Abstract
This paper provides a new contribution to the construction of the complex and fragmentary mosaic of the Late Holocene earthquakes history of the İznik segment of the central strand of the North Anatolian Fault (CNAF) in Turkey. The CNAF clearly displays lower dextral slip rates with respect to the northern strand however, surface rupturing and large damaging earthquakes (M > 7) occurred in the past, leaving clear signatures in the built and natural environments. The association of these historical events to specific earthquake sources (e.g., Gemlik, İznik, or Geyve fault segments) is still a matter of debate. We excavated two trenches across the İznik fault trace near Mustafali, a village about 10 km WSW of İznik where the morphological fault scarp was visible although modified by agricultural activities. Radiocarbon and TL dating on samples collected from the trenches show that the displaced deposits are very recent and span the past 2 millennia at most. Evidence for four surface faulting events was found in the Mustafali trenches. The integration of these results with historical data and previous paleoseismological data yields an updated Late Holocene history of surface-rupturing earthquakes along the İznik Fault in 1855, 740 (715), 362, and 121 CE. Evidence for the large M7 + historical earthquake dated 1419 CE generally attributed to this fault, was not found at any trench site along the İznik fault nor in the subaqueous record. This unfit between paleoseismological, stratigraphic, and historical data highlights one more time the urge for extensive paleoseismological trenching and offshore campaigns because of the high potential to solve the uncertainties on the seismogenic history (age, earthquake location, extent of the rupture and size) of this portion of NAFZ and especially on the attribution of historical earthquakes to the causative fault.
Highlights
The North Anatolian Fault Zone (NAFZ) is an east–west trending, ∼1500 km long right-lateral strike-slip fault that extends from the northern Aegean Sea to the Karliova triple junction in Eastern Turkey (Barka 1992; Sengör et al 2005; McKenzie 1972; Saroglu et al 1992; Emre et al 2018—inset of Fig. 1a) and accommodates the relative motion of the
Gemlik and its vicinity (on land faults from Emre et al (2011, 2018); Gemlik bay faults and bathymetry from Kuşçu et al 2009; İznik Lake bathymetry from Ikeda et al 1991; İznik Lake underwater faults modified from Gastineau et al 2021; seismological data from Kalafat et al 2011)
The segment boundary between the İznik and Gemlik segments near Sölöz, is rather complex with several traces forming a continuous broad releasing bend (~ 5 km long and ~ 2 km wide) that links the stepover invoked to act as a barrier to the rupture propagation (e.g., Koçyiğit 1988; Emre et al 1998; Özalp et al 2013) (Fig. 1b, c)
Summary
The North Anatolian Fault Zone (NAFZ) is an east–west trending, ∼1500 km long right-lateral strike-slip fault that extends from the northern Aegean Sea to the Karliova triple junction in Eastern Turkey (Barka 1992; Sengör et al 2005; McKenzie 1972; Saroglu et al 1992; Emre et al 2018—inset of Fig. 1a) and accommodates the relative motion of the. The segment boundary between the İznik and Gemlik segments near Sölöz, is rather complex with several traces forming a continuous broad releasing bend (~ 5 km long and ~ 2 km wide) that links the stepover invoked to act as a barrier to the rupture propagation (e.g., Koçyiğit 1988; Emre et al 1998; Özalp et al 2013) (Fig. 1b, c). This fault setting would open questions on the role of segment boundaries as permanent barriers to earthquake ruptures. To contribute with one more tile to the earthquake history along the CNAF, we conducted a geomorphologic and paleoseismic campaign along the western portion of the İznik Fault (Fig. 1b,c)
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