Bedri Alpar

Tsunamis in the Sea of Marmara: Historical documents for the past, models for the future

Abstract More than 30 tsunami events have impacted the coasts of the Sea of Marmara in the past two millennium, clustering in Izmit Bay, the shores of Istanbul, Gemlik Bay, the shores of the Kapidag and Gelibolu Peninsulas. With respect to the last well-known tsunami, the Izmit tsunami of 17 August, 1999, available field survey run-up data and marine surveys provide an opportunity to evaluate how these events were triggered. The main purpose of this study is to determine the slope failure potential as a possible tsunamigenic source in the Sea of Marmara by utilising multi-beam bathymetry, shallow and deep seismic reflection data. On the basis of the landslide geomorphology, the generation, propagation and coastal amplifications of tsunamis related to earthquake and slope failure scenarios were tested by using tsunami simulation model TWO_LAYER. The maximum water surface elevations near the shores along the north and south coasts are obtained according to the selected scenarios of tsunami generation by using available data.

Tectonic elements controlling the evolution of the Gulf of Saros (northeastern Aegean Sea, Turkey)

Abstract Tectonic elements controlling the evolution of the Gulf of Saros have been studied based upon the high-resolution shallow seismic data integrated with the geological field observations. Evolution of the Gulf of Saros started in the Middle to Late Miocene due to the NW–SE compression caused by the counterclockwise movement of the Thrace and Biga peninsulas along the Thrace Fault Zone. Hence, the North Anatolian Fault Zone is not an active structural element responsible for the starting of the evolution of the Gulf of Saros. The compression caused by the rotational movement was compensated by tectonic escape along the pre-existing Ganos Fault System. Two most significant controllers of this deformation are the sinistral Ganos Fault and the dextral northern Saros Fault Zone both extending along the Gulf of Saros. The most important evidences of this movement are the left- and right-oriented shear deformations, which are correlated with structural elements, observed on the land and on the high-resolution shallow seismic records at the sea. Another important line of evidence supporting the evolution of this deformation is that the transgression started in the early-Late Miocene and turned, as a result of regional uplift, into a regression on the Gelibolu Peninsula during the Turolian and in the north of the Saros Trough during the Early Pliocene. The deformation on the Gelibolu Peninsula continued effectively until the Pleistocene. Taking into account the fact that this deformation affected the Late Pleistocene units of the Marmara Formation, the graben formation of the Gulf of Saros is interpreted as a Recent event. However, at least a small amount of compression on the Gelibolu Peninsula is observed. It is also evident that compression ceased at the northern shelf area of the Gulf of Saros.

Kinematics and evolution of the northern branch of the North Anatolian Fault (Ganos Fault) between the Sea of Marmara and the Gulf of Saros

Abstract The WSW–ENE-trending Ganos Fault is a dextral strike-slip fault running parallel to and southwest of the West Marmara Trough and south of the Saros Trough. Dextral structures started evolving in the early Miocene, and at this time the Ganos fault system developed from a part of the Thrace–Eskisehir fault system. Beginning in the late Pliocene (∼3.5 Ma), the North Anatolian transform fault propagated into the Marmara region and captured the Ganos Fault. Subsequently, this fault has accommodated the westward movement of the Anatolian Block. Because of the curvature of the microplate boundary in this area, the Ganos fault system has tended to rotate counterclockwise. Farther west in the Gulf of Saros, the strike-slip motion was accommodated by a new fault on the northern margin of the gulf, rather than along the northern coast of the Gelibolu Peninsula as previously thought. This interpretation differs from previous assessments of the position of the northern strand of the North Anatolian fault (Marmara segment) in the Marmara Sea and in the Gulf of Saros. The role of the Ganos Fault proposed in this paper is considerably different from that proposed by earlier studies. While the revised orientation of the North Anatolian fault on land is about 7° different than specified by previous authors, at sea it is different by ∼32° counterclockwise and ∼23° clockwise in the West Marmara and Saros submarine depressions, respectively. The revised position of the Ganos Fault in the Marmara Sea, derived from shallow and conventional seismic reflection data, calls into question the validity of evolutionary models previously used in kinematic and stress-failure analyses. In particular, it is not possible to regard the Marmara Sea as a pull-apart basin and the Gulf of Saros as a transtensional half-graben. Furthermore, palinspastic maps taking into account the revised position of the Ganos Fault and GPS slip vectors support the idea that a dextral master fault is present to the north of the Saros Trough with a sinistral oblique fault dominated by normal offset (Gelibolu Fault) to its south. The Gelibolu Fault is reactivated in a limited region.

