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The 1500km long, EW directional North Anatolian Fault Zone (NAFZ), and the 700km long, SSW directional East Anatolian Fault Zone (EAFZ) are the major geophysical features in Turkey. They are formed where the Eurasian, Anatolian, and Arabian plates meet. Both faults have produced devastating earthquakes (M>6) throughout history and are still actively deforming and threatening populous areas. Even though individual studies focus on the NAFZ and EAFZ, none of them offer a method for continuous monitoring. In this study, we are taking advantage of the Interferometric Synthetic Aperture Radar (InSAR) method and adopting the Small BAseline Subset (SBAS) time series approach to map deformation over large swaths (hundreds of km). We developed a web-based, automated system that takes publicly available Sentinel-1 SAR images and generates deformation maps. We chose the Elazig region as our pilot study area because of the destructive M6.7 earthquake that occurred in January 2020. Our initial results capture the co-seismic deformation coherently and also provide insights into pre-seismic and post-seismic deformation characteristics. Our goal is to provide the scientific community with accurate and easy-to-interpret deformation maps, without needing advanced remote sensing knowledge.

SUMMARY The offshore part of the North Anatolian Fault (NAF) beneath the Marmara Sea is a well-known seismic gap for future M > 7 earthquakes in the sense that more than 250 yr have passed since the last major earthquake in the Central Marmara region. Although many studies discussed the seismic potential for the future large earthquake in this region on the basis of historical record, geodetic and geological observations, it is difficult to evaluate the actual situation on the seismic activity and structure along the NAF beneath the Marmara Sea due to the lack of ocean bottom seismic observations. Using ocean bottom seismometer observations, an assessment of the location of possible asperities that could host an expected large earthquake is undertaken based on heterogeneities in the microseismicity distribution and seismic velocity structure. Specifically, seismic tomography and precise hypocentre estimations are conducted using offshore seismic data whose recording period is 11 months. About five times more microearthquakes are detected with respect to events recorded in a land-based catalogue. A comparison with previously published results from offshore observation data suggests that the seismicity pattern had not changed from 2014 September to 2017 May. The location accuracy of microearthquakes is greatly improved from only the land-based earthquake catalogue, particularly for depth direction. There are several aseismic and inactive zones of microearthquake, and the largest one is detected using land-based seismic observation, whereas other zones are newly detected via offshore observations. The obtained velocity model shows a strong lateral contrast, with two changing points. The western changing point corresponds to a segmentation boundary, where the dip angle of the NAF segments changed. High-velocity zones from tomographic images are characterized by low seismicity eastward of the segment boundary. To the east of 28.50°E, the high-velocity zone becomes thicker in the depth direction and is characterized by low seismicity. Although the low seismic activity alone could be interpreted as both strong coupling and fully creeping, the high-velocity features at the same can be concluded that these zones are consist of brittle material and strong coupling. From comparison with other geodetic and seismic studies, we interpret these zones as locked zones that had been ruptured by the past large earthquakes and could be ruptured by future ones. These zones might accumulate strain since the main shock rupture associated with the 1766 May Ms 7.3 earthquake, the latest major earthquake in this region.

As the earliest institute in Turkey dedicated to locating, recording, and archiving earthquakes in the region, the Kandilli Observatory and Earthquake Research Institute (KOERI) has a long history in seismic observation, which dates back to the installation of its first seismometers soon after the devastating Istanbul earthquake of 10 July 1894. For over a century, since the deployment of its first seismometer, the KOERI seismic network has grown steadily in time. In this article, we present the KOERI seismic network facilities as a data center for the seismological community, providing data and services through the European Integrated Data Archive (EIDA) and the Rapid Raw Strong-Motion (RRSM) database, both integrated in the Observatories and Research Facilities for European Seismology (ORFEUS). The objective of this article is to provide an overview of the KOERI seismic services within ORFEUS and to introduce some of the procedures that allow to check the health of the seismic network and the quality of the data recorded at KOERI seismic stations, which are shared through EIDA and RRSM.

A submarine area close to the Turkish and Greek border between the cities of Samos-Greece and Seferihisar-Turkey has been shaked on October 30, 2020 by a Mw = 6.9 earthquake. In this study, the finite source mechanism of the Samos earthquake was investigated using geodetic methods and the coseismic behavior of the earthquake was modeled. The observed coseismic displacements at 62 sites were inverted for the fault geometry and the slips. The mainshock did not generate an on-land surface rupture. However, the uniform slip modeling shows a finite source of 43.1 km long and 16 km wide rupture, which slips 1.42 m along a north dipping normal fault extending from the Aegean Sea floor to a depth down to similar to 13 km. While the uniform slip model is consistent with the seismological solutions and provides a sufficient fit to the far field coseismic offsets, a distributed slip model is necessary to account for the near field coseismic displacements.

We analyzed GPS data to investigate the source parameters of the 2014 North Aegean earthquake (Mw 6.9). We simultaneously inverted strike, dip, rake, average slip, moment, size, and location of the mainshock rupture using coseismic displacements. We also investigated static stress change associated with the mainshock and its influence on aftershock activity. Previous solutions of focal mechanism showed that mainshock has a nearly pure strike-slip nature. Our results also indicate that the mainshock has a right lateral strike-slip mechanism with a substantial extensional component. Average coseismic slips are 48 cm and 25 cm on the horizontal and vertical axis, respectively. Coseismic displacements reach up to 51.35 ± 4.55 mm at ~60 km from the hypocenter (LEMN station). It appears that the mainshock ruptured a fault section approximately 28 km deep and 70 km long and generated a stress drop along the ruptured segment ranging between 3 and 10 bar, with a stress increase of 3 bar at the edges of the rupture. Aftershocks were distributed to a broader area as coseismic stress increase affected a 200-km-long section of the western North Anatolian Fault.

In the past 1500 years, seven sequences of significant earthquakes have occurred on a 160-km-long segment of the North Anatolian Fault zone (NAFZ) centered on Istanbul. The most recent of these sequences will be complete with the future occurrence of one or more Mw ≥ 7.0 earthquakes near the city. From a summation of the seismic moment released by historical earthquakes between 500 and 2000 CE we calculate a mean slip deficit rate of 9.9 mm/year. Our moment summation procedure sums the seismic moment associated with known historical earthquakes in the past 1500 years based on rupture length and assumed seismogenic depth. We observed that in the 1999 Izmit earthquake, strongly coupled fault patches were associated with the highest co-seismic slip. In our calculated map of present-day slip-potential, we recognize several such patches from their low present-day rate of microseismicity, e.g. segments beneath the Kumburgaz and Eastern (Cinarcik) Marmara Basins. In contrast, intervening weakly coupled patches host high present-day background seismicity, e.g. the segment beneath the Western (Tekirdag) Basin. This lends credibility to an interpretation of future earthquakes occurring in three seismogenic segments of the NAFZ corresponding to three deep basins in the Sea of Marmara. The present-day slip deficits reach up to 1.7 m beneath the Western (Tekirdag Basin) segment, and 4.0 m and 5.4 m beneath the Central (Central High and Kumburgaz Basin) and Eastern (Cinarcik Basin) segments, respectively. These segments most recently ruptured in August 1766, May 1766 and October 1509 and currently have a potential to generate Mw 7.2, Mw 7.4 and Mw 7.5, earthquakes respectively. Although contiguous ruptures have not occurred historically, ruptures of contiguous segments could occur as a Mw 7.5 earthquake in the west, or a Mw 7.6 earthquake in the east or as a single through-going Mw 7.7 rupture.

