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The North Anatolian Fault Zone (NAFZ) is the most prominent active fault system in Northwestern Turkey. It is a major fracture that traverses the Northern part of Asia Minor and marks the boundary between the Anatolian tectonic plate and the larger Eurasian continental block, and has been the source of numerous large earthquakes throughout history. The NAFZ splits into three strands at the eastern part of the Marmara Sea. The northern strand passes through Izmit Bay, traverses the Marmara Sea and reaches to the Saros Gulf. The central fault zone passes through Izmit Bay, traverses the Sea of Marmara and reaches the Saros Gulf to the southeast. Earthquakes on this zone involve primarily horizontal ground motions (strike-slip type of faulting). Because of this unstable tectonic system, the area is considered to be as one of the most seismically active zones of the world. In the last hundred years, numerous large earthquakes have also occurred along the NAFZ, in the western part of Turkey. Beginning with an earthquake in 1939, several more quakes - with Richter magnitudes greater than 6.7 - struck in progression along adjacent segments of the great fault. The August 17, 1999 Izmit earthquake was the eleventh of such a series that have broken segments of the NAFZ, in both eastward and westward direction. The epicenter of the 1999 earthquake was near Izmit, as well as the location of previous events. The sequence of historic events indicates that the next destructive tsunamigenic earthquake could occur west of the 1999 event in the Sea of Marmara. The present study incorporates the results of a subsequent 2001 study which uses standardized remote sensing techniques and GIS-methods – based on Digital Elevation Model (DEM) data, and on geo- morph metric parameters that influenced local site conditions in the Sea of Marmara, as determined with Digital elevation data of the Shuttle Radar Topography Mission (SRTM), and with high resolution ASTER-data. With such remote sensing methods, areas that are potentially vulnerable areas in the Sea of Marmara were detected, so that disaster mitigation strategies can be implemented more effectively in the future. Based on such technology, local site conditions, which exacerbated earthquake intensities and collateral disaster destruction in the Marmara Sea region, were identified. Also reviewed by the present study are the similarities of NAFZ with the San Andreas fault in California in the USA, for the formation of an active transform boundary of the strike-slip type, with the two sides moving horizontally and continuously past each other. Finally examined is the tectonic and continuing geodynamic evolution and collision between the Arabian Plate and Eurasia, which places in danger many cities in southeastern Turkey and NorthWest Syria - which is are located on the boundary with the Arabian tectonic plate, as evidenced by the recent disastrous earthquake of 8 February 2023 along the Eastern Anatolian Fault Zone (EAFZ).

The North Anatolian Fault Zone (NAFZ) is the most prominent active fault system in Northwestern Turkey. It is a major fracture that traverses the Northern part of Asia Minor and marks the boundary between the Anatolian tectonic plate and the larger Eurasian continental block, and has been the source of numerous large earthquakes throughout history. The NAFZ splits into three strands at the eastern part of the Marmara Sea. The northern strand passes through Izmit Bay, traverses the Marmara Sea and reaches to the Saros Gulf. The central fault zone passes through Izmit Bay, traverses the Sea of Marmara and reaches the Saros Gulf to the southeast. Earthquakes on this zone involve primarily horizontal ground motions (strike-slip type of faulting). Because of this unstable tectonic system, the area is considered to be as one of the most seismically active zones of the world. In the last hundred years, numerous large earthquakes have also occurred along the NAFZ, in the western part of Turkey. Beginning with an earthquake in 1939, several more quakes - with Richter magnitudes greater than 6.7 - struck in progression along adjacent segments of the great fault. The August 17, 1999 Izmit earthquake was the eleventh of such a series that have broken segments of the NAFZ, in both eastward and westward direction. The epicenter of the 1999 earthquake was near Izmit, as well as the location of previous events. The sequence of historic events indicates that the next destructive tsunamigenic earthquake could occur west of the 1999 event in the Sea of Marmara. The present study incorporates the results of a subsequent 2001 study which uses standardized remote sensing techniques and GIS-methods - based on Digital Elevation Model (DEM) data, and on geomorph metric parameters that influenced local site conditions in the Sea of Marmara, as determined with Digital elevation data of the Shuttle Radar Topography Mission (SRTM), and with high resolution ASTER-data. With such remote sensing methods, areas that are potentially vulnerable areas in the Sea of Marmara were detected, so that disaster mitigation strategies can be implemented more effectively in the future. Based on such technology, local site conditions, which exacerbated earthquake intensities and collateral disaster destruction in the Marmara Sea region, were identified. Also reviewed by the present study are the similarities of NAFZ with the San Andreas fault in California in the USA, for the formation of an active transform boundary of the strike-slip type, with the two sides moving horizontally and continuously past each other. Finally examined is the tectonic and continuing geodynamic evolution and collision between the Arabian Plate and Eurasia, which places in danger many cities in southeastern Turkey and NorthWest Syria - which is are located on the boundary with the Arabian tectonic plate, as evidenced by the recent disastrous earthquake of 8 February 2023 along the Eastern Anatolian Fault Zone (EAFZ). [ABSTRACT FROM AUTHOR]

