Rayleigh Dalgası Dispersiyon Eğrisinin Elde Edilmesinde Özilişki Hesaplama Yöntemlerinin Farklı Geometrik Dizilimlerle Karşılaştırılması

Öz

Geometrik dizilimli ortam gürültüsü ölçümü, yüzeye yakın jeolojik birimlerin dinamik özelliklerini belirlemede etkili bir yöntem olup, istasyon kayıtlarının birleştirilmesi sayesinde sinyal-gürültü oranını artırarak kentsel alanlarda yapılacak çalışmalarda önemli avantajlar sağlar. Böylece tek istasyonla tespit edilemeyen dalga fazları da gözlemlenebilir. Mikrotremor dizilim ölçümleri, kesme dalgası hızının (Vs) derinlikle değişimini temsil eden bir boyutlu hız profillerinin elde edilmesinde yaygın olarak kullanılmaktadır. Bu amaçla farklı dizilim geometrileri ve çeşitli pasif yüzey dalgası yöntemleri giderek daha fazla tercih edilmektedir. Zemin tabakalarının yatay olduğu ve ortam gürültüsünün ağırlıklı olarak yüzey dalgalarından oluştuğu varsayımı altında, dizilim ölçümleri yüzey dalgalarına ait dispersiyon eğrilerinin çıkarılmasını sağlar. Çözünürlük ve aliasing sınırları dikkate alınarak seçilen otokorelasyon eğrisinden uygun dispersiyon eğrisi belirlenir ve bu eğri sığ kesme dalgası hızlarının ters çözümü için kullanılır. Yöntem temel olarak dispersiyon eğrilerinin ters çözümüne ve uzaysal özilişki yaklaşımına dayanmaktadır. Bu çalışmanın odak noktası, uygulamada kritik öneme sahip dizilim geometrisinin performansının değerlendirilmesidir. Aynı lokasyonda ve aynı açılım mesafelerinde kurulan beş farklı dizilim tipi karşılaştırılmış, etki derinliği, duyarlılık ve uygulama kolaylığı açısından ortaya çıkan farklar tartışılmıştır. Elde edilen sonuçlar genel olarak tutarlıdır. Eşkenar üçgen ve artı biçimli dizilimler düşük frekans bilgisini daha iyi yakalarken, daha uzun açılımlar derin birimlere karşılık gelen düşük frekans hız değerlerinin elde edilmesini sağlamıştır.

Anahtar Kelimeler

• Uzaysal özilişki (SPAC)
• mikrotremor
• s-dalgası
• dizilim geometrisi
• dispersiyon

Comparison of Spatial Autocorrelation Calculation Methods with Different Geometric Arrangements for Rayleigh Wave Dispersion Curve Estimation

Öz

Geometrically arrayed ambient noise measurements are an effective method for determining the dynamic properties of near-surface geological units, and by combining station records, they increase the signal-to-noise ratio, providing significant advantages for studies conducted in urban areas. In this way, wave phases that cannot be detected with a single station can also be observed. Microtremor array measurements are widely used to obtain one-dimensional shear-wave velocity profiles (Vs) representing the variation of shear-wave velocity with depth. For this purpose, different array geometries and various passive surface-wave methods are increasingly preferred. Assuming that soil layers are horizontally stratified and ambient noise is predominantly composed of surface waves, array measurements enable the extraction of surface-wave dispersion curves. Taking into account resolution and aliasing limits, a suitable dispersion curve is selected from the autocorrelation curve, and this curve is used for inversion of shallow shear-wave velocities. The method is essentially based on the inversion of dispersion curves and the spatial autocorrelation approach. The focus of this study is to evaluate the performance of array geometry, which is critically important in practice. Five different array types established at the same location and with the same aperture distances were compared, and the resulting differences in terms of investigation depth, sensitivity, and ease of application were discussed. The obtained results are generally consistent. Equilateral-triangle and cross-shaped arrays capture low-frequency information better, while longer apertures provide velocity values at low frequencies corresponding to deeper units.

Anahtar Kelimeler

• Spatial autocorrelation (SPAC)
• microtremor
• s-wave
• array geometry
• dispersion

Kaynakça

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