The cause of damage to the environment, forestfires have a significant role in order to give way to natural disasters in theworld. Forest fires not only affect ecosystems negatively, but also causeserious problems in economic and social life. As a result of forest fires thatoccurred between the years of 1937-2016 in Turkey 1,661,506 hectares of forestarea was burnt. It is sometimes difficult and impossible to collect data fromforests after forest fires. In addition, remote sensing techniques and algorithmsare frequently used in determining the burning areas considering the longduration and the cost will be high. Different satellite images (Landsat, MODIS,SPOT, etc.) in various properties are important data sets of remote sensingtechnology which is frequently used in recent years to map fire intensity, firedamage and burnt zones. In this study, forest fire that occurred and continued4 days in Seferihisar district of İzmir province on August 9, 2009 was analyzedby remote sensing techniques using Landsat 5 satellite images. Two Landsatimages acquired in July 2009 as pre fire and in August 2009 as post-fire. Inthis study, the capacity of Normalized Burn Ratio (NBR) and NormalizedDifference Vegetation Index (NDVI) indices and differenced Normalized DifferenceVegetation Index (dNDVI) derived from Landsat 5 images have been analyzed inorder to assess the fire severity. Besides NDVI and NBR indices results,maximum likelihood algorithm which is supervised classification method wasapplied to pre and post fire satellite images. The burnt area after forest firewas calculated as 711 ha with dNDVI, 695 ha with dNBR and 665 ha with maximumlikelihood algorithm of pixel based supervised classification method. Based onthe three different methods of results are compatible, rational and consistentwith the results of the General Directorate of Forestry., Çevreyeverdiği zararlar nedeni ile orman yangınları dünyada doğal afetler içindeönemli bir yere sahiptir. Orman yangınları sadece ekosistemleri olumsuzetkilemekle kalmayıp, aynı zamanda ekonomik ve sosyal yaşamda da ciddisorunlara neden olmaktadır. Türkiye’de 1937-2016 yılları arasında meydana gelenorman yangınları sonucu 1.661.506 hektarlık orman alanı yanarak tahripolmuştur. Orman yangınları sonrası araziden veri toplamak zaman zaman zor ve imkânsızolabilmektedir. Ayrıca yaşanan afet sonrası arazi çalışmaları uzun süreceği vemaliyetinin fazla olacağı göz önüne alınarak yanan alanların belirlenmesindegünümüzde uzaktan algılama teknolojilerine ve bu alanda kullanılan algoritmalarınasıklıkla başvurulmaktadır. Çeşitli özelliklere sahip farklı uydu görüntüleri(Landsat, MODIS, SPOT, vb.), yangın şiddetini, yangın hasarlarını ve yanmışbölgeleri haritalamak için son yıllarda sıklıkla kullanılan uzaktan algılamateknolojisinin önemli veri setleridir. Bu çalışmada 9 Ağustos 2009 tarihindeİzmir ili Seferihisar ilçesinde meydana gelen ve 4 gün süren orman yangını,Landsat 5 uydu görüntüleri kullanılarak uzaktan algılama teknikleri ile analizedilmiştir. Çalışma bölgesine ait orman yangını öncesi Temmuz 2009 ve ormanyangını sonrası Ağustos 2009 tarihli görüntüler alınarak Normalize EdilmişYanma Şiddeti (Normalized Burned Ratio-NBR) ve Normalize Edilmiş Vejetasyonİndeksi (Normalized Differenced Vegetation Index - NDVI) indeksleri ile buindekslerin farkları kullanılarak elde edilen Fark Normalize Edilmiş YanmaŞiddeti (Difference Normalized Burned Ratio-Dnbr) ve Fark Normalize EdilmişVejetasyon İndeksleri kullanılarak yanarak tahrip olmuş alanlar tespitedilmiştir. Veri setine ayrıca piksel tabanlı kontrollü sınıflandırmanınmaksimum benzerlik algoritması uygulanmıştır. Orman yangını sonrası yanaraktahrip olan alan dNDVI ile 711 ha, dNBR ile 695 ha, piksel tabanlı kontrollü sınıflandırmayönteminin maksimum benzerlik algoritması ile de 665 ha olarak hesaplanmıştır.Üç farklı yöntemin sonuçları Orman Genel Müdürlüğü sonuçları ile uyumlu vetutarlı olduğu sonucuna varılmıştır.

The offshore part of the North Anatolian Fault (NAF) beneath the Marmara Sea is a well-known seismic gap for future M > 7 earthquakes in the sense that more than 250 years have passed since the last major earthquake in the Central Marmara region. Here, an assessment on the location of possible asperities to host the expected next large earthquake is done based on the heterogeneities on the seismic velocity structure. Using long-term ocean bottom seismograph (OBS) observation data, seismic tomography and precise hypocenter estimations have been conducted. As a result, about five times more microearthquakes than the events in a land-based catalog has been detected. A comparison with previously published results suggests that the seismicity pattern has not changed during the three years period between Sep. 2014 and Jun. 2017. The obtained velocity model shows strong lateral contrast whose changing points locate at 28.10°E and 28.50°E. The western corner of the area (28.10°E) corresponds to a segmentation boundary where the dip angle of the NAF segments changed. The high velocity zones in the tomographic images are characterized by low seismicity eastward from the segment boundary at 28.10°E. Eastern 28.50°E, the high velocity zone becomes thicker in the depth direction. These zones are interpreted as asperities to be ruptured by the next large earthquake which are possibly accumulating strain since the mainshock rupture associated with the May 1766 Ms7.3 earthquake.

The survival of humanity is dependent on the survival of forests and the ecosystems they support, yet annually wildfires destroy millions of hectares of global forestry. Wildfires take place under specific conditions and in certain regions, which can be studied through appropriate techniques. A variety of statistical modeling methods have been assessed by researchers; however, ensemble modeling of wildfire susceptibility has not been undertaken. We hypothesize that ensemble modeling of wildfire susceptibility is better than a single modeling technique. This study models the occurrence of wildfire in the Brisbane Catchment of Australia, which is an annual event, using the index of entropy (IoE), evidential belief function (EBF), and logistic regression (LR) ensemble techniques. As a secondary goal of this research, the spatial distribution of the wildfire risk from different aspects such as urbanization and ecosystem was evaluated. The highest accuracy (88.51%) was achieved using the ensemble EBF and LR model. The outcomes of this study may be helpful to particular groups such as planners to avoid susceptible and risky regions in their planning; model builders to replace the traditional individual methods with ensemble algorithms; and geospatial users to enhance their knowledge of geographic information system (GIS) applications.

