Ömer Emre

Submarine fault scarps in the Sea of Marmara pull-apart (North Anatolian Fault): Implications for seismic hazard in Istanbul

Earthquake scarps associated with recent historical events have been found on the floor of the Sea of Marmara, along the North Anatolian Fault (NAF). The MARMARASCARPS cruise using an unmanned submersible (ROV) provides direct observations to study the fine-scale morphology and geology of those scarps, their distribution, and geometry. The observations are consistent with the diversity of fault mechanisms and the fault segmentation within the north Marmara extensional step-over, between the strike-slip Ganos and Izmit faults. Smaller strike-slip segments and pull-apart basins alternate within the main step-over, commonly combining strike-slip and extension. Rapid sedimentation rates of 1?3 mm/yr appear to compete with normal faulting components of up to 6 mm/yr at the pull-apart margins. In spite of the fast sedimentation rates the submarine scarps are preserved and accumulate relief. Sets of youthful earthquake scarps extend offshore from the Ganos and Izmit faults on land into the Sea of Marmara. Our observations suggest that they correspond to the submarine ruptures of the 1999 Izmit (Mw 7.4) and the 1912 Ganos (Ms 7.4) earthquakes. While the 1999 rupture ends at the immediate eastern entrance of the extensional Cinarcik Basin, the 1912 rupture appears to have crossed the Ganos restraining bend into the Sea of Marmara floor for 60 km with a right-lateral slip of 5 m, ending in the Central Basin step-over. From the Gulf of Saros to Marmara the total 1912 rupture length is probably about 140 km, not 50 km as previously thought. The direct observations of submarine scarps in Marmara are critical to defining barriers that have arrested past earthquakes as well as defining a possible segmentation of the contemporary state of loading. Incorporating the submarine scarp evidence modifies substantially our understanding of the current state of loading along the NAF next to Istanbul. Coulomb stress modeling shows a zone of maximum loading with at least 4?5 m of slip deficit encompassing the strike-slip segment 70 km long between the Cinarcik and Central Basins. That segment alone would be capable of generating a large-magnitude earthquake (Mw 7.2). Other segments in Marmara appear less loaded.

Sea-level changes and depositional environments in the İzmit Gulf, eastern Marmara Sea, during the late glacial–Holocene period

Abstract Offshore and onshore stratigraphic studies, together with high-resolution shallow seismic reflection profiling and multibeam bathymetric mapping, were carried out in the western and central part of the Izmit Gulf. These studies indicate that the Izmit Gulf was a lacustrine environment as part of the Marmara ‘Lake’ during the late glaciation and early deglaciation until ∼12 kyr BP, when the Marmara Basin was inundated by the Mediterranean waters. Correlation of 14 C-dated onshore and offshore stratigraphic units in the Western Izmit Gulf indicates that generally coarse late glacial sediments overlie a marked erosional surface formed during the low water level of the Marmara ‘Lake’. These coarse sediments are succeeded by 10.4–7 kyr BP old transgressive, and by late Holocene post-transgression mud units. The bathymetry and sub-bottom Chirp profiles clearly show that the paleoshoreline of the Gulf was located at −85 m, having been controlled by the bedrock sill depth of the Canakkale Strait. Another paleoshoreline observed at −65 m on the northern margin of the Western Izmit and Karamursel basins was probably formed during the Younger Dryas sea-level stillstand. The shelf areas during this time were colonized by bioherms, which were subsequently drowned and disappeared after a further rise of the sea level. The presence of a −65 m marine paleoshoreline in the Karamursel Basin indicates that the sill restricting this basin to the west was much deeper than its present −55 m level and was located further south. The Golcuk Basin, restricted by a −38 m sill to its west, was probably not flooded by marine waters until ∼9 kyr BP.

Abrupt environmental changes within a late Holocene lacustrine sequence south of the Marmara Sea (Lake Manyas, N-w Turkey): possible links with seismic events

Abstract A coring campaign in Lake Manyas (Kus Golu) on the southern coast of the Sea of Marmara (Turkey) has provided insights into basin infilling processes during the upper 11 metres of the sedimentary record. Combined sedimentary features between 5 and 4 m depth have been explained by a seismite. A brittle mixed layer (uniquely rich in seeds and ostracod valves) was widely detected at 4 m downcore. This has been interpreted as being the result of a seiche either through a salt inundation linked to a tsunami in the Sea of Marmara (the large-scale scenario) or a local hydrothermal fluid discharge (the small-scale scenario). Ostracod valves, which are usually not preserved in Lake Manyas sediment, are either incorporated here as tsunami debris (providing a spatially averaged snapshot of the regional assemblage) or are locally preserved following a temporary geochemical/hydrochemical change of the water of unknown duration (but probably several decades). The brittle mixed layer overlies cracks resulting from the direct effects of the seismic shock wave on slightly compacted sediment. At around 964 cm depth palynological and particle-size analyses indicate a change from backswamp to open lacustrine conditions. The end of the backswamp has been correlated with a decrease in the level of the Sea of Marmara from 4000 to 3000–2800 yr ago (uncal.), caused by regional tectonic movements. An age–depth model is presented based on two AMS radiocarbon dates, on the palynological detection of the end of the Beysehir Occupation Phase (130 cm above the event) and on maximal sedimentation accumulation rates obtained by radionuclide analyses. The entire study sequence covers the last 4300 yr. The paper examines the possibility of an Early Byzantine age for the seismic event. This may have been the historical event at AD 460 that destroyed Cyzicus (the ancient Erdek, 20 km north of the lake) and various villages in the interior and was felt widely in the then-known world. Other possibilities include various local and regional events in that same period: the Early Byzantine Tectonic Paroxysm and the large earthquake in AD 447 that affected the entire Sea of Marmara region.

