Northern segment of the North Anatolian Fault in the Gulf of Izmit inferred from marine magnetic anomalies

Demirel, Sinan; Alpar, Bedri; Yaltırak, Cenk; Vardar, Denizhan; Kurt, H.

doi:10.1007/s11001-020-09399-6

Cited by 12 publications

(6 citation statements)

References 30 publications

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“…The description of the whole active fault system in and around Lake Iznik also improves tectonic knowledge. The Gürle and Orhangazi normal faults bounded the underwater Iznik and South Boyalıca faults, resulting in a negative flower structure linked to the MNAF system, as shown on the simplified NS cross section of the lake (Demirel et al, 2020; Figure 10b). Lake Iznik exhibits three sub‐basins that cannot be explained in a simple pull‐apart process approach (Dooley & Schreurs, 2012; Wu et al, 2009).…”

Section: Discussionmentioning

confidence: 99%

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

et al. 2021

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The seismic activity of the middle strand of the North Anatolian Fault (MNAF), Northwestern Turkey, is debated because of its quiescence during the instrumental period, in contrast to a significant historical activity documented by several chronicles over the last two millennia. Here, we focus on Lake Iznik, bordered by the MNAF, to get a new insight into its long-term seismicity and its tectonic setting. The study of lacustrine sediment cores reveals 14 earthquake-induced turbidites since their ages correspond to seismic events during the past two millennia. Bathymetry and high-resolution seismic reflection data allow to describe two hitherto unknown subaquatic active fault structures (the South Boyalica and Iznik faults) that belong 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 thousand years ago. Further studies will help to estimate the horizontal co-seismic 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. Plain Language Summary During large earthquakes, sediments are generally transported from lake slopes to the lake basin. The resulting event deposits can provide information on the recurrence of past regional earthquakes, which is crucial for seismic hazard assessment. In this study, we discovered two underwater fault structures in Lake Iznik, using geophysical methods. Studying the sedimentation on both sides of the southernmost fault, we observed an increased sedimentation rate on the hanging wall of the fault immediately after an event deposit, dated to 1077 ± 77 cal. CE. We interpreted these indicators as resulting from a co-seismic displacement along the fault plane, linked to the 1065 CE historical earthquake, which had significantly impacted the city of Iznik. We also show that most of the other event deposits in the sediment cores are confidently associated to 14 historical earthquakes since 2,000 years.

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Section: Discussionmentioning

confidence: 99%

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

et al. 2021

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“…The Gürle and Orhangazi normal faults bounded the underwater Iznik and South Boyalıca faults, resulting in a negative flower structure linked to the MNAF system, as shown on the simplified NS cross section of the lake (Demirel et al, 2020;Fig. 10b).…”

Section: Regional Tectonicsmentioning

confidence: 99%

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

Gastineau

Sigoyer

Sabatier

et al. 2021

Preprint

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Key points:1. Previously unknown faults that belong to the North Anatolian Fault system have been discovered in Lake Iznik through geophysical surveys (from multibeam bathymetry and high-frequency seismic reflection data).2. Assessment of the recent activity of the Iznik Fault, based on multiproxy analysis of sediment cores from each side of the fault.3. Evidence for the timing of the last rupture corresponding to the 1065 CE historical earthquake, which had significantly impacted the city of Iznik.

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“…In these cases, geophysical surveys can give additional evidences [Barberi et al, 2004;Schrott and Sass, 2008;Blaikie et al, 2014], and among them, the magnetic investigation has been widely and efficaciously used in detecting concealed and subsurface volcano-tectonic structures. The interpretation of magnetization contrasts, appropriately integrated with the available geophysical and geological knowledge of the investigated area, has provided valid information on the relationships between the various volcanic and/or tectonic structures both at local and regional level worldwide [Finn and Morgan, 2002;Blanco-Montenegro et al, 2003;Napoli et al, 2007;Napoli and Currenti, 2016;Caratori Tontini, 2016;Demirel et al, 2020;Yan et al, 2018]. In volcanic areas, indeed, the strong magnetization contrasts generated by the presence of rocks with different magnetic properties (susceptibility, induced and remanent magnetization) make this method and the related anomaly maps an efficient tool to identify, delineate, and estimate the depth of the subsurface complex structures.…”

Section: Introductionmentioning

confidence: 99%

Magnetic signatures of subsurface faults on the northern upper flank of Mt Etna (Italy)

Napoli

Currenti²,

Sicali³

2021

Annals of Geophysics

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A ground magnetic study was performed on the northern upper flank of Mt. Etna to provide new insights into subsurface volcano-tectonic structures. The high resolution magnetic survey was focused on the main structures of Piano delle Concazze, a large flat area dominated by the North- East crater and bounded by the rim of the Valle del Leone depression and the extremity of the North- East Rift. More than 2,500 measurements were gathered with a sampling step of about 3 m covering an area of about 0.2 km2. The total-intensity anomaly field shows the presence of intense South- North aligned maxima related to shallow geological structures affecting this area. Filtering techniques and 2.5D modeling have been applied for the determination of the magnetic source parameters. In order to distinguish the near surface structure, filters of the vertical derivatives, Butterworth high-pass and the tilt derivative were used. The 3D Euler deconvolution has been applied to estimate the depth and the structural indices of the causative sources. The calculated structural indices, that express the geometrical nature of the source, are in agreement with forward modeling. They show that the area is mainly affected by subvertical normal fault and the estimated depth of magnetic sources ranges between 10 m and 40 m. Our total field magnetic survey shows that characteristic magnetic anomalies are related to fault zones in the Piano delle Concazze that are well consistent with the local tectonics. The subsurface structures that have been detected allowed to delineate the general structural framework of the area. In particular, it was possible to clarify that these structures seem to be not deep rooted and consequently they can hardly act as preferential pathways for magma ascent.

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Northern segment of the North Anatolian Fault in the Gulf of Izmit inferred from marine magnetic anomalies

Cited by 12 publications

References 30 publications

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

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

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

Magnetic signatures of subsurface faults on the northern upper flank of Mt Etna (Italy)

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