Evaluation of the Effect of Source Time Function in Numerical Ground Motion Simulations

Öz

One of the well-known tools for understanding earthquake source, path, and site effects is ground motion simulation studies. Each parameter that affects different frequency ranges needs to be well defined separately before the simulation. In the first step, to obtain a reliable source model (strike, dip, rake), it is necessary to utilize available local and teleseismic earthquake data. Then, if the path and site parameters are known for a site, defining the characteristic source model and investigating the source time function are necessary to obtain well-matched ground motions. The main purpose of the study is to investigate the source time function for catching low and high frequency content of waveforms by ground motion simulation studies. For this aim, triangle, smoothed ramp, and Kostrov-like slip velocity functions are investigated using the 2017 Ayvacık (Mw 5.3) and 2017 Midilli (Mw 6.3) earthquakes, with characteristic source models and rupture propagation. The results indicate that different source time functions with the same characteristic frequency generate the same synthetic waveforms and Fourier spectrum due to large station distances and spectrum averaging of waveform summation in the time domain. The Kostrov-like slip velocity function, which is used in ground motion simulations, is an appropriate function for generating high frequency content without changing the characteristic source model of an earthquake.

Anahtar Kelimeler

• 1D numerical ground motion simulation
• Discrete wave number method
• Earthquake source model
• Kostrov-like slip velocity function
• Source time function

Proje Numarası

118Y003

Nümerik Yer Hareketi Simülasyonlarında Kaynak Zaman Fonksiyonu Etkisinin Değerlendirilmesi / Evaluation of the Effect of Source Time Function in Numerical Ground Motion Simulations

Öz

Deprem kaynağı, deprem dalgalarının yayıldığı ortam ve zemin etkilerini anlamaya yönelik iyi bilinen araçlardan biri yer hareketi simülasyonu çalışmalarıdır. Simülasyondan önce, farklı frekans aralıklarını etkileyen her bir parametrenin ayrı ayrı ve doğru şekilde tanımlanması gerekmektedir. İlk aşamada, güvenilir bir kaynak modeli (doğrultu, eğim ve kayma açısı) elde edebilmek için mevcut yerel ve telesismik deprem verilerinden yararlanılması gereklidir. Daha sonra, bir istasyona ait yayılım yolu ve zemin parametreleri biliniyorsa, iyi uyum sağlayan yer hareketlerini elde edebilmek için karakteristik kaynak modelinin tanımlanması ve kaynak zaman fonksiyonunun incelenmesi gerekmektedir. Bu çalışmanın temel amacı, yer hareketi simülasyonlarında düşük ve yüksek frekans içeriğini elde edebilmek amacıyla kullanılan kaynak zaman fonksiyonlarının etkilerinin araştırılmasıdır. Bu amaçla, üçgen, yumuşatılmış rampa ve Kostrov-benzeri kayma hızı fonksiyonları, karakteristik kaynak modelleri ve yırtılma yayılımı ile birlikte 2017 Ayvacık (Mw 5.3) ve 2017 Midilli (Mw 6.3) depremleri kullanılarak incelenmiştir. Sonuçlar, aynı karakteristik frekansa sahip farklı kaynak zaman fonksiyonlarının, istasyon uzaklıklarının büyük olması ve zaman ortamında gerçekleştirilen dalga şekli toplamının spektrum yuvarlaklaştırması nedeniyle, aynı sentetik dalga şekillerini ve Fourier spektrumunu ürettiğini göstermektedir. Yer hareketi simülasyonlarında kullanılan Kostrov-benzeri kayma hızı fonksiyonu, bir depremin karakteristik kaynak modelini değiştirmeden yüksek frekans içeriği üretmek için diğerlerine göre daha uygun bir fonksiyon olduğu değerlendirilmiştir.

Anahtar Kelimeler

• 1B nümerik yer hareketi simülasyonu
• Ayrık dalga sayısı yöntemi
• Deprem kaynak modeli
• Kaynak zaman fonksiyonu
• Kostrov-benzeri kayma hızı fonksiyonu

Destekleyen Kurum

TÜBİTAK

Proje Numarası

118Y003

Kaynakça

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