The Tsunami of August 17, 1999 in Izmit Bay, Turkey

The Kocaeli 1999 Earthquake with an Mw = 7.4 caused major hazards throughout the NW of Turkey from Tekirdag to Bolu. Historical data indicates that some of the earthquakes around Izmit Bay have caused tsunamis. In this study, tsunami research for the Kocaeli 1999 Earthquake has been made also taking into consideration historical data. In this research more than about 70 data at 35 localities have been used to determine the tsunami evidences in the bay. Coastal observations indicated runups which were ranging from 1 to 2.5 m along the shores. However, the wave runups are more complex along the south coast due to the presence of coastal landslides (Değirmendere, Halidere, Ulasli, Karamürsel) and subsided areas (Kavakli to Yeniköy) along the shore. West of Yalova, evidence of tsunami rapidly diminished. In addition, possible tectonic mechanism has been determined by using 33 single-channel high-resolution digital seismic reflection profiles which were acquired following the Kocaeli 1999 Earthquake. As a result it has been determined that the Kocaeli Earthquake has created tsunami in Izmit Bay.

Evolution of the middle strand of North Anatolian Fault and shallow seismic investigation of the southeastern Marmara Sea (Gemlik Bay)

Abstract The Gemlik Bay is developed as a pull-apart basin during the late Pliocene-early Pleistocene mainly controlled by west-trending dextral strike-slip faults along the middle strand of the North Anatolian Fault zone, with the NW-trending Thrace-Eskisehir Fault playing secondary role. The North Anatolian Fault reached the eastern Marmara Sea ∼3.5 Ma ago, where its middle strand intersected the Thrace-Eskisehir Fault. GPS slip vectors measured on the Armutlu and Mudanya blocks show a displacement of 7–8 km during the last 3.5 Ma. The middle strand of the North Anatolian Fault zone has lower tectonic activity than the northern strand. Because uplift of the southeast Marmara Sea region has been continuous since the late Pliocene, the presence of fluviatile, lacustrine and deltaic environments in the Gemlik pull-apart basin over the same period supports a lower lever of tectonic activity. The transgressive Marmara Formation was deposited on top of these fluvio-lacustrine deposits following the Mediterranean inundation at ∼600 ka via the Strait of Canakkale. The Gemlik basin was affected both by two major sea-level falls at 160–132 and 24–11 ka, and minor short-lived sea-level variations, as a result of becoming a lacustrine setting five times since ∼600 ka. During these lowstands, stacked delta successions were deposited around the lake and on the transgressed shelves of the Marmara Sea.

Active tectonics of the İzmit Gulf (NE Marmara Sea): from high resolution seismic and multi-beam bathymetry data

Abstract Several active faults were determined in the Gulf of Izmit, using high-resolution shallow seismic and multi-beam bathymetry data. One of them is a buried fault (Fault 2), following central axis of the gulf, which forms the current morphology within its releasing and restraining bends. Releasing bends control the current morphology of the sub-basins. Also restraining bends form folds in the central basin and a thrust in the western basin. A left step over between two strike-slip faults (Faults 2 and 11) creates a transpressional area. Therefore, Hersek and Catal deltas are uplifted. It is determined that Fault 2 could not be related to the origination of the gulf because it cuts all basins and ridges, thus, present geometry of the Fault 2 is not suitable for the initial formation of the gulf. From this point of view, the Fault 2 is initiated recently compared to the whole North Anatolian Fault Zone (NAFZ) in the Marmara Sea. Therefore, Fault 2 is recognised as a new rupture of the NAFZ probably active since the end of the last glacial ice period.