Strong ground motion records and free open access to strong‐motion data repositories are fundamental inputs to seismology, engineering seismology, soil dynamics, and earthquake engineering science and practice. This article presents the current status and outlook of the Observatories and Research Facilities for European Seismology (ORFEUS) coordinated strong‐motion seismology services, namely the rapid raw strong‐motion (RRSM) and the engineering strong‐motion (ESM) databases and associated web interfaces and webservices. We compare and discuss the role and use of these two systems using the Mw 6.5 Norcia (Central Italy) earthquake that occurred on 30 October 2016 as an example of a well‐recorded earthquake that triggered major interest in the seismological and earthquake engineering communities. The RRSM is a fully automated system for rapid dissemination of earthquake shaking information, whereas the ESM provides quality‐checked, manually processed waveforms and reviewed earthquake information. The RRSM uses only data from the European Integrated Waveform Data Archive, whereas the ESM also includes offline data from other sources, such as the ITalian ACcelerometric Archive (ITACA). Advanced software tools are also included in the ESM to allow users to process strong‐motion data and to select ground‐motion waveform sets for seismic structural analyses. The RRSM and ESM are complementary services designed for a variety of possible stakeholders, ranging from scientists to the educated general public. The RRSM and ESM are developed, organized, and reviewed by selected members of the seismological community in Europe, including strong‐motion data providers and expert users. Global access and usage of the data is encouraged. The ESM is presently the reference database for harmonized seismic hazard and risk studies in Europe. ORFEUS strong‐motion data are open, “Findable, Accessible, Interoperable, and Reusable,” and accompanied by licensing information. The users are encouraged to properly cite the data providers, using the digital object identifiers of the seismic networks. © 2021 Seismological Society of America ISSN:0895-0695 ISSN:1938-2057

The Aegean region is one of the most seismically active regions in Turkey and comprises the Hellenic Arc, Greece, and Western Turkey. The Tuzla Fault, which lies between the town of Menderes and Cape Doganbey, is one of the major seismic threats in western Turkey due to its seismic potential to generate a major earthquake (M 6, near Doganbey Cape in 1992) and proximity to the city of Izmir which sustained damage due to the earthquake that occurred in the Aegean Sea on October 30th, 2020. In order to estimate strain rates and seismic potential around the Tuzla Fault, five global positioning system (CPS) surveys were carried out between 2009 and 2012. Estimated GPS velocities in the study area exceed 20 mm/year, which is in line with previous studies. We use two different approaches to calculate the strain accumulation on and around the Tuzla Fault. The first method adopts forming triangles using the GPS sites as corners and calculating strain rates within those triangles. The second method adopts a bicubic interpolation approach described by Holt and Haines, 1993. Maximum values of strain accumulation were found to reach up to 200 nanostrain/year.

We investigated microseismicity, geodetic slip and structural setting along the western North Anatolian Fault (NAF) to characterize their influence on pre-, co- and post-seismic stages of the 2014 North Aegean Earthquake (M 6.9). We identified that the NAF in North Aegean Sea (NAS) operates beneath three basins and two transpressional ridges rather than a single through-going basin. Refined hypocenters indicate that NAF is a narrow shear-zone in the east, and systematically expands towards the west. Microseismicity has a wide spread epicentral pattern at pre-seismic stage of the 2014 earthquake, but later tightens during post-seismic stage. This suggests that pre-seismic strain accumulation was completed on the main fault and transferred to surrounding secondary structures, and the slip returned back to the main fault following the mainshock. Overall microseismicity pattern shows that seismogenic zone becomes deeper to the west and shallower to the east. Three fault segments merged with two step-overs have failed during the 2014 North Aegean Earthquake rupturing a ~90 km section of the NAF. The co-seismic slips reach ~90 cm beneath western step-over and remains below ~60 cm beneath eastern step-over. Along-fault pre- and co-seismic geodetic slips show a complementary pattern verifying that the 2014 mainshock generated the highest slip at pre-seismically locked patches, located beneath transpressive ridges hosting two step-overs. The existence of high pre-shock concentrations underneath suggests fracturing at seismogenic basement overcoming frictional strength at these two fault step-overs.

A tsunami warning system providing services in the Eastern Mediterranean, Aegean, Marmara and Black Seas under the UNESCO Intergovernmental Oceanographic Commission (IOC)—Intergovernmental Coordination Group (ICG) for the Tsunami Early Warning and Mitigation System in the North-Eastern Atlantic, the Mediterranean and Connected Seas (NEAMTWS) framework was established in Turkey by the Kandilli Observatory and Earthquake Research Institute (KOERI) (Özel et al., 2011). KOERI’s Regional Earthquake and Tsunami Monitoring Center (RETMC) was established on the foundations of the legacy KOERI National Earthquake Monitoring Center (NEMC) by adding observation, analysis and operational capability related to tsunami early warnings after an extensive preparatory period during 2009 and 2011. The center initiated its test-mode 7/24 operational status as a national tsunami warning center in 2011, and after a one year period it became operational as a candidate tsunami warning center for NEAMTWS on 1 July 2012, together with CENALT (Centre d’Alerte aux Tsunamis—France) and followed by the NOA (National Observatory of Athens—Greece) on 28 August 2012, INGV (Instituto Nazionale di Geofisica e Vulcanologia—Italy) on 1 October 2014 and IPMA (Instituto Português do Mar e da Atmosfera—Portugal) on 1 February 2018, completing full coverage of the tsunami-prone regions monitored by NEAMTWS. In this paper, an overview of the progress and continuous improvement of KOERI’s tsunami early warning system will be presented, together with lessons learned from important tsunamigenic events, such as the 20 July 2017 Bodrum–Kos Mw 6.6 and 30 October 2020 Samos–Izmir Mw 6.9 earthquakes. Gaps preventing the completion of an effective tsunami warning cycle and areas for future improvement are also addressed.

Coastal zones are in a state of continual flux worldwide, due in part to seasonal factors and in part to influences operating over longer periods of time. Discerning changes on different timescales remains a challenge. This study compares shoreline position and nearshore bathymetry over a time interval of 16 years in order to determine the extent of medium-term changes in comparison with short-term changes along the southwestern Black Sea coast of Turkey near Kilyos. For this purpose the results of surveys completed in 2001 and 2002 are compared with data collected in December 2015, September 2016, and March 2017 at the same location using a differential global positioning system (DGPS) in real-time kinematic (RTK) configuration combined with echo-sounder profiling. Average shoreline recession over the 16-year period (medium term) has been estimated at 3–4 cm/year as opposed to an average of 9.5 m in the 12-month period from June 2001 to June 2002 (short term). The medium-term nearshore sediment loss has been approx. 100–125 m3/m shoreline since the early 2000s. Over the same period a prominent offshore bar has moved seaward at a maximum rate of 1 m/year since 2002. Considering the large discrepancy in the shoreline recession rates recorded in the short and medium term, this aspect must be taken into account in any integrated coastal zone management strategy.

