Eskişehir havzasında H/V ve SPAC yöntemleriyle sismik analiz ve derinlik profili çalışmaları

Yıl 2024, Cilt: 14 Sayı: 3, 883 - 909, 15.09.2024

Mehmet Safa Arslan , Asım Oğuz Özel

https://doi.org/10.17714/gumusfenbil.1469624

Öz

0.1 saniyeden 10 saniyeye kadar olan geniş bir periyot aralığındaki yer hareketlerinin özelliklerini belirlemek, sismik risk değerlendirmesi için kritik önem taşır. Eskişehir ili, yaklaşık bir milyon nüfusu ve gelişmekte olan sanayisi ile, sismik aktivitesi nispeten düşük olmasına rağmen, hızlı yapılaşma sebebiyle yüksek sismik riske sahip bir bölge olarak değerlendirilmektedir. Sismik hızların belirlenmesi ve anakaya derinliğinin tespit edilmesi, yapılaşma ve deprem risklerinin azaltılması için önem taşımaktadır. Yapılan çalışma, bu bilgilerin elde edilmesi amacıyla gerçekleştirilmiştir. Araştırma, 15 farklı noktada, 2017 ve 2018 yıllarında toplamda gerçekleştirilen 7 ve 8 ağ ölçümleri ile desteklenmiştir. Mikrotremor ölçümleri, tek-istasyon Yatay/Düşey spektral oran (H/V) metodu ve ağ ölçmeleri ile SPAC yöntemi kullanılarak, 600-700 m derinliklere kadar Vs yapısının belirlenmesine olanak tanımıştır. Elde edilen veriler, ters çözüm yöntemleri kullanılarak yeraltı derinlik modellemesi oluşturmak için kullanılmıştır. Eskişehir ovasının ortasında, küçük ve büyük ağ/dizilim ölçmeleri ile sığ kısımlar için 100-250 m derinliklerde ve 500-800 m/sn hızlarda mühendislik anakayası tespit edilmiştir. Batıda 1100 m/sn'den doğuda 1800 m/sn'ye kadar değişen S dalgası hızları ve ortalama 600-800 m derinlikte sismolojik anakaya belirlenmiştir. Mikrotremor çalışmaları, batıdan doğuya ve güneyden kuzeye derinleşen ve en derin noktada 800 m'ye ulaşan anakaya derinliklerini göstermektedir. Yüzey dalgaları dispersiyon eğrilerinden elde edilen sismolojik anakayanın Vs hızı 1200-1800 m/sn arasında değişmektedir. Sonuç olarak, Eskişehir havzası ve benzeri alanlarda, detaylı jeolojik ve jeofiziksel analizlerin sismik risk değerlendirmeleri ve tehlike analizleri için büyük öneme sahip olduğu belirlenmiştir. Havza etkilerinin bir başka deyişle yerel zemin etkilerinin, yani yer hareketi büyütmelerinin, sismik hasar analizlerindeki kritik rolü bu çalışma ile bir kez daha vurgulanmıştır.

Anahtar Kelimeler

Anakaya, Eskişehir, H/V yöntemi, Mikrotremor, S dalga hızı, SPAC yöntemi

Seismic Analysis and Depth Profile Studies Using H/V and SPAC Methods in the Eskişehir Basin

Öz

Determining the characteristics of ground motions in a wide period range of 0.1 to 10 seconds is crucial for seismic risk assessment. Eskişehir province, with a population of approximately one million and a developing industry is a high seismic risk region despite its relatively low seismic activity due to rapid urbanization. Determining seismic velocities and bedrock depths is important for reducing urbanization and earthquake risks. This study was conducted to obtain this information. The research, supported by 7 and 8 network measurements performed at 15 different points in total in 2017 and 2018, allowed the determination of the Vs structure up to depths of 600-700 m using microtremor measurements with the single-station Horizontal/Vertical spectral ratio (H/V) method and network measurements with the SPAC (Spatial Autocorrelation) method. The data obtained were used to create a subsurface depth model using inverse solution methods. Engineering bedrock was detected at depths of 100-250 m and velocities of 500-800 m/s for shallow sections using small and large network/array measurements in the middle of the Eskişehir plain. S-wave velocities ranging from 1100 m/s in the west to 1800 m/s in the east and seismological bedrock at an average depth of 600-800 m were determined. Microtremor studies show bedrock depths that deepen from west to east and south to north, reaching 800 m at the deepest point. The Vs velocity of the seismological bedrock obtained from surface wave dispersion curves varies between 1200-1800 m/s. In conclusion, detailed geological and geophysical analyses are of vital importance for seismic risk assessments and hazard analyses in the Eskişehir basin and similar areas. The critical role of local ground effects, i.e., ground motion amplifications, in seismic damage analysis was once again emphasized by this study.

Anahtar Kelimeler

Bedrock, Eskisehir, H/V method, Microtremor, S wave velocity, SPAC method

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