İstanbul Avcılar Heyelanı Üzerinde VLF ve ERT Yer İletkenlik Modellerinin Kıyaslanması

Yıl 2019, Cilt: 40 Sayı: 2, 190 - 209, 15.08.2019

Gökhan Karcıoğlu , Rafet Ender Alemdar Leyla Evgi

https://doi.org/10.17824/yerbilimleri.549104

Öz

VLF ve ERT yöntemleri, yerin ilk birkaç
on metresindeki iletkenlik dağılımının araştırılmasında sıklıkla
kullanılmaktadır. VLF yöntemi, hızlı ve düşük maliyetli ölçü alınmasına olanak
sağlamaktadır, ancak, az sayıda ve nispeten dar bir frekans aralığında ölçü alınması,
ERT yöntemine göre düşük derinlik çözünürlüğü sunmaktadır. Bu nedenle, ERT yöntemi,
genelde önemli iletkenlik karşıtlıklarının görüldüğü heyelanlı ortamlarda en
çok kullanılan yöntemler arasındadır.

Heyelanlar üzerinde VLF verilerinin 2B ters
çözüm sonuçlarının ne kadar başarılı sonuçlar sağladığının araştırılması için İstanbul
Avcılar heyelanı üzerinde paralel iki hat üzerinde VLF-EM ve ERT ölçümleri gerçekleştirilmiştir.
Ayrıca VLF-EM hattının Kuzeydoğu ucunda VLF-R verileri de toplanmıştır. Toplanan
veriler, birbirinden bağımsız olarak 2B yuvarlatıcılı ters çözüm algoritmaları
ile modellenmiş ve yorumlanmıştır.

Sonuçlara göre, heyelan içerisindeki
iletkenler ve kayma düzlemi, VLF yöntemi ile belirlenebilmiştir. Buna göre,
kayma düzlemini teşkil eden Gürpınar formasyonunun iletken killeri 15-20m
derinde tespit edilmiştir. VLF-EM yöntemi, yatay iletkenlik değişimlerin
duyarlı olduğundan, yüzeyi kaplayan iletken alüvyon VLF-EM verileri ile belirlenememiştir.
Çalışma alanının Kuzeydoğu bölümünde, Gürpınar formasyonunun killerinin
yeryüzüne yaklaştığı hem ERT hem de VLF-EM yöntemi ile belirlenmiştir. Çalışma
alanının Kuzeydoğu ucunda alüvyon örtü ve ~3-10m derindeki iletken killer
VLF-EM modelinde birbirinden ayıramamıştır. Buna karşın, VLF-R ölçüleri ile
daha yüksek düşey ayrımlılık elde edilebildiğinden, bu iletkenlerin başarılı
bir şekilde birbirinden ayrılması mümkün olmuştur. 

Anahtar Kelimeler

VLF, ERT, 2B Ters Çözüm, Avcılar Heyelanı

Comparison of the VLF and ERT Geo-Electrical Models on the Avcılar Landslide (Istanbul, Turkey)

Öz

VLF and ERT methods are widely used for investigating the resistivity distribution in
the first few ten meters of the earth. VLF method provides rapid and low-cost
measurements; however, the low frequency count and the relatively narrow
frequency band provide a lower depth of investigation, compared to that of the ERT
method. Hence, ERT is amongst the most employed methods in the landslides areas
where sharp resistivity contrasts are generally observed.
To investigate the performance of the 2D inversion results of the VLF data on
landslide areas, VLF-EM and ERT measurements are acquired on two parallel
profiles. Besides, VLF-R measurements are performed on the northeastern end of
the VLF-EM profile. The measured data are modeled and interpreted individually,
using 2D smooth inversion algorithms.
The results suggest that conductive zones and the sliding surface of the landslide are
delineated using the VLF method. Accordingly, conductive clays of the Gürpınar
formation, consisting of the sliding surface, are delineated between 15-20 m depth.
Due to the sensitivity of the VLF-EM data to the horizontal conductivity differences,
the conductive alluvium cover is not delineated from the VLF-EM data. In the
northeastern part of the study area, clays of the Gürpınar formation are observed to
be approaching to the surface, detected from both VLF-EM and ERT models. In the
northeasternmost part of the study area, VLF-EM model failed to detect the alluvium
cover separately from the conductive clays at ~3-10 m depth. However, due to the
higher vertical resolution obtained from the VLF-R measurements, these conductors
are successfully identified by the VLF-R model.

Anahtar Kelimeler

VLF, ERT, 2D inversion, Avcılar landslide

Kaynakça

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