Abstract
The identification and measurement of ground deformations in urban areas is of great importance for determining the vulnerable parts of the cities that are prone to geohazards, which is a crucial element of both sustainable urban planning and hazard mitigation. Interferometric synthetic aperture radar (InSAR) time series analysis is a very powerful tool for the operational mapping of ground deformation related to urban subsidence and landslide phenomena. With an analysis spanning almost 25 years of satellite radar observations, we compute an InSAR time series of data from multiple satellites (European Remote Sensing satellites ERS-1 and ERS-2, Envisat, Sentinel-1A, and its twin sensor Sentinel-1B) in order to investigate the spatial extent and rate of ground deformation 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 velocity maps of ground surface displacement in selected areas of Istanbul. We identify several sites along the terrestrial and coastal regions of Istanbul that underwent vertical ground subsidence at varying rates, from 5 ± 1.2 mm/yr to 15 ± 2.1 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 ± 2 mm/yr. We show that subsidence has been occurring along the Ayamama river stream at a rate of up to 10 ± 1.8 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 ± 1.2 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 ± 2.3 mm/yr starting in 2016 around one of the highest skyscrapers of Istanbul, which was built in 2010.
Highlights
Very rapid social and economic transformation in recent decades caused a huge rural-to-urban migration all over the world, which has fueled urban growth
We identified several sites along the terrestrial and coastal region of Istanbul that have been undergoing vertical ground subsidence at rates ranging from 5 mm/yr to 15 mm/yr
A permanent scatterers (PS)-Interferometric synthetic aperture radar (InSAR) time series analysis was performed using 291 C-band SAR images in order to characterise these subsidence phenomena by combining multi-track/sensor InSAR datasets and provide insights into the potential hazards induced by local soil conditions and human activities
Summary
Very rapid social and economic transformation in recent decades caused a huge rural-to-urban migration all over the world, which has fueled urban growth. According to the Istanbul Transportation Master Plan (ITMP), when taking into account the consequence of Turkey’s economic growth in the last two decades and the large amount of immigration, projections indicate that the population will overcome 20 million inhabitants in 2023 [2] This rapid population growth poses major threats to the city’s development when considering its vulnerability to natural disasters such as earthquakes, landslides, and floods, due to heavy and unplanned urbanization practices. TThhee PPaalleeoozzooiicc mmeettaammoorrpphhiicc bbaasseemmeenntt ooff tthhee ssttuuddyy aarreeaa ccoonnssiissttss iinn tthhee eeaasstt iinn aa tthhiicckk ttuurrbbiiddiittiicc ssaannddssttoonnee––sshhaallee sseeqquueennccee ooff tthhee CCaarrbboonniiffeerroouuss aaggee,, wwhhiillee tthhee EEoocceennee ccoovveerr iiss mmaaddee ooff lliimmeessttoonnee,, mmaarrll,, aanndd ccllaayyssttoonnee uunniittss,, wwhhiicchh aarree ttrraannssggrreessssiivvee oonn ÇÇaattaallccaa mmeettaammoorrpphhiicc uunniittss iinn tthhee wweesstt ((FFiigguurree 22)).
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