Geology of the North Bozgush Fault Zone and Its Tectonic Significance, NW Iran

Year 2013, Volume: 34 Issue: 2, 141 - 168, 01.03.2013

Reza Saber Veysel Işık Ayşe Çağlayan

Abstract

NW Iran, including the study area is one of the seismically active regions between Zagros Thrust Belt at the south and Caucasus at the north. In this region, an area known as Alborz-Azerbaijan zone includes many significant active fault zones. Not only large magnitude historical earthquakes (Ms>7), but also 1997 Ardebil (Mw 6.1) and 2012 Ahar-Varzagan (Mw 6.4) earthquakes reveal that the region is seismically active. The North Bozgush Fault Zone in this region has tens of kilometers in length and hundreds of meters in width. The zone has produced some large and destructive earthquakes.In this study five different study domains have been chosen along the North Bozgush Fault Zone. These are Sherbian, Danbaran, Anakiz, Damencan and Abgerm regions, respectively. The North Bozgush Fault Zone affects the Cenozoic units. Along this zone Eocene units thrusted over Miocene and/or Plio-Quaternary sedimentary units. The zone is mainly characterized by strike-slip faults with reverse component and reverse faults. Reverse faults striking N55o-85oE and dip of 40o-50o to the SW while strike-slip faults show right lateral slip with N50o-85oW and N60o-80oE directions.Our structural data analysis indicates that the North Bozgush Fault Zone shows σ1 principal stress (compression) with NW-SE direction and σ3 principal stress (extension) with NE-SW direction. The axis direction of σ2 principal stress is vertical and the stress ratio (R) is 0.12. These results suggest that the tectonic regime along the North Bozgush Fault Zone is transpressive. Fault slip analysis results are compatible with stress directions and GPS velocity results for NW Iran. Western part of the Bozgush Mountains is bounded with the Tabriz Fault Zone. Our field studies suggest that there is a genetic relationship between the North Bozgush Fault Zone and the Tabriz Fault Zone

Keywords

Structural analysis, North Bozgush Fault Zone, Tabriz Fault Zone, NW Iran

Kuzey Bozkuş Fay Zonunun (KB İran) Jeolojisi ve Tektonik Önemi

Abstract

İnceleme alanının yer aldığı KB İran, kuzeyde Kafkaslar güneyde Zagros Bindirme Kuşağı arasında yer alan sismik bölgelerden biridir. Bölgede Elborz-Azerbaycan Zonu olarak adlanan alan içerisinde aktivitesini sürdüren önemli fay zonları bulunmaktadır. Meydana gelen büyük tarihsel depremler (Ms>7) yanında 1997 Erdebil (Mw 6.1) ve 2012 Eher-Verzegan (Mw 6.4) depremleri bölgenin sismik aktivitesini ortaya koymaktadır. Bölge içerisinde yer alan Kuzey Bozkuş Fay Zonu onlarca kilometre uzunluğa ve yüzlerce metre genişliğe sahiptir. Zon, içerisinde oluşmuş tarihsel büyük depremler kayıtlarda yer almaktadır.Bu çalışmada Kuzey Bozkuş Fay Zonu 5 farklı alanda (Şerbiyan, Danbaran, Anakız, Damencan ve Abgerm bölgeleri) incelenmiştir. Kuzey Bozkuş Fay Zonu Senozoyik yaşlı litolojileri etkilemiş olup fay boyunca Eosen yaşlı birimler Miyosen ve/veya Pliyo-Kuvaterner çökel kayalar üzerine itilmiştir. Zon içerisindeki faylar egemen olarak ters bileşenli doğrultu atımlı ve ters faylar ile temsil olur. Ters faylar K55o-85oD, 40o-50oGB durumludur. Doğrultu atımlı faylar ise K50o-85oB ve K60o-80oD doğrultularda ve sağ yanal karakterdedir.Yapısal verilerin analizi Kuzey Bozkuş Fay Zonunun KB-GD σ1 (sıkışma) ve KD-GB σ3 (genişleme/gerilme) ana stres doğrultularına sahip olduğunu ortaya koyar. σ2 ana stres ekseni düşey konumda ve R değeri 0.12 dir. Bu sonuçlar KBFZ’de etkin tektonik rejimin yanal sıkışmalı olduğuna işaret eder. Fay kayma analiz sonuçları KB İran için önerilen stres yönelimi ve GPS çalışmalarından elde edilen sonuçlarla uyumludur. Bozkuş Dağları’nın batı kesimi Tebriz Fay Zonu ile sınırlanır. Arazi gözlemleri Tebriz Fay Zonu’nun bu çalışmaya konu olan Kuzey Bozkuş Fay Zonu ile kökensel ilişkili olduğunu ortaya koyar

