Site Effects in Avcilar, West of Istanbul, Turkey, from Strong- and Weak-Motion Data

Özel, Oğuz; Cranswick, Edward; Meremonte, Mark; Erdik, Mustafa; Şafak, Erdal

doi:10.1785/0120000827

Cited by 39 publications

(14 citation statements)

References 11 publications

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“…Practice shows that a thick sedimentary cover usually generates spectra with peaks at low frequencies (1-3 Hz) while thin sediments usually generate high frequency peaks (>10 Hz). A flat spectrum with constant amplitude is expected for sites situated on crystalline outcrops (Bard 1994;Bard et al 2004;Nakamura 1989Nakamura , 2000. The results of the present survey are maps showing the distribution of the fundamental site frequency and the observed amplification factors.…”

Section: Introductionsupporting

confidence: 54%

An investigation of the significance of local site effects in Plovdiv, Bulgaria

Kandilarov

Atakan

Havskov

et al. 2008

Bull Earthquake Eng

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Plovdiv is the second largest city in the Republic of Bulgaria. A large part of the city is located on Holocene alluvial sediments and the oldest neighborhoods are situated on syenitic rock outcrops. We believe that local site effects may be an important contributor to the destruction caused by earthquakes. The primary objective of this study was to estimate quantitatively the local site effects in the central area of Plovdiv in terms of fundamental site frequency and amplification factor. Another important objective was to see how these correlate with the geological structures underlying the city. Measurements of the seismic noise at more than two hundred regularly placed points were made in the central area of the city. The H/V spectra were then calculated and analyzed to determine the spatial distribution of the fundamental site frequency and the amplification factor. The results exhibit very good correlation with the local geology. They were also compared with an intensity map from the strong 1928 Plovdiv earthquake. The comparison clearly demonstrates that the local site effects were the main factor in the destruction of buildings-the zones where the most damage was observed are also the zones where we have low fundamental site frequencies and high amplifications. Similarly the areas with high fundamental site frequencies and low amplification factors cover the neighborhoods where less damage has been observed. This study may form a basis for a more comprehensive and systematic microzonation study in Plovdiv.

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Section: Introductionsupporting

confidence: 54%

An investigation of the significance of local site effects in Plovdiv, Bulgaria

Kandilarov

Atakan

Havskov

et al. 2008

Bull Earthquake Eng

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“…Previous studies of local site effects, following the 1999 Izmit and Düzce earthquakes, have focused mainly on the Avcilar district of western Istanbul (e.g. Özel et al 2002; Tezcan et al 2002), and on the city of Adapazari in the east (e.g. Bakir et al 2002; Komazawa et al 2002; Sancio et al 2002; Beyen & Erdik 2004; Ansal et al 2004), which experienced significant damage mainly due to site effects.…”

Section: Introductionmentioning

confidence: 99%

Local site effects in Ataköy, Istanbul, Turkey, due to a future large earthquake in the Marmara Sea

Sørensen

Oprsal

Bonnefoy-Claudet

et al. 2006

Geophysical Journal International

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S U M M A R YSince the 1999 Izmit and Düzce earthquakes in northwest Turkey, many seismic hazard studies have focused on the city of Istanbul. An important issue in this respect is local site effects: strong amplifications are expected at a number of locations due to the local geological conditions. In this study we estimate the local site effects in the Ataköy area (southwestern Istanbul) by applying several techniques using synthetic data (hybrid 3-D modelling and 1-D modelling) and comparing to empirical data. We apply a hybrid 3-D finite-difference method that combines a complex source and wave propagation for a regional 1-D velocity model with site effects calculated for a local 3-D velocity structure. The local velocity model is built from geological, geotechnical and geomorphological data. The results indicate that strongest spectral amplifications (SA) in the Ataköy area occur around 1 Hz and that amplification levels are largest for alluvial sites where SA reaching a factor of 1.5-2 can be expected in the case of a large earthquake. We also compare our results to H/V (horizontal to vertical component of the recorded signal) spectral ratios calculated for microtremor data recorded at 30 sites as well as to ambient noise synthetics simulated using a 1-D approach. Because the applied methods complement each other, they provide comprehensive and reliable information about the local site effects in Ataköy. Added to that, our results have significant implications for the southwestern parts of Istanbul built on similar geological formations, for which, therefore, similar SA levels are expected.

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“…The maximum ground acceleration that was measured on soft sediments was 0.25 g, which is six times higher than the peak ground acceleration recorded on the bedrock in the center of Istanbul [40]. This difference is the result of the amplification of seismic waves in surficial layers with soft lithology [40,[42][43][44][45][46]. Despite a low background seismicity, which suggested no active faulting in the region [47], destructive and widespread damage during the 1999 Izmit earthquake drew considerable attention on this area, requiring the reassessment of active faulting.…”

Section: Study Area 1: Haramidere Valley and Avcilar Neighborhoodmentioning

confidence: 99%

Analysis of Secular Ground Motions in Istanbul from a Long-Term InSAR Time-Series (1992–2017)

et al. 2018

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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.

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Site Effects in Avcilar, West of Istanbul, Turkey, from Strong- and Weak-Motion Data

Cited by 39 publications

References 11 publications

An investigation of the significance of local site effects in Plovdiv, Bulgaria

An investigation of the significance of local site effects in Plovdiv, Bulgaria

Local site effects in Ataköy, Istanbul, Turkey, due to a future large earthquake in the Marmara Sea

Analysis of Secular Ground Motions in Istanbul from a Long-Term InSAR Time-Series (1992–2017)

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