Şarköy-Mürefte 1912 Earthquake's Tsunami, extension of the associated faulting in the Marmara Sea, Turkey

The historical tsunamis in the Marmara Seawere mainly caused by earthquakes andneeded to be documented. Following 1999Izmit earthquake occurred at the EasternMarmara region, a complete inventory ofactive faults in the Marmara Sea regionbecame much more stressed. To the west, thelatest event is 09.08.1912Şarköy-Mürefte Earthquake. Itoccurred on the active Ganos Fault zone andwas one of the largest earthquakes in theBalkans. The eastern termination of theassociated faulting is in the deep WestMarmara Trough, westernmost of thesuccessive basins forming the Marmara Sea.On the basis of recent multibeam bathymetryand seismic reflection data, estimatedtotal length of the surface rupture isabout 56 km. The historical data reviewedfrom library and archive documents,geological field surveys and offshoregeophysical investigations have shown thatthe 1912 earthquake produced a tsunami. Inaddition a seabed dislocation, the sourceof 1912 tsunami can also be assigned to thesediment slumps appearing in the form ofechelon landslide prisms along the southernslopes of the West Marmara Trough.

An assessment of trace element contamination in the freshwater sediments of Lake Iznik (NW Turkey)

Iznik Lake, a freshwater lake surrounded by a fertile basin of land in NW Turkey, is deteriorating gradually depending upon the increment in loadings which is ascribed to the inputs from streams, agriculture, excessive irrigation, urbanization and industrial activities along the shore, and atmospheric deposition. The main scope of this study is to assess the content, distribution and ecological risk of the elements (Al, Fe, Mn, V, Cd, Co, Cr, Cu, Ni, Pb, As and Zn) in the surficial sediments collected from 25 sites in the Lake Iznik. Quantitative indices and sediment quality guidelines were used to evaluate the pollution status of metals. The resulting estimates reflected a natural environment of low to moderate degree of impaction, and an approximate contribution of geogenic and anthropogenic inputs, with some variations among the stations. The enriched concentrations of As and Mn could be depending on the thermogenic activity along the active faults bounding the lake. Multivariate analysis demonstrated that the sources of Al, Fe, Co, Cr, Zn and V, concentrated at near-shore stations, could be attributed to mixed (lithogenic/anthropogenic) sources via streams. The enriched concentrations of Cd, Cu, Ni and Pb observed at the deep stations, and their sources were attributed to the transported/deposited sediments and partly atmospheric deposition. Except Ni, the metal concentrations in the majority of sediment samples were believed to be safe for living organisms. Local governments must prepare rational environmental strategies and suitable drainage programs to decrease the level of contaminants that pollute the environment and to prevent the dramatic drop of the lake’s water.

Tectonic setting of the southern Marmara Sea region: based on seismic reflection data and gravity modelling

Abstract On the basis of gravity modelling on the southern Marmara Sea shelf and conventional multichannel seismic reflection data, the tectonic setting of the region was studied. The relation of the middle strand of the North Anatolian Fault Zone with the Thrace–Eskisehir Fault Zone was examined. The southern Marmara Sea region was tectonically uplifted in the Late Pliocene. Gemlik Bay was developed during Late Pliocene–Early Pleistocene under the control of right lateral strike–slip faults along the middle strand of the North Anatolian Fault. The northwest trending Thrace–Eskisehir Fault is the second important tectonic element in this evolution.

New approaches in assessment of tsunami deposits in Dalaman (SW Turkey)

Some earthquakes in the Eastern Mediterranean are tsunamigenic, and some of their tsunamis affected the coastal area of the Gulf of Fethiye, SW Turkey. Recent trenching surveys on the low-lying coastal areas of Dalaman delta beach across the Rhodes Pass revealed three probable tsunami impacts as a result of the historical earthquakes of 1303, 1481, and 1741. Yet there have been relatively few studies of the processes associated with tsunami sediment transport, their deposition, and nature in geological record. In addition to the interpretation of sedimentary features, accurate palaeo-environmental assessments might be possible by distinctive biogeochemical researches on marine-sourced organic matters, geochemical properties, quantitative amounts of marine biomarkers, and deterministic ratios. The identification of major lipid biomarkers (fatty acids and sterols) in the samples recovered from the sidewalls of the studied trench, for example, indicated biogenic contributions due to the presence of phytoplankton, zooplankton, bacteria, and dinoflagellates. Quantitative estimation of biomarkers and deterministic ratios also indicated some evidences for marine-sourced organic matters, implying that biomarkers can be used to answer the open questions in tsunami and palaeo-tsunami researches.