Keywords

Yapısal analiz, Kuzey Bozkuş Fay Zonu, Tebriz Fay Zonu, KB İran

References

• Abdollahi, S., Mohajjel, M., Salagi, A., and Tag- hipour, K., 2012. Compressional termi- nation of North Tabriz Fault in Bozkush mountains, 30th GSI congress, Iran, 7.
• Afshar-Harb, A., 1970. Geology of Sarakhs area and Khangiran gas field. Bulletin of the Iranian Petroleum Institute, 37, 86-96.
• Aghanabati, A., 2004. Geology of Iran. Geologi- cal Survey of Iran Pub., 707 p.
• Alavi, M., 1972. Etude géologique de la région de Djam. Geological Survey of Iran, Re- ports, 23, 1-288.
• Alavi, M., 1977. Geology and petrology in the ophiolite range NW of Sabzevar (Kho- rassn, Iran). Geol. Soc. of Iran , No. 43, 147.
• Alavi, M., 1991a. Tectonic map of the Middle East. Geological Survey of Iran, Tehran.
• Alavi, M., 1991b. Sedimentary and structural characteristics of the Paleo-Tethys remnants in northeastern Iran. Geolo- gical Society of American Bulletin, 103, 983-992.
• Alavi, M., 1994. Tectonics of the Zagros oroge- nic belt of Iran: New data and interpre- tations. Tectonophysics, 229, 211-238.
• Allen, M., Jackson, J., and Walker, R., 2004. Late Cenozoic reorganization of the Arabia–Eurasia collision and the com- parison of short-term and long-term deformation rates. Tectonics, 23, no. 2,
• TC2008, doi: 10.1029/2003TC001530.
• Ambraseys, N.N., and Melville, C.P., 1982. A History of Persian Earthquakes, Camb- ridge University Press, New York, 240.
• Berberian, M., 1997. Seismic sources of the
• Transcaucasian historical earthquakes,
• Historical and Prehistorical Earthqua
• kes in the Caucasus, D. Giardini and S.
• Balassanian (Editors), NATAO Asi Se
• ries Environment, Kluwer Academic
• Press, the Netherlands, 28, 233-311.
• Berberian, M., and Arshadi, S., 1976. On the Evidence of the Youngest Activity of the North Tabriz Fault and the Seis- micity of Tabriz City. In: Contribution to the Seismotectonics of Iran, Part II (ed. M. Berberian). Geol. Surv. Iran, 39, 397-418.
• Berberian, M., and King, G.C.P., 1981. Towards a paleogeography and tectonic evolu- tion of Iran: Canadian Journal of Earth Science, 18, 210-265.
• Berberian, M., and Yeats, R.S., 1999. Patterns of historical earthquake rupture in the Iranian Plateau. Bull. Seismol. Soc. Am., 89, 120–139.
• Copley, A., and Jackson, J., 2006. Active tec- tonics of the Turkish–Iranian Plateau.
• Tectonics 25, TC 6006.
• Darvishzadeh, A., 1991. Geology of Iran. Da- nesh-Emruz Pub., Tehran, 901p.
• Djamour, Y. Vernant, P., Nankali, H., and Tava