Moment Tensor Analysis and Stress Analysis of Microearthquakes Occurred Between Ganos Fault and Tekirdag Basin

Abstract

In this study, moment tensor analyses of microearthquakes recorded with the MONGAN-1 and MONGAN-2 seismic networks deployed on the Ganos Fault are done. The MONGAN-1 seismic network consists of 40 short-period stations located in a local area of approximately 10 km2, and the general feature of the earthquakes used is that they are out of the network. The effect of the azimuthal coverage of the seismic network, behaving like a point receiver covering a narrow azimuthal range for moment tensor analysis of microearthquakes, is investigated. For this purpose, 61 microearthquakes with magnitudes varying between 1.5≤Mw≤3.7, occurred between October 2017 and June 2020 in the region between Tekirdağ Basin and Ganos Fault, are analyzed. Broadband national network records of 10 earthquakes with magnitudes ranging between 2.8≤Mw≤3.7 are used to determine the focal mechanisms using both moment tensor inversion and P wave first motion polarities techniques and then are compared with the MONGAN network’s solutions. Although there are minor differences in the strike, dip and rake angles of the focal mechanisms obtained, it is observed that the three focal mechanism analysis results are generally compatible with each other. Although the azimuthal coverage of the seismic network is not good, moment tensor inversions of the microearthquakes can be successfully applied with an accurate crustal model. As a result of the stress analysis, the principal stress axes orientations of σ1, σ2 and σ3 are obtained as 277.2/42.8, 87.7/46.7 and 182.9/4.7 (azimuth/dip), respectively. The stress ratio in the region is calculated as 0.60.

Keywords

• Microearthquake
• Moment Tensor Inversion
• Stress Tensor Inversion
• Ganos Fault
• ISOLA CMT Software

Ganos Fayı ile Tekirdağ Baseni Arasında Meydana Gelen Mikro Depremlerin Moment Tensör ve Gerilme Analizleri

Abstract

Bu çalışmada Ganos Fayı üzerinde kurulu MONGAN-1 ve MONGAN-2 sismik ağları ile kaydedilen mikro depremlerin moment tensör ve gerilme analizleri yapılmıştır. MONGAN-1 sismik ağı yaklaşık 10 km2’lik lokal bir alanda kurulu 40 adet kısa periyot deprem istasyonundan oluşur ve kullanılan depremlerin genel özelliği ağ dışı depremler olmalarıdır. Bu nedenle dar bir azimut aralığında adeta bir nokta alıcı gibi davranan sismik ağa ait kayıtlar kullanılarak azimutal dağılımın çözümler üzerindeki etkisi araştırılmıştır. Seçilen depremler Tekirdağ Baseni ile Ganos Fayı arasında kalan bölgede, Ekim 2017-Haziran 2020 tarihleri arasında meydana gelen, büyüklüğü 1.5≤Mw≤3.7 arasında değişen 61 adet mikro depremden oluşur. Depremlerden büyüklüğü 2.8≤ Mw≤3.7 arasında değişen 10 tanesinin geniş bant ulusal ağ kayıtları kullanılarak hem moment tensör hem de P dalgası ilk hareket yönlerinden odak mekanizmaları belirlenerek MONGAN ağı çözümleri ile karşılaştırılmıştır. Elde edilen odak mekanizmalarının doğrultu, eğim ve atım açılarında küçük farklar olsa da genellikle her deprem için elde edilen üç odak mekanizmasının da birbirleriyle uyumlu olduğu görülmüştür. Bölgedeki hız yapısını yüksek çözünürlüklü olarak temsil eden bir kabuk modeli ile azimutal dağılımın iyi olmadığı istasyon kayıtlarıyla mikro depremlerin moment tensör analizlerinin başarıyla uygulanabileceği görülmüştür. Gerilme analizi sonucunda σ1, σ2 ve σ3 asal gerilme eksenlerinin konumu sırasıyla 277.2/42.8, 87.7/46.7 ve 182.9/4.7 (azimut/dalım) olarak bulunmuştur. Bölgedeki gerilme oranı ise 0.60 olarak hesaplanmıştır.

Keywords

• Mikro Deprem
• Moment Tensör Analizi
• Gerilme Analizi
• Ganos Fayı
• ISOLA

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