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

Abstract

<p>Lake Iznik (NW Turkey), is bordered by the middle strand of the North Anatolian Fault (MNAF), whose seismic activity is debated because of its quiescence during the instrumental period. In contrast, significant historical activity is documented by several chronicles over the last two millennia.</p><p>This study aims to get a new insight into its long-term seismicity and its tectonic setting. Lacustrine sediment cores reveal fourteen earthquake-induced turbidites since their ages correspond to seismic events during the past two millennia. Bathymetry and high-resolution seismic reflection data allow describing two hitherto unknown subaquatic active fault structures (the South Boyalica and Iznik faults), belonging to the MNAF system. Sediment cores sampled on both sides of the Iznik Fault document an event deposit and a sedimentary unit vertically offset of ∼ 40 cm interpreted as the last rupture during the 1065 CE destructive earthquake. Older events are supposed on this fault more than a thousand years ago. Further studies will help to estimate the horizontal coseismic offset of this oblique-slip fault and the calendar of older ruptures. The current seismic gap of thousand years on this segment greatly increases the seismic hazard in this region and must be considered in the seismic risk assessment of the NAF system.</p>

Segmentation and Holocene Behavior of the Middle Strand of the North Anatolian Fault (NW Turkey)

“…(2009) suggested the existence of a continuous strike‐slip fault extending along the deepest area of Iznik Lake, while Gastineau et al. (2021) evidenced an active fault strand following the northeastern edge of the lake's southern sub‐basin, in a pull‐apart configuration (Figure 3b). East of Iznik Lake, Sipahioglu and Matsuda (1986) reported the presence of two lineaments in this section: a geological boundary fault with no marker of Quaternary activation, and an active fault strand crosscutting and deforming recent alluvium.…”

“…In the eastern part of Iznik Lake, Gastineau, et al. (2021) evidenced a historical event in sediment cores, that they correlated to the 1065 CE earthquake. South of the lake, Erginal et al.…”

“…The subaqueous fault trace is taken from Gastineau et al. (2021). The eastern limit of terrace T3 is not well defined in the geomorphology and was drawn assuming a constant elevation.…”

“…The fault traces within Iznik Lake are taken from Gastineau et al. (2021). (b) Segmentation of the main fault section analyzed in this study.…”

“…To estimate this length, we rely on the magnitude estimated by historical seismology studies (see Table S1), from which a surface rupture length was derived using the relationship of Wells and Coppersmith (1994). The length of the vertical boxes corresponds to the dating of the events within 2σ uncertainty (Civico et al., 2021; Dikbas et al., 2018; Dogan, 2010; Gastineau et al., 2021; Honkura & Isikara, 1991; Ikeda, Suzuki, et al., 1991; Klinger et al., 2003; Özalp et al., 2013; Rockwell et al., 2009; see Table S2 for detailed data).…”