Since 1766, the North Anatolian Fault Zone in the Marmara Sea has not generated a Mw=7.0 earthquake. In the Marmara Sea, three different segments are located having ~25 mm slip rates and ~10 mm slip deficit per year. The faulting mechanism within the Marmara Sea has capability of generating earthquakes larger than Mw7.0. We are continuously monitoring this critical region with more than 30 seismo-geodetic stations equipped with 100 Hz sampling seismographs and 1 Hz sampling GPS receivers, in order to detect fast and slow tectonic motions in and around the Marmara Sea at temporal and spatial scale from milliseconds to years and from centimeters to tens of kilometers.The data obtained during this study provides us to identify the slip deficit along the fault, the segmentation of fault, the interaction between slip-deficit and background seismicity. Besides, these data also contribute to identify the pre-seismic seismo-geodetic behavior and co-seismic slip when Mw=7.0 type of earthquakes occurs.

Thanks to both technological evolution and analysis improvement in the past decades, space geodesy can now monitor crustal movements of a few millimeters over time opening new prospects for the study of earthquakes. However, fully exploiting the potential of geodetic measurements is subject to their further integration with seismological analysis and requires the development of a multidisciplinary approach. The new joint IAG-IASPEI sub-commission on Seismogeodesy aims to facilitate the cooperation between the geodetic and the seismological communities in order to improve our current understanding of the different processes leading to earthquakes. The new Seismogeodesy sub-commission will focus on both observational challenges and theoretical aspects. Particular effort will be dedicated to identifying gaps of knowledge and opportunity for progress. Specifically, the sub-commission will:* actively encourage the cooperation between all geoscientists studying the plate boundary deformation zones, by promoting the exploitation of synergies between different fields;* work to reinforce collocated and integrated geodetic and seismological monitoring of seismically active areas, inland and off-shore by increasing and/or developing infrastructures dedicated to broadband observations from the seismic wave band to the permanent displacement;* be a reference group for the integration of the most advanced geodetic and seismological techniques by developing consistent methodologies for data reduction, analysis, integration, and interpretation;* act as a forum for discussion and scientific support for international geoscientists investigating the kinematics and mechanics of the plate boundary deformation zone;* promote the use of standard procedures for geodetic data acquisition, quality evaluation, and processing, particularly GNSS data and InSAR data;* promote earthquake geodesy, the study of seismically active regions with large earthquake potential, and geodetic application to early warning system of earthquakes and tsunamis for hazard mitigation;* promote the role of geodesy in tectonic studies for understanding the seismic cycle, transient and instantaneous deformation, and creeping versus seismic slip on faults.* facilitate and stimulate the integrated exploitation of large data sets, using Machine Learning and Data Mining* support the organization of periodic workshops, meetings, summer schools with special emphasis on interdisciplinary research and interpretation and modeling issues* help to the emergence of a new generation of researchers in Seismogeodesy worldwideWe invite any researcher interested in Seismogeodesy to join us and have a fruitful discussion in front of our poster.

The coastal areas are being destroyed due to the usage that effect the natural balance. Unconsciously sand mining from the sea for nearshore nourishment and construction uses are the main ones. Physical interferences for mining of sand cause an ecologic threat to the coastal environment. However, use of marine sand is inevitable because of economic reasons or unobtainable land-based sand resources. The most convenient solution in such a protection–usage dilemma is to reduce negative impacts of sand production from marine. This depends on the accurate determination of criteriaon production place, style, and amount of sand. With this motivation, nearshore geodedic surveying studies performed on Kilyos Campus of Bogazici University located on the Black Sea coast, north of Istanbul, Turkey between 2001-2002. The study area extends 1 km in the longshore. Geodetic survey was carried out in the summer of 2001 to detect the initial condition for the shoreline. Long-term seasonal changes in shoreline positions were determined biannually. The coast was measured with post-processed kinematic GPS. Besides, shoreline change has studied using Landsat imagery between the years 1986-2015. The data set of Landsat 5 imageries were dated 05.08.1986 and 31.08.2007 and Landsat 7 imageries were dated 21.07.2001 and 28.07.2015. Landcover types in the study area were analyzed on the basis of pixel based classification method. Firstly, unsupervised classification based on ISODATA (Iterative Self Organizing Data Analysis Technique) has been applied and spectral clusters have been determined that gives prior knowledge about the study area. In the second step, supervised classification was carried out by using the three different approaches which are minimum-distance, parallelepiped and maximum-likelihood. All pixel based classification processes were performed with ENVI 4.8 image processing software. Results of geodetic studies and classification outputs will be presented in this paper.

Beneath the Marmara Sea, Turkey, the Main Marmara Fault (MMF), the offshore part of the North Anatolian Fault (NAF), is a well-known seismic gap for future M > 7 earthquakes. However, its detailed fault geometry and microearthquake activity have been debated for several decades. Using data acquired from long-term ocean bottom seismograph (OBS) observations, we made precise hypocenter estimations based on 3-D Vp and Vs velocity structures and assessed the fault geometry beneath the western and central parts of the MMF. The results indicate a segmentation boundary between the near-vertical western part and the south-dipping eastern part located around 28.10°E. Enriched OBS locations indicate microseismicity along both the inner and outer boundary faults of the Central Basin, especially on the western side. A comparison with previously published results suggests that the seismicity pattern has not changed for at least two years, between 2014 and 2016. Using a combined dataset of this and previous studies, lateral variations in the dip angle along the MMF fault segment from 27.4°E to 28.8°E were investigated. Based on this, we depicted on-fault seismicity along the MMF and defined three inactive areas of microseismicity. Two are located in the western segment, corresponding to the rupture area of the 1912 Ms. 7.4 earthquake, and the other, the largest, is located on the eastern segment. From a comparison of previous seismic and geodetic studies, it is considered that this area is a fully locked zone and has the potential for large earthquakes. Having compared the difference between hypocenter locations determined from OBSs and land-based stations, it is proposed that the epicentral locations of the mainshock and aftershocks of the September 26, 2019, M 5.7 earthquake are located much closer to the MMF than locations reported from only land-based results.

Strain analysis is one of the methods for the kinematic analysis of the repeated geodetic measurements. In order to derive strain accumulation in Marmara Region, different institutions carried out several Global Positioning System (GPS) campaigns in 1999 and 2006. The GPS campaigns were performed on the geodetic network which cover the provinces: Kirklareli, Tekirdag, Bursa, Bilecik and Adapazari. Then, the displacements of the network stations were estimated by means of analysing the GPS space geodetic measurements. For the assessment of the datum differences between 1999 and 2006 on the station coordinates, 3-D Helmert transformation was applied to the coordinates of each 1999 and 2006 datum. Then, a global test was introduced to determine the significant deformation which occurred in the geodetic GPS network. Strain accumulation with a finite element model was then computed. First, triangles were constructed for the whole network with the Delaunay method. Hereafter, strain parameters were calculated for each triangle. Maximum values of strain accumulation were found around the surroundings of Marmara Ereglisi and Izmit, whereas minimum values are around Istanbul.