Using geochemical and sedimentological properties of a sediment core IK2 from the 210 m deep Karamürsel Basin of the İzmit Gulf, temporal evolution of pollution and sources of trace elements (As, Co, Cr, Cu, Hg, Pb and Zn) were investigated. The core sequence extends back to AD865 and includes four mass-flow units (THU-1 to THU-4 from top to base) that were triggered by major earthquakes of AD 1999, 1509, 1206 and 865. The vertical profiles of elements and total organic carbon (TOC) in core IK2 display the highest enrichments in THU-1 that was triggered by the 1999 İzmit earthquake (Mw 7.4). The profiles also display massive erosion of sediments below THU-1, belonging to the industrial period. Principal component analysis (PCA) of geochemical data from core IK2 showed three clusters: (1) PC1 (Co, Cu, Zn, Hg, TOC); (2) PC2 (As, Cr); (3) PC3 (Al). Enrichment of PC1 elements in THU-1 indicates that the unit represents the contaminated surficial sediments remobilized mainly from the relatively steep slopes of the Karamürsel Basin by the earthquake shaking. Strong correlation between TOC and Cu, Zn, Hg, Co suggests additional contamination sources, such as the seepages from the disrupted industrial pipelines, oil refinery and storage tanks, following the earthquake. Moderate enrichment in Pb, and As severe enrichment in Zn and very severe enrichment in Hg in the THU-1 sediments occurred in the last century, but significantly magnified by the devastating 1999 İzmit earthquake and early diagenetic processes. [ABSTRACT FROM AUTHOR]

A devastating earthquake (Mw 7.4) struck near Izmit city, northwestern Turkey, on 17 August 1999. The relatively large size of this earthquake and site amplification conditions caused severe damage in the Marmara region as well as the city of Istanbul. The disastrous outcome of this large earthquake requires careful analysis of the seismic hazard including local site effects in this region. Therefore, the present work addresses the issue of local site effects and modelling of strong ground motion for this earthquake. We have estimated the soil effects using the horizontal-to-vertical (H/V) ratio. Furthermore, high-frequency records are simulated using a modified semi-empirical technique (MSET) by including estimated site effects. This modification will provide more reliable and precise simulated strong motion records. In the present study, strong ground motions are simulated at nine seismic stations in the epicentral range of 40–99 km. These stations were selected based on their recorded data quality. To validate the technique, we have compared the synthetic records with the observed records in terms of root mean square error (RMSE). This comparison includes time records, pseudo-acceleration spectra, mean period and predominant period. This comparison shows MSET has successfully simulated the 1999 Izmit earthquake. [ABSTRACT FROM AUTHOR]

