Yazar "Aslan, Gökhan" ile Avrasya Yer Bilimleri Enstitüsü'a göz atma
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ÖgeMonitoring of surface deformation in northwest turkey from high resolution insar : Focus on tectonic aseismic slip and subsidence(Eurasia Institute of Earth Sciences, 2019-03-19) Aslan, Gökhan ; Çakır, Ziyadin ; 602142001 ; Solid Earth Sciences ; Katı Yer BilimleriGeohazards, such as earthquakes, land subsidence and uplift, ground settlement, landslides and volcanoes cause static and/or dynamic surface deformation and pose major threat to human life and structures. Especially in earthquake-prone areas, understanding the spatial and temporal evolution of surface displacement and the underlying mechanisms responsible for these displacements is of great importance for geohazard mitigation. The Anatolian plate is bounded by the right-lateral North Anatolian Fault (NAF) and the left-lateral East-Anatolian Fault to the north and east-southeast of Turkey, respectively. It is moving westward due to the convergence of the Arabian and Eurasian plates and the slab subduction at the Hellenic Trench. The 1600-km-long NAF is a major continental strike-slip fault, known as one of the most prominent active faults in the eastern Mediterranean region, with an average slip rate of 24±2 mm/yr. This right-lateral fault ruptured between 1939 and 1999 in a sequence of eight M>7 earthquakes, with a westward migration that started near Erzincan in the east and reached the western shore of Marmara Sea in the west. This migration has been explained by the Coulomb stress transfer during and between successive earthquakes along fault strike. Between the western end of this sequence, and the eastern end of the 1912 earthquake to the east of the Marmara sea, a ~70 km-long section of the NAF defines a major seismic gap very close to the megacity of Istanbul. Assessment of seismic hazard in the Marmara sea region suggests that a large and destructive earthquake (M>7) may occur with a probability of 35-70% in the next 30 years on this fault section, 20 km south of Istanbul. Refined assessment of seismic hazard, from precise measurements of tectonic ground deformations in particular, is therefore profoundly important for prevention of any widespread damage and destruction in the region. This region is also affected by an important population growth and industrial and land exploitation development, implying other types of hazards. The aim of this thesis is therefore centered on the detection and monitoring of surface deformation in northwest Turkey induced by a variety of natural (such as tectonic activity, slow moving-landslides, etc.) and anthropogenic (ground water extraction, construction activities, etc.) hazards and on the analysis of the related deformation mechanisms and their environmental consequences. In this work, I computed Interferometric Synthetic Aperture Radar (InSAR) time series to examine ground deformation evolution for three different case studies associated to different geophysical phenomena and underlying processes. The focus of this thesis is two-fold : (1) to reveal and monitor the spatio-temporal characteristics of aseismic slip along the August 17, 1999 Mw 7.4 Izmit earthquake rupture, and discuss its potential relationship with lithology and geology (2) to investigate ground subsidence in urban or human-exploited areas induced by various factors, and discuss the relative roles of tectonics, lithology and anthropogenic activities in such ground motion. In the first case-study, I combined InSAR measurements, based on X-band TerraSAR-X and C-band Sentinel-1 A-B radar images acquired over the period 2011-2017, with near field GPS measurements, performed every 6 months from 2014 to 2016, as well as creep meter measurements to examine the surface velocity field around the NAF after the 1999 Izmit earthquake. In this study, the Stanford Method for Persistent Scatterers InSAR package (StaMPS) was employed to process series of Sentinel 1 A-B (acquired along ascending and descending orbits) and TerraSAR-X (ascending orbits) radar images. The InSAR horizontal mean velocity fields reveal that the creep rate on the central segment of the 1999 Izmit fault rupture continues to decay, more than 19 years after the earthquake, in overall agreement with models of postseismic afterslip rate decaying logarithmically with time. Along the fault section that experienced a supershear velocity rupture during the Izmit earthquake, creep continues with a rate up to ~ 8 mm/yr. A significant transient event with accelerating creep is detected in December 2016 on the Sentinel-1 time series, consistent with creepmeter measurements, near the maximum creep rate location. It is associated with a total surface slip of 10 mm released in one month only. Complementary analyses of the vertical velocity fields show a persistent subsidence on the hanging wall block of the Golcuk normal fault that also ruptured during the Izmit earthquake. Our results demonstrate that afterslip processes along the North Anatolian Fault east-southeast of Istanbul are more complex than previously proposed as they vary spatio-temporally along the fault. The second case study deals with the identification and measurement of secular ground deformation in Istanbul from a long-term InSAR time-series spanning almost 25 years of satellite radar observations (1992-2017). This InSAR time series was computed from radar images of multiple satellites (ERS-1, ERS-2, Envisat, Sentinel-1 A, B) in order to investigate the spatial extent and rate of ground subsidence in the megacity of Istanbul. By combining the various multi-track InSAR datasets (291 images in total) and analysing persistent scatterers (Ps-InSAR), we present mean line of sight velocity maps fields and project them into ground surface velocity maps in selected areas of Istanbul. Various sites along the terrestrial and coastal regions of Istanbul are found to be undergoing vertical ground subsidence at varying rates from ~5 mm/yr to ~15 mm/yr. The results reveal that the most distinctive subsidence patterns are associated with both anthropogenic factors and relatively weak lithologies along the Haramirede valley in particular, where the observed subsidence is up to ~10 mm/yr. We show that subsidence has been occurring along the Ayamama river at a rate of up to ~10 mm/yr since 1992, and has also been slowing down over time following the restoration of the river and stream system. We also identify subsidence at a rate of ~8 mm/yr along the coastal region of Istanbul which we associate with land reclamation, as well as a very localised subsidence at a rate of ~15 mm/yr starting in 2016 around one of the highest skyscrapers of Istanbul, that was built in 2010. In the third case study, InSAR time-series analysis is calculated for quantifying the subsidence of the Bursa Plain (southern Marmara region of Turkey), which has been interpreted as resulting from tectonic motions in the region. In this study, the StaMPS is employed to process series of Sentinel 1 A-B radar images acquired between 2014 and 2017 along both ascending and descending orbits. The vertical velocity field obtained after decomposition of line-of-sight velocity fields on the two tracks reveals that the Bursa plain is subsiding at rates up to 25 mm/yr. The most prominent subsidence signal in the basin forms an east-west elongated ellipse of deformation in the east, and is bounded by a Quaternary alluvial plain undergoing average vertical subsidence at ~10 mm/yr. Another localized subsidence signal is located 5 km north of the city, following the Bursa alluvial fan, and is subsiding at velocities up to 25 mm/yr. The comparison between temporal variations of the subsiding surface displacements and variations of the water pressure head in the aquifer allows estimation of the compressibility of the aquifer, α. It falls in the range of 0.5×〖10〗^(-6)-2×〖10〗^(-6) Pa−1, which corresponds to typical values for clay and sand sediments. We find a clear correlation between subsidence patterns and the lithology, suggesting a strong lithological control over the observed subsidence. In addition, the maximum rate of ground subsidence occurs where agricultural activity relies on groundwater exploitation. The InSAR time series within the observation period is well correlated with changes in the depth of the ground water. These observations indicate that the recent acceleration of subsidence is mainly due to anthropogenic activities rather than tectonic motion. Finally, this dissertation emphasizes the potentialities of the methodology of InSAR time-series analysis to efficiently map millimetre-scale deformation for different geophysical phenomena along the selected region in northwest Turkey. To better understand the mechanism of crustal deformation and differentiate slow surface deformations driven by human and regular tectonic activities, further work, complementary to InSAR, would be required to enable the monitoring and forecasting of region-wide geohazards.