The North Anatolian Fault (NAF) represents one of the most seismically active transform zones on Earth. It is characterized by high rates of crustal deformation that generate destructive earthquakes. These rates are induced by convergence of the northward-migrating Arabian and African plates with respect to the stable Eurasian plate. Therefore, the NAF represents a natural earthquake laboratory with a wide range of earthquake sizes (M ≤ 7.9) to investigate by using interdisciplinary approaches (seismological, magnetism, geological, gravitational, and geodetic studies). In this study, we compare the results of an analysis of b-values from seismicity and GPS (Global Positioning System) measurements of the strain rate to understand their coupling in terms of faulting and earthquake hazard implications. In particular, this comparison allows investigation of the spatial correlation between b-value and strain rate maps and is thus able to locate fault segments that have a high potential of generating large earthquake(s). b-Values range from 0.5 to 1.5 along the central NAF. The maximum principal strain rates are positive (tensile), and the minimum principal strain rates are negative (compressive). The surface strain is positive, showing that tensile strain is predominant in areas with high strain rates, consistent with the trend of the corresponding stresses.

WOS: 000450847400001, Greek-Turkish boundary near the cities Kos and Bodrum has been shaken on July 20, 2017 by a Mw6.6 earthquake. The mainshock is located offshore and did not generate an on-land surface rupture. Analyzing pre-and post-earthquake continuous/survey-type static GPS observations, we investigated co-seismic surface displacements at 20 sites to characterize source parameters and slip-distribution of the mainshock. Fault plane solutions as well as co-seismic slip distribution have been acquired through the inversion of co-seismic GPS displacements modeling the event as elastic dislocations in a half space. Fault plane solution shows a southward dipping normal-type fault segment extending a depth down to similar to 12 km, which remains within the brittle upper crust. Results from the distributed slip inversion show that the mainshock activated a similar to 65 km fault section, which has three high slip patches, namely western, central and eastern patches, where the coseismic slips reach up to 13, 26, and 5 cm, respectively. This slip pattern indicates that the pre-earthquake coupling, which is storing the slip deficit, occurred on these three patches., Research Foundation of Afyon Kocatepe University [17.FEN.BIL.35], This work was supportted by Research Foundation of Afyon Kocatepe University [project number 17.FEN.BIL.35].

The Aegean region and its surrounding area of Western Turkey is one of the most seismically active and rapidly deforming regions in the world. The study area, Izmir, is located between 26 degrees 15'-28 degrees 20 ' E longitude and 37 degrees 45'-39 degrees 15' N latitude in the Aegean region of Western Anatolia. The Tuzla Fault passes through Izmir, which is the third largest city in Turkey. In this study, we approach the problem of estimating and investigating the vertical displacements along the Tuzla Fault using a network of high precision levelling line. We established a levelling route with eight benchmarks, along the fault line. Six precise levelling campaigns were performed between 2009 and 2012, and the collected data in the surveying campaigns were processed by using the least-squares adjustment method and global testing in order to evaluate the vertical displacement. The results of the precise levelling indicated that the vertical displacements in the study area are not as significant in this period as were expected. However, compared with previous studies conducted in the same area, this study is different not only from the technique applied, but also it is carried out for the first time.

Geodetic measurements following the 23 October 2011, Mw = 7.2 Van (eastern Turkey) earthquake reveal that a fault splay on the footwall block of the coseismic thrust fault was reactivated and slipped aseismically for more than 1.5 years following the earthquake. Although long-lasting aseismic slip on coseismic ruptures has been documented following many large earthquakes, long-lasting, triggered slip on neighboring faults that did not rupture during the earthquake has not been reported previously. Elastic dislocation and Coulomb stress modeling indicate that the postseismic deformation can be adequately explained by shallow slip on both the coseismic and splay fault and is likely driven mostly by coseismic stress changes. Thus, the slip deficit on the shallow section of the coseismic fault indicated by interferometric synthetic aperture radar-based models has been partially filled by aseismic slip, suggesting a lower likelihood for a large earthquake on the shallow section of the Van fault than suggested by previous studies.

The Aegean region including western Turkey, mainland Greece, and the Hellenic Arc is the most seismological and geodynamical active domain in the Alpine Himalayan Belt. In this study, we processed 3 years of survey-mode GPS data and present the analysis of a combination of geodetic and seismological data around Izmir, which is the third most populated city in Turkey. The velocities obtained from 15 sites vary between 25 mm/yr and 28 mm/yr relative to the Eurasian plate. The power law exponent of earthquake size distribution (b-value) ranges from 0.8 to 2.8 in the Izmir region between 26.2 degrees E and 27.2 degrees E. The lowest b-value zones are found along Karaburun Fault (b = 0.8) and, between Seferihisar and Tuzla Faults (b = 0.8). A localized stress concentration is expected from numerical models of seismicity along geometrical locked fault patches. Therefore, areas with lowest b-values are considered to be the most likely location for a strong earthquake, a prediction that is confirmed by the 2005 M-w = 5.9 Seferihisar earthquake sequences, with epicentres located to the south of the Karaburun Fault. The north-south extension of the Izmir area is corroborated by extension rates up to 140 nanostrain/yr as obtained from our GPS data. We combined the 3-year GPS velocity field with the published velocity field to determine the strain rate pattern in the area. The spatial distribution of b-value reflects the normal background due to the tectonic framework and is corroborated by the geodetic data. b-Values correlate with strain pattern. This relationship suggests that decrease of b-values signifies accumulating strain. (c) 2013 Elsevier Ltd. All rights reserved.

Space-based tectonic studies on the western part of the North Anatolian Fault Zone (NAFZ) have been conducted over two decades. After the August 17, 1999, Izmit earthquake ( M w = 7.4), this region attracted greater scientific interest, and the collected data became more valuable. The Geodesy Department of the Kandilli Observatory and Earthquake Research Institute (KOERI) at Bogazici University established three micro-geodetic networks to the east of Akyazi, east of Iznik, and west of Lake Sapanca in the eastern part of the Marmara region; GPS data have been continually collected at these locations since 1994. The NAFZ branches out in the western part of the Marmara region and extends up to the Aegean Sea. Segments of the fault passing through the Marmara Sea are considered active, and this has increased concern regarding imminent earthquakes. Conventional geodetic measurements made between 1990 and 1994 are not sufficient for monitoring small movements. However, GPS has played a very important role in detecting such deformations in the area after 1994. The Iznik network, with 10 points, is bilaterally located on the Iznik-Mekece fault. Six years of GPS data for 2004–2010 collected for the monitoring of crustal deformation showed that the Iznik-Mekece fault segment moves westward at about 22 ± 1 mm/yr with respect to the Eurasia fixed reference frame. The GPS observations show that there is no strain accumulation in the area.

