Late Cenozoic stress states around the Bolu Basin along the North Anatolian Fault, NW Turkey |
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| Authors: | Suha Ozden Semir Over Kaan Sevki Kavak Serife Sevinc Inal |
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| Institution: | aDepartment of Geological Engineering, Canakkale Onsekiz Mart University, 17020 Canakkale, Turkey;bDepartment of Geophysical Engineering, Mustafa Kemal University, 31040 Antakya, Turkey;cDepartment of Geological Engineering, Cumhuriyet University, 58140 Sivas, Turkey;dDil Devrimi Caddesi, Akkonaklar Sitesi, B8-88, No. 28, Eryaman Evleri, Etimesgut, Ankara, Turkey |
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| Abstract: | This study defines the Late Cenozoic stress regimes acting around the Bolu Basin along the North Anatolian Fault in northwestern Turkey. The inferred regional stress regime, obtained from the inversion of measured fault-slip vectors as well as focal mechanism solutions, is significant and induces the right-lateral displacement of the North Anatolian Fault. The field observations have also revealed extensional structures in and around the Bolu Basin. These extensional structures can be interpreted as either a local effect of the regional transtensional stress regime or as the result of the interaction of the fault geometries of the dextral Duzce Fault and the southern escarpment of the North Anatolian Fault, bordering the Bolu Basin in the north and in the south, respectively.The inversion of slip vectors measured on fault planes indicates that a strike-slip stress regime with consistent NW- and NE-trending σHmax(σ1) and σHmin(σ3) axes is dominant. Stress ratio (R) values provided by inversion of slip vectors measured on both major and minor faults and field observations show significant variations of principal stress magnitudes within the strike-slip stress regime resulting in older transpression to younger transtension. These two stress states, producing dextral displacement along NAF, are coaxial with a consistent NE-trending σ3 axis. The earthquake focal mechanism inversions confirm that the transtensional stress regime has continued into recent times, having identical horizontal stress axis directions, characterized by NW and NE-trending σ1 and σ3 axes, respectively. A locally consistent NE-trending extensional, normal faulting regime is also seen in the Bolu Basin. The stress-tensor change within the strike-slip stress regime can be explained by variations in horizontal stress magnitudes that probably occurred in Quaternary times as a result of the westward extrusion of the Anatolian block. |
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| Keywords: | Fault-slip vector Inversion Late Cenozoic Stress states Transtensional Bolu Basin North Anatolian Fault |
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