAF (according to their span of quiescence), but has been underestimated by the models.…”

Active subaquatic fault segments in Lake Iznik along the middle strand of the North Anatolian Fault, NW Turkey

“…At least fifteen earthquakes were documented in historic chronicles in Iznik during the last two millennia, (Ambraseys & Finkel, 1991;Ambraseys & Jackson, 2000;Ambraseys, 2002;Benjelloun et al, 2020).…”

“…Several chronicles and archaeological studies report the partial destruction of the city of Iznik (previously called Nicaea) and surrounding areas following ~ 15 major earthquakes within the last 2000 years with unknown rupture segments (Ambraseys & Finkel, 1991;Ambraseys & Jackson, 2000;Ambraseys, 2002;Benjelloun et al, 2020). The quiescence of the MNAF in recent times may hide a longer seismic recurrence, which possibly is just as hazardous as the NNAF (according to their span of quiescence), but has been underestimated by the models.…”