WOS: 000318381400003, Both seismological and geodynamic studies emphasize that the Aegean region is deforming internally mainly under pure shear stress and rotating in an anti-clockwise direction relative to the Eurasia plate. The Aegean region is seismically the most active region in western Anatolia, which comprises the Hellenic Arc, Greece, and western Turkey. Izmir is the third largest city in Turkey, with a population about 2.7 million in 2010. The Tuzla fault has a particular importance in terms of its proximity to the city of Izmir and its seismic activity. The Tuzla fault has NE-SW trending lineaments and lies between the towns of Menderes and Cape Doganbey. This study intended to investigate crustal deformation and relative displacement along the Tuzla fault and Izmir Bay by two different geodetic techniques: GPS and precise leveling. Toward this aim, a geodetic network consisting of 16 points has been established. The first GPS observation campaign and precise leveling measurements were performed in 2009, and the second set of measurements was performed in 2010. The data collected by the GPS campaigns were processed with GAMIT/GLOBK software. The displacements inferred from GPS data are between 21 mm/yr and 25 mm/yr with respect to Eurasia as the fixed reference frame. In addition, the precise leveling results show that there is a vertical displacement in the region of around 7 mm along the fault, which is higher than expected during a nine-month interval. (C) 2012 Elsevier Ltd. All rights reserved., TUBITAK-CAYDAG [108Y295]; Bogazici University Scientific Research Projects (BAP) [5056]; Geodesy Department of Kandilli Observatory; Earthquake Research Institute, The authors would like to thank the Geodesy Department of Kandilli Observatory and Earthquake Research Institute and the project's members for their support. We also thank Rob Reilinger and an anonymous reviewer for their comments and suggestions. We are grateful to the district governor of Seferihisar, officials of Izmir Metropolitan and Seferihisar Municipalities, and local people in the region for their help. Maps were drawn using GMT 4.5 (Wessel and Smith, 2001). This study was mainly supported by TUBITAK-CAYDAG under grant no. 108Y295 and Bogazici University Scientific Research Projects (BAP) under grant no. 5056.

For almost half a century, the Ismetpasa section of North Anatolian Fault (NAF) has been known to be creeping aseismically. During the past decades, there have been a number of investigations undertaken to monitor this movement using conventional surveying methods, GPS, LIDAR, and InSAR techniques. These studies have provided information on the length, depth and the rate of fault creep. We used GPS observations on a network of 5 survey points established in 1972 by the General Command of Mapping across the creeping segment to determine the present-day creep rate. This micro-geodetic network covers an area of approximately 1 km × 1 km on the 60 km long creeping section as determined from prior studies. GPS campaigns were carried out annually between 2005 and 2011. We found no evidence of a change in creep rate during this time period, consistent with some previous studies. On this portion of the creeping section, the creep rate is 7.6 ± 1 mm/yr, which is less than half of the annual average rate of relative plate velocity, indicating that significant strain is being accumulated on the fault. By comparing the present creep rate with earlier estimates, we conclude that the creep rate near Ismetpasa has been decreasing exponentially since the initial observations (1957–1969), and is likely the result of postseismic after slip following the 1944 (Mw 7.2) and/or 1951 (Mw 6.9) earthquakes that broke this segment of the fault.

The North Anatolian Fault Zone (NAFZ), which marks the boundary between Anatolia and the Eurasian plate, is one of the world's most seismically active structures. Although the eastern part of NAFZ has high seismic hazard, there is a lack of geodetic information about the present tectonics of this region. Even though many scientists would like to study this area, geographical and logistical problems make performing scientific research difficult. In order to investigate contemporary neotectonic deformation on the eastern NAFZ and in its neighborhood, a relatively dense Global Positioning System (GPS) monitoring network was established in 2003. Geodetic observations were performed in three GPS campaigns in an area of 350 km x 200 km with 12-month intervals. In addition, 14 new GPS stations were measured far from the deforming area. Since this region includes the intersection of the NAFZ and the East Anatolian Fault Zone (EAFZ), deformation is complex and estimating seismic hazard is difficult. One important segment is the Yedisu segment and it has not broken since the 1784 earthquake. After the 1992 Erzincan and 2003 Pulumur earthquakes, the Coulomb stress loading on the Yedisu segment of the NAFZ has increased significantly, emphasizing the need to monitor this region. We computed the horizontal velocity field with respect to Eurasia and strain rates field as well. GPS-derived velocities relative to Eurasia are in the range of 16-24 mm/year, which are consistent with the regional tectonics. The principal strain rates were derived from the velocity field. Results show that strain is accumulating between the NAFZ and EAFZ along small secondary fault branches such as the Ovacik Fault (OF). T.) (C) 2010 Elsevier Ltd. All rights reserved.

The geotechnical monitoring played an important role in guiding the tunneling applications during the construction of IZMIR LRTS (Light Rapid Transit System) 1st stage. The purpose of this paper is to review the deformation measurements and results gathered during the construction of LRTS 1st stage tunnels. The New Austrian Tunneling concept (NATM) was used for the construction of Ucyol–Konak conventional tunnels of the system. The EPBM (Earth Pressure Balance Method) concept used in the construction of Konak–Basmane precast segmental tunnels. Both tunneling concepts required monitoring of deformations during construction as well as for a period after its completion.

This study introduces the new results of a novel low-cost digital zenith camera system operated in Turkey that uses astronomical and geodetic instrumentation. Currently, it is possible to determine deflections of the vertical (DoV) components by using a vast amount of information gathered from geo-referenced star images, tilt measurements, and Global Navigation Satellite System technology. This new design of an astro-geodetic camera system is used for calculating DoV components with 12 independent solutions on a test station in Istanbul, and additional observations were performed to investigate the external accuracy of the system on a test network. A specific leveling method is developed to align system toward the zenithal direction. The final results of the observations on a test station located in Istanbul indicate that the accuracy of the system is about +/- 0.19 arc-seconds in latitude and +/- 0.28 arc-seconds in longitude determination. The system has been further tested on a network with 4 control points that have averagely 20km baselines. At the test network, the root mean square of the average value of the vertical deflections is calculated as +/- 0.36 arc-seconds. Furthermore, DoV components are compared with the values that are calculated using global geopotential models.