Abstract The Sapanca-Akyazı segment (SAS) is located on western part of the North Anatolian Fault (NAF) of Turkey. It was ruptured together with four other segments during the 17th August 1999 İzmit earthquake (M w = 7.4) which caused ~145-km-long surface rupture in the east Marmara region. We conducted geomorphological investigations and 2D–3D paleoseismic trenching at 3 different sites near the Sakarya River along the SAS to obtain new data for the timing of past earthquakes and slip rate of this section of the NAF. Detailed investigations using Ground Penetrating Radar on the western bank of the Sakarya River reveal 18.5 ± 0.5 m of right-lateral cumulative offset of an alluvial terrace dated as 850 ± 11 years BP using Optically Stimulated Luminescence. The analysis of trench data from the three different sites of the SAS indicates the occurrence of four surface rupturing past earthquakes including the 1999 İzmit earthquake. According to the radiocarbon dating, these paleo-earthquakes can be correlated with the 1719 CE, 1567 CE, and 1037 CE historical earthquakes and suggest an average recurrence period between 273 and 322 years. The total dextral offset, the age of trench units and the terrace deposits together suggest a 22 ± 3 mm/yr slip rate for this portion of the NAF. Highlights • First geologic slip-rate estimated on the Sapanca-Akyazı segment of the NAF • First paleoseismologic data on the Sapanca-Akyazı segment of the NAF • Inter-event time between faulting events on the Sapanca-Akyazı segment of the NAF [ABSTRACT FROM AUTHOR]

The destructive earthquake that struck near the Gulf of Izmit along the North Anatolian fault in Northwest Turkey on August 17, 1999, not only generated a local tsunami that was destructive at Golcuk and other coastal cities in the eastern portion of the enclosed Sea of Marmara, but was also responsible for extensive damage from collateral hazards such as subsidence, landslides, ground liquefaction, soil amplifications, compaction and underwater slumping of unconsolidated sediments. This disaster brought attention in the need to identify in this highly populated region, local conditions that enhance earthquake intensities, tsunami run-up and other collateral disaster impacts. The focus of the present study is to illustrate briefly how standardized remote sensing techniques and GIS-methods can help detect areas that are potentially vulnerable, so that disaster mitigation strategies can be implemented more effectively. Apparently, local site conditions exacerbate earthquake intensities and collateral disaster destruction in the Marmara Sea region. However, using remote sensing data, the causal factors can be determined systematically. With proper evaluation of satellite imageries and digital topographic data, specific geomorphologic/topographic settings that enhance disaster impacts can be identified. With a systematic GIS approach - based on Digital Elevation Model (DEM) data - geomorphometric parameters that influence the local site conditions can be determined. Digital elevation data, such as SRTM (Shuttle Radar Topography Mission, with 90m spatial resolution) and ASTER-data with 30m resolution, interpolated up to 15 m) is readily available. Areas with the steepest slopes can be identified from slope gradient maps. Areas with highest curvatures susceptible to landslides can be identified from curvature maps. Coastal areas below the 10 m elevation susceptible to tsunami inundation can be clearly delineated. Height level maps can also help locate topographic depressions, filled with recently formed sediments, which are often linked with higher groundwater tables. Such areas are particularly susceptible to higher earthquake intensities and damage. The sum of risk GIS factors increases the susceptibility of local soils in amplifying seismic ground motions. Areas most susceptible to higher earthquake impacts can be identified using a systematic GIS approach, the weighted–overlay-method implemented in ArcGIS. Finally, the data obtained by remote sensing can be converted into Google Earth-kml-format and become available at no cost, to raise public disaster awareness and preparedness in the Sea of Marmara region.

