Investigating the Correlation Between the High-Frequency Spectral Attenuation Parameter Kappa and Vs30 in the Central Aegean Region

Abstract

The Aegean Region has a high risk of seismic activity because of its active fault lines and dense population. To assess this risk accurately, it is essential to understand the high-frequency spectral decay parameter known as "kappa" (κ), which reflects local site conditions. In this study, 1056 records of 291 earthquakes collected from 43 stations in the Central Aegean Region, connected to the Turkish National Strong Ground Motion (TR-KYH) Observation Network operated by AFAD, with known Vs30 (average shear-wave velocity in the top 30 meters) values, were used. Using the Central Aegean subset of a large dataset compiled for Western Anatolia, a regional κ model was created, incorporating site-specific κ values for various site classes and a common distance dependence. The site-specific attenuation parameter (κ0) for each station was then calculated by removing the regional attenuation effect. An analysis of the spatial distribution of κ0 and Vs30 values shows that alluvial sites in the Aegean basins usually have high κ0 and low Vs30 values. In contrast, stiff soil and rock sites near the horst structures exhibit lower κ0 and higher Vs30 values. The results indicate a general negative correlation between κ0 and Vs30, despite significant scatter. This finding suggests that κ0 could potentially be used as a proxy for site classification at sites where Vs30 values are unknown. However, further research with larger datasets representing a wider range of site classes is necessary to find a more reliable and significant relationship between these two parameters. Validation of such a relationship would facilitate the widespread use of κ0 in earthquake engineering applications.

Keywords

• High-frequency Spectral Attenuation
• Site Classification
• Vs30 Velocity
• Central Aegean Region

Orta Ege'de Yüksek Frekanslı Spektral Sönümleme Parametresi Kappa ile Vs30 Arasındaki İlişkinin Araştırılması

Abstract

Aktif fay hatları ve yoğun nüfusu nedeniyle Ege Bölgesi yüksek deprem riski taşımaktadır. Bu riskin doğru şekilde değerlendirilmesinde, yerel zemin koşullarını yansıtan yüksek frekanslı spektral sönümleme katsayısının ("kappa", ) bilinmesi kritik öneme sahiptir. Bu çalışmada, AFAD tarafından işletilen Türkiye Ulusal Kuvvetli Yer Hareketi (TR-KYH) Gözlem Ağı’na bağlı, Orta Ege Bölgesi’nde yer alan ve Vs30 (ilk 30 m’deki ortalama kayma dalgası hızı) değerleri bilinen 43 istasyonda kaydedilmiş 291 depreme ait 1056 adet kayıt kullanılmıştır. Batı Anadolu için daha önce derlenmiş geniş bir veri setinin Orta Ege Bölgesi'ni temsil eden alt grubu kullanılarak, çalışma sahasındaki zemin sınıflarına özgü κ değerlerini ve ortak bir uzaklık bağımlılığını içeren bölgesel bir κ modeli geliştirilmiştir. Ardından, bölgesel sönümleme etkisi arındırılarak her bir istasyona özgü yerel sönümleme parametresi (0) hesaplanmıştır. 0 ve Vs30 değerlerinin mekansal dağılımı incelendiğinde, Ege havzalarındaki alüvyon zeminlerin genellikle yüksek 0 ve düşük Vs30 değerlerine sahip olduğu; buna karşın bölgesel horst yapılarına yakın sıkı zemin ve kayaçların ise daha düşük 0 ve daha yüksek Vs30 değerleri sergilediği görülmektedir. Sonuçlar, κ0 ile Vs30 arasında belirgin bir saçılım gözlense de genel olarak negatif bir korelasyonun varlığına işaret etmektedir. Bu bulgu, Vs30 değerinin bilinmediği sahalarda κ0’ın potansiyel bir zemin sınıflandırma parametresi olarak kullanılabileceğini göstermektedir. Ancak iki parametre arasında daha güvenilir ve anlamlı bir ilişki kurabilmek için farklı zemin gruplarını temsil eden daha kapsamlı veri setleriyle çalışmaların derinleştirilmesi şarttır. Böyle bir ilişkinin doğrulanması, κ₀'ın deprem mühendisliği uygulamalarında yaygın kullanımının önünü açacaktır.

Keywords

• Yüksek Frekanslı Spektral Sönümleme
• Zemin Sınıflandırması
• Vs30 Hızı
• Orta Ege Bölgesi

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