International audience; While the kinematics of Anatolia plate and the North Anatolian Fault System (NAFS) has been studied extensively, the slip rate and locking depth along the NAFS are usually assumed constant in the analyses due to the lack of sufficient data. This is also partly due to the reasonably good fit of Euler small circle and partly due to the lack of spatial resolution of observations to determine slip rates independently from locking depths. On the other hand, recent geodetic studies show a contrast for locking depth between Marmara and other parts of the NAFS, implying a non-uniform locking depth across the NAFS. In this study, we analyse new GPS data and homogenously combine available data sets covering the eastern part of the NAFS to form the most complete data set. In particular, we incorporate the first results of Turkish Real-Time Kinematic GPS Network (CORS-TR) into our data set. A detailed analysis of three profiles within the NAFS reveals an increase of locking depth in the middle profile to 19.1 ± 3.4 km from 11.9 ± 3.5 km in the easternmost profile while the slip rate is nearly constant (20–22 mm yr−1), which implies a variation of strain rate of ∼100 nanostrain yr−1. Assuming a constant locking depth throughout whole NAFS gives an average locking depth of 14.3 ± 1.7 km. Our best estimates of slip rates in block modelling which takes the variation of locking depths into account are in the range between 22.5 and 22.8 mm yr−1 over eastern part of the NAFS.

WEGENER is originally the acronym for Working Group of European Geoscientists for the Establishment of Networks for Earth-science Research. It was founded in March 1981 in response to an appeal delivered at the Journées Luxembourgeoises de Geodynamique in December 1980 to respond with a coordinated European proposal to a NASA Announcement of Opportunity inviting participation in the Crustal Dynamics and Earthquake Research Program. WEGENER, during the past 32 years, has always kept a close contact with the Agencies and Institutions responsible for the development and maintenance of the global space geodetic networks with the aim to make them aware of the scientific needs and outcomes of the project which might have an influence on the general science policy trends. WEGENER was serving as Inter-commission Project 3.2, between Commission 1 and Commission 3, of the International Association of Geodesy (IAG) until 2012. Since then, WEGENER project has became the Sub-commission 3.5 of IAG commission 3, namely Tectonics and Earthquake Geodesy. In this study, we briefly review the accomplishments of WEGENER as originally conceived and outline and justify the new focus of the WEGENER consortium. The remarkable and rapid evolution of the present state of global geodetic monitoring in regard to the precision of positioning capabilities (and hence deformation) and global coverage, the development of InSAR for monitoring strain with unprecedented spatial resolution, and continuing and planned data from highly precise satellite gravity and altimetry missions, encourage us to shift principal attention from mainly monitoring capabilities by a combination of space and terrestrial geodetic techniques to applying existing observational methodologies to the critical geophysical phenomena that threaten our planet and society. Our new focus includes developing an improved physical basis to mitigate earthquake, tsunami, and volcanic risks, and the effects of natural and anthropogenic climate change (sea level, ice degradation). In addition, expanded applications of space geodesy to atmospheric studies will remain a major focus with emphasis on ionospheric and tropospheric monitoring to support forecasting extreme events. Towards these ends, we will encourage and foster interdisciplinary, integrated initiatives to develop a range of case studies for these critical problems. Geological studies are needed to extend geodetic deformation studies to geologic time scales, and new modeling approaches will facilitate full exploitation of expanding geodetic databases. In light of this new focus, the WEGENER acronym now represents, “World Earthquake GEodesy Network for Environmental Hazard Research”.

The 17 August 1999 Izmit earthquake significantly deformed the earth's crust in the Marmara Region, especially in the Golcuk–Sapanca Zone, Turkey. It broke a 150-km long segment of the northern branch of North Anatolian Fault Zone. The geodetically determined moment magnitude was M w =7.5. Global Positioning System (GPS) sites, which are a small subset of the Marmara Continuous GPS Network (MAGNET), and survey sites in the region were studied to estimate coseismic and postseismic deformations, using different methodologies with linear, quadratic and exponential kinematic models. Six GPS epochs for these sites, which were carried out before and after the 17 August 1999 Izmit earthquake, were used to define the kinematic models. The quadratic deformation model was also applied to determine the time-dependent crustal movement parameters (velocity and acceleration) of the sites, using the Kalman filter technique. In order to show the differences between the models, the estimated deformation fields on the last epoch were compared. In all models, as expected, the faults near the sites show large coseismic displacements with fault parallel direction, whereas the far sites show small coseismic displacements due to the effects of the Izmit earthquake. Each kinematic model, fitted to the epochs after the earthquake, shows different behaviour. While the linear model shows insufficient results, the nonlinear models (quadratic and exponential) give the best fitted to the postseismic deformations. As a result of Kalman filter analysis, the fault near-sites shows significant velocities with fault parallel direction, whereas the far sites have insignificant velocities. All stations have insignificant accelerations in the last epoch.

The Marmara Sea region is deforming along the branches of the North Anatolian Fault (NAF), which is the boundary between the Anatolian and the Eurasian plates. We evaluate Global Positioning System (GPS) measurements performed from 1992 to 1999, up to the 17 August 1999 Izmit earthquake, to quantify the interseismic strain accumulation pattern in the Marmara Sea region. We compute interseismic velocities in a frame fixed to the Eurasian plate at 136 GPS points. To compute the frame-independent strain rates, we first smooth the north-south and the east-west velocity components separately to obtain the values at grid nodes, and then we compute directional derivatives and strain rates. Shear-strain rates reveal that the Marmara Sea region is within the plate boundary deformation zone having a width of about 110 km. The largest shear-strain rate accumulation is along the northern branch of the NAF, with maximum shear-strain rate reaching 220 nstrain/yr in the Marmara Sea. We calculate clockwise rigid body rotation rates with a maximum of 10 deg/m.y. along the northern branch while the Anatolian plate rotates anticlockwise. Dilatation rates display adjacent local tensional and compressional areas in the east-west direction within the Marmara Sea. Assuming the uniform simple shear, we compute the NAF slip rates vary between 11 and 26 mm/yr, with a minimum around Izmit, and increase east and west of Izmit. Manuscript received 30 August 2000.

We present and interpret the results of postseismic, Global Positioning System monitoring of the first 298 days following the 17 August 1999 Izmit earth- quake. Whereas the data suggest some spatial and temporal complexity in the post- seismic motions, the overall pattern can be characterized by time-dependent relaxa- tion functions and suggests exponential decay with an estimated 57-day relaxation time. The very rapid deformation during the first few weeks following the mainshock suggests rapid afterslip on and below the coseismic rupture segments. The exponen- tial decay of the postseismic deformations through the end of the observation period suggests contributions from the lower crustal viscoelastic relaxation.

We use Global Positioning System (GPS) observations and elastic half-space models to estimate the distribution of coseismic and postseismic slip along the Izmit earthquake rupture. Our results indicate that large coseismic slip (reaching 5.7 meters) is confined to the upper 10 kilometers of the crust, correlates with structurally distinct fault segments, and is relatively low near the hypocenter. Continued surface deformation during the first 75 days after the earthquake indicates an aseismic fault slip of as much as 0.43 meters on and below the coseismic rupture. These observations are consistent with a transition from unstable (episodic large earthquakes) to stable (fault creep) sliding at the base of the seismogenic zone.