We show the results of application of Differential SAR Interferometry to the MW 7.4, August 17, 1999, Izmit earthquake, Western Turkey. The differential interferogram is obtained using an interferometric ERS2 ascending pair with a time interval of 35 days (August 13th - September 17th). The fringe pattern clearly defines the coseismic displacement field extended in an area of about 100 km N-S and 120 km E-W. The analysis of the interferogram shows the right-lateral strike-slip movement on the activated section of the North Anatolian fault system. The maximum SAR-detected displacement ranges between 117.6 cm and 134.4 cm in the proximity of Gölcük. We invert SAR data for uniform dislocation on a single fault plane using a Montecarlo procedure, with the aim of testing a large set of a priori possible asperity distributions on the fault. We then use a forward modeling approach to evaluate the slip variability for the dislocation using additional constraints as surface offsets and seismicity distribution: in this case we allow unit cells to undergo different values of slip in order to refine the initial dislocation model. Misfits between SAR data and modeled slant range displacements are generally low for all our models (~ 12 cm). Our results indicate that slip is concentrated in the central-western part of the fault, in the upper 10-15 km, tapering to the fault tips. For the Izmit case, we note that a well constrained fault model can be obtained only integrating DInSAR data with additional observations. This is mainly due to an undersampling of the displacement field by DInSAR, caused by decorrelation and lack of image data.

A linear finite-fault inversion procedure is applied to teleseismically recorded broadband P and SH velocity waveforms of the August 17, 1999, İzmit earthquake, to derive spatial and temporal distributions of the co-seismic slip over the representative three-segment model fault. The model fault is longer than the mapped surface rupture, and it extends offshore for 25 km in the west, to define the western end of the earthquake rupture. The teleseismically derived slip model suggests a bilateral rupture with a total seismic moment release of 2.6 ×1020 Nm, and that the rupture was dominated by failure of two major asperities with peak slip amplitudes reaching 7 m. The hypocentral area was represented by the relatively low displacement that separated the large asperities. In the west, the rupture reached the eastern entrance of the Çınarcık basin beneath the Sea of Marmara, with an average slip of ca. 2 m. This indicates that the rupture propagated offshore for ca. 20 km after crossing Hersek Peninsula. The analysis also reveals that the total rupture process time was 32 s, while the main seismic moment release, which corresponded to the rupture of the two large asperities, occurred between 4 s and 16 s after rupture initiation. The strong wave energy arrivals from the failure of the large asperities were preceded by weak wave arrivals in the initial section of the teleseismic waveforms used in this study. Along with some observations from previous studies, this emergent onset of the wave arrivals prompts us to discuss the possibility of a seismic nucleation process for this earthquake.

The Karadere segment of the North Anatolian Fault (NAF) is the easternmost part that ruptured during the 17 August 1999 ጏzmit earthquake (Mw 7.4). It has a different orientation, at N65°E to other segments which have a nearly E-W trend, and lesser dextral displacement, with maximum 2.3 m in contrast with 5.2 m in the ruptured neighbouring western segment. Two palaeoseismological trenches, at Kazimiye and Karadere sites, were excavated on the central part of the Karadere segment to determine the timing of past earthquakes. Excavation of the Kazimiye site revealed the occurrence of five past events since the 4th century A.D., including the 1999 ጏzmit earthquake. The oldest event occurred after A.D. 231-407 and before A.D. 420-584 based on 14 C dating results. This event may correspond to either the A.D. 358 earthquake or the A.D. 554 historical earthquake. The younger three events predate 1999 and postdate A.D. 420-584. At the Karadere trench site, three past events, including the 1999 İzmit earthquake, were identified. The penultimate event was observed on the trench wall and dated to be after A.D. 1298-1370. The older event is dated as before A.D. 1150-1261, which may correspond to one of the determined events in the Kazimiye trench. In summary, palaeoseismological data provide evidence for at least five large earthquakes on the Karadere segment since A.D. 231-407, including the 1999 İzmit earthquake. [ABSTRACT FROM AUTHOR]

