Kuzey Anadolu Fay Zonu' nun orta ve batı kesiminde bölgesel gerilme durumunun incelenmesi

Bu makalede, Kuzey Anadolu Fay Zonu'nun orta kesimi ile batı kesiminde (Marmara'nın doğusuna kadar) egemen olan gerilme tensörünün durumu, fay toplulukları ve deprem odak çözüm mekanizmaları kullanılarak incelenmiştir. Kinematik analiz, bölgede egemen olan tektonik rejimin transpresiften transtensife dönüştüğünü göstermektedir. Sağ yanal doğrultu alımlı olan her iki rejim için elde edilen en büyük yatay gerilme $sigma hmax (sigma_1)$ ve en küçük yatay gerilme $sigma hmax (sigma_3)$ doğrultulan aynıdır ve KB-GD ve KD-GB. Ancak hesaplanan ortalama gerilme oranı R farklıdır. Transpresif rejim için Rort= 0.75 ve transtensif rejim için Rort= 0.24 tür. Bu değişim Erken-Orta Pleyistosen'de gerçekleşmiştir. Deprem odak çözümlerinin ters çözüm işlemi, KB-GD (N126°E) doğrultulu 0, ve KD-GB (N217°E) doğrultulu $sigma_3$ eksenleri, ile R= 0.40 değerini vermektedir. Hesaplanan R değeri çalışma bölgesinde günümüzde egemen olan gerilme rejiminin transtensif olduğunu göstermektedir. Batıdaki ile doğudaki levha kenarlarındaki kuvvetlerin farklı etkimesi, gerilme rejimindeki değişimin nedeni olabilir. Kinematik analiz sonucunda ortaya konan gerilme durumundaki zamansal değişimler, özellikle Ege yitim zonundaki gerilme rejimlerinde meydana gelen değişimlerin etkisi altındadır.

Regional stress state analysis in central and occidental parts of the North Anatolian Fault Zone

This paper concerns the determination of stress tensor from a set of striated faults and of focal mechanisms of earthquakes. The central and occidental parts of the North Anatolian Fault Zone illustrates the applied methodology. Then, temporal changes in tectonic regimes of the central North Anatolian Fault Zone are briefly examined. The fault kinematics analysis within central North Anatolian Fault shows that strike-slip stress changes from transpressional regime to transtensional regime as indicated by chronologies of fault slip vectors. Both states have consistent NW- and NE- trending $sigma_1$ and $sigma_3$ axes respectively, but have significantly different mean R values: Rm=0.75 for transpressional and Rm=0.24 for transtensional regimes respectively. The inversion of focal mechanisms, occurred in the central and occidental parts of North Anatolian Fault Zone, shows that actual stress rejime is transtensional and is characterized by a NW-(N126°E) trending 0, and a NE-(N217E) trending $sigma_3$ axes with a R value of 0.40. The stress changes along the North Anatolian Fault Zone result from the coeval influence of forces acting in the west and in the east. However, the timing of the temporal stress change permits to suggest that Quaternary stress regime variation in central North Anatolian Fault Zone is mainly due to the Aegean domain influence.

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