During the past century, a series of predominantly westward migrating M>7 earthquakes broke an similar to 1000km section of the North Anatolian Fault (NAF). The only major remaining seismic gap along the fault is under the Sea of Marmara (Main Marmara Fault (MMF)). We use 20years of GPS observations to estimate strain accumulation on fault segments in the Marmara Sea seismic gap. We report the first direct observations of strain accumulation on the Princes' Islands segment of the MMF, constraining the slip deficit rate to 10-15mm/yr. In contrast, the central segment of the MMF that was thought to be the most likely location for the anticipated gap-filling earthquakes shows no evidence of strain accumulation, suggesting that fault motion is accommodated by fault creep. We conclude that the Princes' Islands segment is most likely to generate the next M>7 earthquake along the Sea of Marmara segment of the NAF.

GPS studies in Turkey date back to the early 1990s, but were mostly focused on the seismically active North Anatolian Fault System (NAFS), or on the more populated Western Anatolia. Relatively few studies were made of the seismically less-active East Anatolian Fault System (EAFS), although it has the potential to produce large earthquakes. In this study, we present the results of a combination of geodetic and seismological data around the Karliova Triple Junction (KTJ), which lies at the intersection of the North- and East Anatolian Fault Systems. In particular, the geodetic slip rates obtained through block modeling of GPS velocities were compared with b-values to assess seismicity in the region. Yedisu segment, one of the best-known seismic gaps in Turkey, was specifically analyzed. The relatively low b-values across Yedisu segment verify the accumulation of seismic energy in this segment, and the GPS-derived geodetic slip rates suggest that it has the potential to produce an earthquake of Mw 7.5 across an 80-km rupture zone. Additionally, analysis of earthquake data reveals that the study area has a ductile or rigid–ductile behavior with respect to its surroundings, characterized by varying b-values. Although, seismic events of moderate- to high magnitudes are confined along the major fault zones, there are also low-seismicity zones along the eastern part of the Bitlis Suture Zone and around Yedisu. Since the high seismicity areas within the region may not accumulate sufficient stress for a large earthquake to occur, it is considered that the deformation in such areas occurs in a ductile manner. On the other hand, the areas characterized by low b-values may have the capacity of stress accumulation, which could lead to brittle deformation.

In this study the hourly mean values of the geomagnetic data available in Turkey are analyzed to determine principal harmonics of the solar daily geomagnetic variations. Available data are grouped according to sunspot relative number to determine and analyzed for solar and lunar harmonics. The most disturbed five calendar days of the each month are removed in order to minimize the effect of current systems in the outer magnetosphere regions. Very good sunspot dependence found between solar harmonics and sunspot number.

International audience; Understanding the behavior of active faults in response to tectonic stresses is a critical issue in earthquake physics and seismic hazard assessments (Carpenter et al., 2011). While most active faults are unstable and move abruptly, releasing in seconds to a few minutes the strain accumulated around them for decades to centuries, some faults slip continuously, storing little or no strain and are therefore considered to be unlikely to produce signifi cant earthquakes as long as this behavior persists (Bürgmann et al., 2000). Although aseismic fault creep was fi rst reported over half a century ago along some major plate boundary faults, including the San Andreas fault in California (United States) and the North Anatolian fault in Turkey, the origin and physical processes of fault creep remain subjects of debate (Schleicher et al., 2010). Two primary, complementary, and competing mechanisms have been proposed to explain the mechanics of aseismic fault creep: (1) the presence of weak mineral phases such as clay and phyllosilicates in the bulk composition of fault zones (Carpenter et al., 2011) or the formation of highly localized, phyllosilicate-rich interconnected networks of shear planes or foliations (Collettini et al., 2009) via chemical and mechanical processes, and/ or (2) trapped fl uid overpressures within fault zones (Byerlee, 1990). Although recent observations (Lockner et al., 2011) support the idea that aseismic creep is controlled by the presence of weak rocks in the fault zone rather than by high fl uid pressures, analysis of rock samples from active (Holdsworth et al., 2011) and exhumed (Warr and Cox, 2001) fault zones suggests that transient fl uid overpressures do occur in many fault zones and are most likely generated during coseismic faulting due to shear heating, low per-meability, high water content, and low strength of clay-rich shear zones. Whether due to mineralogy and/or fl uid pressure affects, how or when stable aseismic surface creep initiates on active faults remains uncertain. The fact that creeping segments of the North Anatolian fault at Ismetpasa and the San Andreas fault in the San Francisco Bay area also rupture coseismically suggests to us that fault creep may be initiated as postseismic after-slip (Çakir et al., 2005; Schmidt et al., 2005), a mechanism that could not be confi rmed previously due to the lack of pre-and post-earthquake observations on these fault sections. In this study we use space geodetic data and recent fi eld observations along the A.D. 1999 Izmit earthquake rupture (Fig. 1) to demonstrate continuing afterslip that appears to grade into steady-state creep on a >60-km-long segment of the Izmit coseismic fault, supporting seismic slip as one of the possible mechanisms for initiating steady-state creep on mature strike-slip faults. THE 1999 IZMIT EARTHQUAKE The M w 7.4 Izmit earthquake on 17 August 1999 occurred on the North Anatolian fault

We report the results of nearly 7 years of postseismic deformation measurements using continuously recorded and survey mode GPS observations for the 1999 Izmit-Düzce earthquake sequence. Resolvable, time-dependent postseismic changes to the preearthquake interseismic velocity field extend at least as far as the continuous GPS station in Ankara, ∼200 km southeast of the Izmit rupture. Seven years after the earthquake sequence, the relative postseismic velocity across the North Anatolian Fault (NAF) reaches ∼10–12 mm/a, roughly 50% of the steady state interseismic rate, with the highest postseismic velocities within 40 km of the coseismic ruptures. We use a sequence of logarithmic time functions to fit GPS site motions. Up to three logarithmic terms with decay constants of 1, 150, and 3500 days are necessary to fit all the transient motion observed at the continuous GPS stations. The first term is required for the component of site motion parallel to the NAF at near-field sites strongly implicating rapid, shallow afterslip. The intermediate and longer-term postseismic velocity components reflect more broadly distributed strain with a symmetric double-couple pattern suggestive of either localized, deep afterslip or viscoelastic relaxation of the upper mantle and/or lower crust. In two areas (including the Marmara Sea) this pattern is superimposed on north-south extension centered on the NAF. We speculate that this extension may result from aseismic dip slip along coseismically weakened faults, driven by the background tectonic stress., Scientific and Technological Research Council of Turkey (CAYADAG Project 103Y100, EU 6), European Training Foundation (Frame FORESIGHT Project contract 511139), Scientific and Technological Research Council of Turkey (TARAL 1007 Project 105G019), National Science Foundation (U.S.) (grant EAR-0337497), National Science Foundation (U.S.) (grant EAR-0305480), National Science Foundation (U.S.) (grant INT-0001583), Natural Sciences and Engineering Research Council of Canada (Discovery grant RGPIN 261 458-07)