The Mw 7.4, August 17, 1999 İzmit earthquake ruptured a ~100-km-long onshore section of the North Anatolian Fault (NAF) in the eastern Marmara region, causing the loss of more than 20,000 people and extensive destruction. The western termination and total length of the earthquake rupture is still a matter of debate because the surface rupture goes of shore in the Gulf of İzmit after displaying a coseismic displacement of ~5 m. Such a considerable slip implies that the fault rupture must definitely continue some distance westward on the sea floor, but where exactly it terminated is difficult to determine. h is issue is critical for determining the size of the Marmara seismic gap, south of Istanbul. Therefore, to explore the fault scarps associated with the 1999 rupture on the sea floor, we have studied ultra-high resolution bathymetry (0.5 m resolution) acquired with a remotely operated submersible during the MARMARASCARPS cruise, an innovative approach which proved to be useful in seeking earthquake surface deformation on the sea floor. The analysis of microbathymetry suggests that the 1999 İzmit earthquake rupture extended westward at least to 29.38°E longitude about 10 km west of the Hersek Delta in the Gulf of İzmit. It is clearly expressed as a sharp fault break with a 50 cm apparent throw across the bottom of a submarine canyon. Further west, a pronounced and linear fault rupture zone was observed, along with fresh enéchelon cumulative fault scarps. We infer that the seismic break continues westwards, reaching a total length of ~145 km at around 29.24°E longitude, consistent with the 1999 rupture deduced from SAR interferometry. It appears to stop at the entrance of the Çinarcik Basin where a normal faulting component prevails. We suggest that fault complexity at the junction between dominant strike-slip faulting along the Izmit fault and signii cant normal faulting in the Çinarcik Basin may act as a barrier to rupture propagation of large earthquakes. [ABSTRACT FROM AUTHOR]

The destructive earthquake that struck near the Gulf of Izmit along the North Anatolian fault in Northwest Turkey on August 17, 1999, not only generated a local tsunami that was destructive at Golcuk and other coastal cities in the eastern portion of the enclosed Sea of Marmara, but was also responsible for extensive damage from collateral hazards such as subsidence, landslides, ground liquefaction, soil amplifications, compaction and underwater slumping of unconsolidated sediments. This disaster brought attention in the need to identify in this highly populated region, local conditions that enhance earthquake intensities, tsunami run-up and other collateral disaster impacts. The focus of the present study is to illustrate briefly how standardized remote sensing techniques and GIS-methods can help detect areas that are potentially vulnerable, so that disaster mitigation strategies can be implemented more effectively. Apparently, local site conditions exacerbate earthquake intensities and collateral disaster destruction in the Marmara Sea region. However, using remote sensing data, the causal factors can be determined systematically. With proper evaluation of satellite imageries and digital topographic data, specific geomorphologic/topographic settings that enhance disaster impacts can be identified. With a systematic GIS approach - based on Digital Elevation Model (DEM) data - geomorphometric parameters that influence the local site conditions can be determined. Digital elevation data, such as SRTM (Shuttle Radar Topography Mission, with 90m spatial resolution) and ASTER-data with 30m resolution, interpolated up to 15 m) is readily available. Areas with thesteepest slopes can be identified from slope gradient maps. Areas with highest curvatures susceptible to landslides can be identified from curvature maps. Coastal areas below the 10 m elevation susceptible to tsunami inundation can be clearly delineated. Height level maps can also help locate topographic depressions, filled with recently formed sediments, which are often linked with higher groundwater tables. Such areas are particularly susceptible to higher earthquake intensities and damage. The sum of risk GIS factors increases the susceptibility of local soils in amplifying seismic ground motions. Areas most susceptible to higher earthquake impacts can be identified using a systematic GIS approach, the weighted-overlay method implemented in ArcGIS. Finally, the data obtained by remote sensing can be converted into Google Earth-kml-format and become available at no cost, to raise public disaster awareness and preparedness in the Sea of Marmara region. [ABSTRACT FROM AUTHOR]