Slip Distribution, Fault Geometry, and Fault Segmentation of the 1944 Bolu-Gerede Earthquake Rupture, North Anatolian Fault, Turkey

The 1944 Bolu-Gerede earthquake ( M s 7.3) occurred along the North Anatolian fault in northern Turkey and ruptured for about 180 km of the fault. The surface slip distribution and fault geometry, which provide fundamental data on detailed fault segmentation and recurrence of faulting during a multisegment rupture, are poorly known for this event. We conducted geomorphological and geological investigations and eyewitness interviews to determine cumulative offsets through several earthquake cycles. The 1944 rupture comprised five fault segments based on slip distribution and fault step-overs and bends. From west to east, they are called the Bolu, Yenicaga, Gerede, Ismetpasa, and Bayramoren segments. The segments were 21 to 46 km long, and the average slip was 1.9–4.3 m, similar to well-examined segments of the 1999 Izmit rupture. In contrast, the fault jogs were relatively small, suggesting that the 1944 earthquake rupture process was relatively smooth and of short duration. Proposed fault segmentation is consistent with the extent of surface ruptures and damage intensity associated with historical earthquakes in 967, 1035, and 1050 a.d. Historical records indicate that the Bolu and Yenicaga segments ruptured in 967 a.d., and the Gerede, Ismetpasa, and possibly, Bayramoren segments ruptured in 1035 a.d. Therefore, the 1944 rupture occurred as a consequence of multisegment rupture, which consists of at least two distinct earthquake segments. Along the Gerede segment, which slipped 3 to 6 m in 1944, cumulative offsets of 6 to 25 m were observed. These offsets are double, triple, and quadruple multiples of the 1944 slip, implying a similar slip distribution during the four most recent large earthquakes along this segment and supporting the concept of characteristic slip, even though the rupture length varied greatly during the last four earthquake cycles.

Step-Over and Bend Structures along the 1999 Duzce Earthquake Surface Rupture, North Anatolian Fault, Turkey

The 12 November 1999 Duzce earthquake (M w 7.1), which occurred on the Duzce fault of the North Anatolian Fault Zone, formed a 40-km-long surface rupture, which extended between Golyaka in the west and Kaynasli in the east. The earthquake nucleated close to the Beykoy step-over, a 0.8-km-wide and 1.8-km-long pressure ridge, with bilateral rupture propagation both to the west and the east. The Beykoy, Kaynasli, and Cevizlik step-overs, through which the 1999 Duzce rupture propagated, are less than 2.5 km wide. The Eften and Bakacak step-overs, where the rupture was arrested, are more than 4 km wide. These exceptional dimensions of step-overs associated with the 1999 Duzce rupture were investigated for their influ- ence on rupture propagation. The earthquake broke three distinct geometric segments, from west to east, the Eften, Dagdibi, and Kaynasli fault segments, separated by left-restraining step-overs at Beykoy and Kaynasli. To the west of the main shock, 3.5 m of average slip on the Eften fault segment propagated into the 2-km-wide Cevizlik releasing double bend, where it was largely arrested, with smaller (0.5 m) slip continuing westward on the Golyaka intervening segment, west of Lake Eften. This is similar to the ter- mination of slip observed on the Karadere fault segment in the 1999 Izmit earthquake, where 1.5 m of slip was largely terminated by a releasing double bend at the Golyaka intervening segment, with minor slip continuing eastward near Lake Eften. To the east of the main shock, 5 m of slip decreased along the Dagdibi fault segment to about 3.5 m at the 1-km-wide Kaynasli step-over. From here to the east, the 2.5 m of average slip on the Kaynasli fault segment continued to decrease, reaching zero at the releasing step-overs to the Elmalik fault. The terminations of the 1999 Duzce surface rupture are defined by distinct struc- tural complexities. The rupture was arrested in the west at the 4-km-wide Eften releasing double bend, where the eastern termination of the 1999 Izmit rupture also occurred. To the east, the rupture terminated at the 4- to 5-km-wide Bakacak releasing double step-overs. Both eastern and western ends of the Duzce rupture have short fault segments that experienced minor rupture during the 1999 Duzce earthquake. The Golyaka intervening segment experienced minor rupture, during both the 1999 Izmit and Duzce earthquakes. The Duzce rupture propagated across 0.8- to 2-km- wide step-overs, but it was arrested at step-overs 4 km wide or wider. These results agree with the observations on ratios between step-over width (in kilometers) and strike-slip displacement (in meters) collected along strike-slip faults worldwide (Let- tis et al., 2002).

