An Investigation on the Crustal Velocity Variations of the North Anatolian Fault Zone by a Dense Seismic Array

Abstract

Asymmetrical distribution of microfractures across the fault is the result of repeated occurrence of earthquakes on active fault zones. Earthquake sequences generate bimaterial interfaces which separate elastically different materials from each other and provide important implications for earthquake behavior. Dense Array of Northern Anatolia (DANA) network provides valuable data in order to investigate bimaterial interface across the north and south branches of North Anatolian Fault Zone (NAFZ) beneath Sakarya-Sapanca segments. The aim of this study is to determine velocity contrast along the north and south branches of NAFZ by using the dense temporary seismic DANA network along the western edge of NAFZ between Sakarya and Sapanca segments From May 2012 to September 2013, more than 50.000 waveforms are compiled from 109 teleseismic earthquakes and 73 stations of DANA temporary network operated in the study area. We used differences between arrival times to detect and quantify velocity contrast in crust across the fault. Although local changes in velocity ratios were found in reference station analyzes, overall velocity differences were observed beneath north of the NAFZ northern branch and relatively east and southeast of the NAFZ northern branch. It is possible to mention the presence of a two-material interface between the two branches of the fault. The results indicate the existence of biomaterial interface along the NAFZ branches which provides important implications for understanding the earthquake dynamics and mechanism.  

Keywords

• Bi-material Interface,velocity contrast,North Anatolian Fault Zone,Sakarya-Sapanca Segment,Turkey

Kuzey Anadolu Fay Zonu’nun Kabuk Hızı Değişimlerinin Yoğun Sismik Dizilim ile İncelenmesi

Abstract

Aktif fay zonları boyunca asimetrik olarak dağılmış olan mikro çatlaklar bu zonlardaki depremlerin tekrarlı oluşumları nedeniyle meydana gelmektedir. Aynı bölgede sürekli tekrarlanan depremler, elastik olarak farklı olan malzemeleri ayırarak iki-malzemeli arayüzeyler meydana getirir ve deprem davranışını etkileyen önemli sonuçlar doğurur. Kuzey Anadolu Fay Zonu üzerinde kurulan DANA (Dense Array of Northern Anatolia) sismik ağı Kuzey Anadolu Fay Zonu’nun Sakarya ve Sapanca segmentleri üzerinde iki malzemeli arayüzeyin incelenmesi için elverişli veri sağlamaktadır. Bu çalışmanın amacı, yoğun sismik dizilim bulunan Kuzey Anadolu Fay Zonu’nun (KAFZ) batı ucunda Sakarya ve Sapanca segmentleri arasında, deprem dalgası çapraz ilişki analizleri kullanarak, iki malzemeli arayüzey geçişindeki hız değişimlerini belirlemektir. Araştırma kapsamında 2012-2013 yıllarında, çalışma alanında faaliyet gösteren DANA geçici sismik ağına ait 73 adet sismik istasyondan, 109 adet uzak deprem kaydı kullanılarak 50.000'den fazla dalga formu derlenmiştir. Uzak deprem dalgalarının, sismik kayıtçılara varışları arasındaki zaman farkları, fayın karşılıklı bölümlerinde kabuktaki hız kontrastını tespit etmek ve fark değerini ölçmek için kullanılmıştır. Elde edilen bulgular KAFZ kuzey kolunun kuzeybatısında düşük, kollar arası Armutlu-Ovacık bloğu altında yüksek hızlara işaret etmektedir. Referans kayıtçıların analizinde, hız oranlarında lokal değişimler hesaplanmış olsa da, bölge geneline bakıldığında KAFZ kuzey kolunun kuzeyi ile, yine KAFZ kuzey kolunun doğusu ve güney doğusu arasında görece büyük hız farkları elde edilmiştir. Sonuçlar, KAFZ kuzey ve güney kollarındaki hız değişimlerini ve genel tektonik ortamla ilişkilendirilen özellikleri ortaya koymaktadır.

Keywords

• iki malzemeli arayüzey,hız farkı,Kuzey Anadolu Fay Zonu,Sakarya-Sapanca Segmenti,Türkiye

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