The North Anatolian Fault (NAF) is one of the most destructive fault zones of the world and it lies throughout the northern Turkey with 1500 km length nearly in east-west trending arc shape. It is almost totally broken with large earthquakes during 20th century except two main seismic gaps: Yedisu seismic gap in the east and Marmara seismic gap in the west. The last destructive earthquakes occurred in the eastern Marmara region in 17 August and 12 November 1999 and 150 km and 50 km sections of the NAF were ruptured between Yalova and Düzce respectively. North Anatolian Fault has a relatively narrow deformation zone between Erzincan and Bolu, but it bifurcates to the west of Bolu and separates different main tectonic and morphological units from each other in the eastern Marmara Region. These units are; Istanbul-Zonguldak Zone (or Kocaeli peneplain in morphotectonic manner), Armutlu-Almacik Zone (Armutlu-Almacik High or Samanli Mountains in morphotectonic manner) and Sakarya Continent (or Bursa-Bilecik relief in morphotectonic manner). Between the Gulf of Izmit and the Sapanca Lake the NAF follows an elongated depression and constitutes the boundary between Kocaeli peneplain and the Samanli Mountains. The 17 August 1999 earthquake ruptured five segments on NAF between Yalova and Gölyaka (Düzce). These segments are named as Yalova, Karamürsel-Gölcük, Izmit- Sapanca Lake, Sapanca-Akyazi and Karadere from west to east. The surface rupture of 1999 Izmit earthquake between the Gulf of Izmit and the Sapanca Lake, the Izmit-Sapanca Lake segment, has mainly followed this elongated depressional morphology. The morphologic features, observed along the surface rupture, indicate that the surface rupture of 1999 Izmit earthquake was also followed by past earthquakes. These features are elongated ridges, offset streams and hills, sag ponds and depressional areas. In the eastern part of the Gulf of Izmit, in the southwestern part of Kullar village, Yaylacik Hill is offset as 420 m by the fault. The measured offset of the river next to the Yaylacik Hill is 380 m in minimum and 450 m in maximum. To the east, Sarimese Hill, on the south of Sarimese village, is mapped as an elongated ridge. The right step-overs on the west and east of Tepetarla village are represented by depressional swampy areas. To the eastwards, around Acisu village, the deflected streams and the sag ponds are the results of long-term activity of the NAF in the region. The comparison of the measured offset along the segment and the slip rates derived from recent GPS measurements reveals that the NAF has been active along the same traces at least since 20.000 years on Izmit-Sapanca Lake segment. In order to determine the past earthquakes that ruptured the segment, a trench is excavated on the eastern part of the Izmit-Sapanca Lake segment, east side of Acisu village, where the surface rupture follows the northern slope of an east-west trending ridge. On the trench site, 1999 Izmit earthquake surface rupture trends N85°E direction as two branches and limits a depressed area which is located on the easternmost part of the site. The trench, with a length of 21 m and a maximum depth of 2,5 m, is excavated perpendicular to these two branches of the surface rupture. The stratigraphy of the trench is dominated by clay layers which have different physical properties. According to the stratigraphical and structural relationships three past event horizons are mapped in the trench. The event horizons are dated with radiocarbon dating (C14) of two charcoal samples. The youngest event horizon (ACSP-1) is before A.D.1300 and should represent an earthquake which happened around A.D.1000's. … [ABSTRACT FROM AUTHOR]

Abstract: On August 17, 1999, a major earthquake (M w=7.4) occurred, affecting a large area in northwestern Turkey. A 150-km-long section of the North Anatolian Fault ruptured from the entrance of the Gulf of İzmit to Gölyaka in the east during the earthquake. We utilized high-resolution shallow seismic data acquired during a post-earthquake cruise to find evidence of gas seeps, gas-charged sediments, and sediment failure in the Eastern (İzmit) Basin of the Gulf of İzmit. The data showed anomalies that suggest the presence of increased gas in the gulf after the earthquake. Five major zones of offshore mass movement were found in the study area. Comparison of data collected before and after the earthquake indicates that the apparent amount of gas increased after the earthquake and the mass movement has a causative relationship to the August 17, 1999 earthquake. Therefore, we conclude that the seismic event, presence of increased gas, and the offshore mass movements in the study area are interrelated. [Copyright &y& Elsevier]