Rapid subsidence and sedimentation from oblique slip near a bend on the North Anatolian transform fault in the Marmara Sea, Turkey

Several basins are developing near bends on strands of the North Anatolian transform fault in northwest Turkey. Oblique slip on these faults, rather than strain partitioning, accounts for trans- tension and subsidence. These basins are asymmetric, and tilt and subside most rapidly at their narrow ends near the bends. The turbidite surface marking the floor of the Cinarcik Basin (eastern Marmara Sea) was mostly abandoned at a sudden drop in sedi- mentation, which was likely coincident with the 14 ka lake-sea transition, and is now a warped reference surface from which we can measure strain and sedimentation. Subsidence and tilt are rap- id, but do not require late Quaternary changes in regime. They are linked to transcurrent motion by slip parallel to an oblique bend on the North Anatolian fault and suggest tsunamogenic ver- tical motion in large Marmara Sea earthquakes.

The rodent fauna from the Adapazarı pull-apart basin (NW Anatolia): its bearings on the age of the North Anatolian fault

AbstractTo the east of the Sea of Marmara, the North Anatolian fault (NAF) branches into two strands, namely the northern and the southern strands. The Adapazan pull-apart basin is located in the overlapping zone of the Dokurcun and the Izmit-Adapazan segments of the northern strand. The combined temporal ranges of the arvicolids from the Karapurcek formation (the first unit of the basin fill), deposited in the primary morphology of the Adapazan pull-apart basin, cover the latest Villanyian (latest Pliocene) and the Biharian (Early Pleistocene) time interval. The Degirmendere fauna collected from the lowermost sediments of this formation suggests that the Adapazan pull-apart basin started to form in the latest Pliocene. This, in turn, suggests that the dextral movement along the northern strand of the NAF commenced during the latest Pliocene. A new species, Tibericola sakaryaensis is also described.

The East Anatolian Fault: geometry, segmentation and jog characteristics

Abstract A detailed account is given of the fault geometry and segment structure of the East Anatolian Fault Zone as a whole based on mapping of active faults, supported by available seismological and palaeoseismological data. We divide the East Anatolian Fault into two main strands: southern and northern. The main southern strand is c. 580 km long between Karlıova and Antakya, and connects with the Dead Sea Fault Zone and the Cyprus Arc via the Amik triple junction. The northern strand, termed the Sürgü–Misis Fault system, is c. 350 km long and connects with the Kyrenia–Misis Fault Zone beneath the Gulf of İskenderun. We infer that slip partitioning between the main and northern strands of the East Anatolian Fault accommodates 2/3 and 1/3 of the slip rate of the lateral motion between the Arabian and Anatolian plates, respectively in the Çelikhan–Adana–Antakya region. Taking account of the time elapsed from the latest events on the East Anatolian Fault, we suggest that the Pazarcık and Amanos segments have the potential to produce destructive earthquakes in the near future. Supplementary material: The data and interpretations given here are supported by five additional annotated field photographs and two tables of factual data, these are available at www.geolsoc.org.uk/SUP18568

Seismotectonic database of Turkey

Turkey is located in one of the most seismically active regions in the world. Characterizing seismic source zones in this region requires evaluation and integration of geological, geophysical, seismological and geodetical data. This first seismotectonic database for Turkey presented herein was prepared, under the framework of the National Earthquake Strategy and Action Plan—2023. The geographic information system (GIS)-based database includes maps of active faults, catalogues of instrumental and historical earthquakes, moment tensor solutions and data on crustal thickness. On the basis of these data, 18 major seismotectonic zones were delineated for Turkey and the surrounding region. The compilation and storage of the seismotectonic data sets in a digital GIS will allow analyses and systematic updates as new data accrete over time.

GÜNEY MARMARA BÖLGESİNDEKİ BÜYÜK VADİLERİN OLASI DEŞİLME ZAMANI

Surface water and sediments derived from the southern Marmara region (= SusurlukDrainage basin- SDH) transport to lakes Manyas and Ulubat first and then go to the Sea ofMarmara via the Kocasu River only. The present drainage system of the SDH provides a goodopportunity to study erosion rate and subsequently occurrence times of large-scale valleys inthe region. To achieve it, depositional characteristics and ion contents of the ancientlacustrine sediment has been investigated and re-interpreted using cores taken from LakeUlubat. The boron content of these sediments increased upward suddenly at the 4 m level,most probably due to starting of erosion at Emet borate beds in the drainage basin. Takinginto consideration equilibrium between natural erosion and sedimentation, the incision ratein the Emet valley was found 1.4 cm.yr-1. From here one can calculate a time span of 75 kyfor the formation of the whole valley itself. However, it is known that working of the geologicalprocesses was not monotonous in the past; hence, this date is not absolute. Newertheless,formation of the large valleys of the southern Marmara region shouldn’t be older than 300kyrs. An important reason on rapid erosion was likely lowered base-level as the Marmara Seawas a closed lake during the last Glacial Period. High altitudinal difference between sourceand depositional areas caused acceleration of the erosion.1. Girifl