Vs30 değerine bağlı koherans modeli

Year 2020, Issue: 20, 111 - 119, 31.12.2020

Ebru Harmandar

https://doi.org/10.31590/ejosat.756187

Abstract

Depremlerin yol açtığı kuvvetli yer hareketi uzun yapıların her yerinde aynı olmayacaktır. Yer hareketindeki bu farklılığın, uzun yapıların tasarımı üzerinde önemli bir etkisi vardır. Depreme dayanıklı tasarımın, son yüzyıllarda deprem yer hareketinin değişkenliğini araştırmada etkisi olmuştur. Kuvvetli yer hareketinin bu değişkenliği, frekans veya zaman açısından tanımlanabilir. Bu çalışmada, koherans adı verilen frekans tanım alanı yönünden deprem yer hareketlerinin değişkenliği ele alındı. Bugüne kadar genelde, zemin etkisi dikkate alınmadan çeşitli koherans modelleri oluşturulmuştur. Bu bağlamda, 30 m derinliğin üstündeki ortalama kayma dalgası hızına (Vs30) bağlı olarak deprem yer hareketinin mekansal değişimi analiz edildi. İlk olarak, koherans değerleri İstanbul Deprem Acil Müdahale Sistemi tarafından kaydedilen altı depremin veriler kullanılarak hesaplandı. Koherans modelini elde etmek için duraklamalı koherans verileri dikkate alındı. Modelin kayıtlı verilerde en iyi sağlaması için doğrusal olmayan regresyon analizi kullanıldı. İkili istasyon gruplarının Vs30 değerlerine dayanarak bir katsayı tanımlandı. Bu Vs30 katsayısına bağlı koherans modeli; EW, NS ve dikey bileşenler için oluşturuldu. Beklendiği üzere, frekans ve istasyonlar arası mesafesinin artmasıyla koherans fonksiyonunun azaldığı gözlendi. Vs30 katsayısındaki azalma, koherans değerlerinde artışa neden oldu. EW ve NS bileşenleri için üretilen koherans modelleri arasındaki fark oldukça küçüktür. Düşey bileşen için üretilen model yatay için üretilenden farklıdır. Gelecekteki çalışmalarda, elde edilen koherans modeli uzun yapıların depreme dayanıklı tasarımı için mekansal değişen yer hareketlerini simüle etmek için kullanılır.

Keywords

Depremler, İstanbul Deprem Erken Uyarı sistemi, Koherans Modeli, Vs30

Vs30-based Coherency Model

Abstract

Strong ground motion caused by earthquakes at every point of extended structures would not be same. This difference in ground movement has an important effect on the design of these types of structures. Meanwhile, the seismic resistant design has been lead to investigate the variability of earthquake ground motion over last decades. This variability of strong ground motion can define in terms of frequency or time. In this study, frequency domained variability named coherency is considered. Several coherency models have been proposed without considering soil effect. In this context, spatial variation of seismic ground motion based on the average shear wave velocity over the upper 30 m of depth, Vs30 is analyzed. Initially, coherency values are calculated using data triggered during six earthquakes recorded by the Istanbul Earthquake Rapid Response System. Lagged coherency data is considered in the process to get the coherency model. Nonlinear regression analysis is used for the model to obtain a good-fit to observed data. A coefficient is defined based on Vs30 values of the station-pairs. The cohereny model based on this coefficient of Vs30 is derived for EW and NS components. It is expected that coherency function decreases with the increase of frequency and separation distance. The decrease in the coefficient of Vs30 causes decrease in coherency. The variance in the coherency model between EW and NS components is small. This coherency model is used to simulate spatial variable ground motion for the accurate seismic design of elongated structures for the future studies.

Keywords

Earthquakes, Istanbul Earthquake Rapid Response System, Coherency Model, Vs30

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