Fault zone conductors in Northwest Turkey inferred from audio frequency magnetotellurics

Abstract

A comparison of the electrical properties of the two main branches of the North Anatolian Fault is made based on audio-frequency magnetotelluric (AMT) surveys carried out along three typical pro les across the North Anatolian Fault Zone (NAFZ). These two branches are (i) the active northern branch (Izmit-Adapazar Fault (IAF)) where the 17 August, 1999, Izmit earthquake took place, and (ii) the less active southern branch (IznikMekece Fault (IMF)). In this paper, we focus on the shallow depths (surface-1.5 km) in search for conductors near the fault zone for the purpose of comparing these two branches with each other, as well as other strike-slip faults. Phase tensor analyses and Groom-Bailey decompositions were applied to check the dimensionality of the AMT data. Following the tensor analyses and decompositions, two-dimensional inversions were carried out to yield models based on the transverse electric (TE), and transverse magnetic (TM), modes. These models suggest that the North Anatolian Fault exhibits signs of fault zone conductors (FZC) regardless of being active or less active.

Electrical characterization of the North Anatolian Fault Zone underneath the Marmara Sea, Turkey by ocean bottom magnetotellurics

“…All of these tectonic zones form constituent parts of the Western Pontides, a series of east-west trending Tethyan orogenic belts; this means that all three zones keep almost the entire evolutionary record of the Tethysides (Yılmaz et al 1997). The occurrence of the İzmit and Düzce earthquakes on the northern side of these tectonic zones (Tank et al 2003(Tank et al , 2005Kaya et al 2009;Tank 2012) indicates the significance of the extension of these zones into the Marmara Sea, in terms of possible locations for the next devastating earthquake along the NAF.…”

Electrical resistivity structure at the North-Central Turkey inferred from three-dimensional magnetotellurics

“…Analogously, lack of fluids in the vicinity of faults can infer to near hydrostatic pore pressures that may lead to longer times of stress accumulation and larger rupture events. Previously, MT measurements made on locked strikeslip faults demonstrated a characteristic portrayed by the presence of resistive bodies at both sides of the fault (e.g., Unsworth et al 1999;Goto et al 2005;Tank et al 2003;Tank 2012;Karaş et al 2017). Both the metamorphic units of CPS (R 2 ) and mafic units south of the NAF (R 1 ) can be interpreted as reasonable geological bodies to resist such inclusion of fluids due to their low porosity values or poor interconnection between their pores.…”

Electrical conductivity of a locked fault: investigation of the Ganos segment of the North Anatolian Fault using three-dimensional magnetotellurics

“…Considering that this zone was also marked as the maximum rupture of the 1912 Mürefte Earthquake (Aksoy et al 2010;Meghraoui et al 2012), further geological discussion is required to improve the understanding of the importance of this relatively large conductive area. Tank (2012) compared the FZCs of the seismically active İzmit-Adapazari Fault (IAF) and İznik-Mekece Fault (IMF), representing seismic gaps. Although both faults share the same fluid source in the seismogenic zone (Tank et al 2005), the shallow structure has different attributes, which are associated with the seismicity and related deformation.…”

“…Multiple MT studies were performed aiming to image electrical resistivity structures along the NAF (Honkura et al 2000Oshiman et al 2002;Tank et al 2003Tank et al , 2005Tank 2012;Türkoğlu et al 2008;Kaya et al 2009Kaya et al , 2013. In this study, the first magnetotelluric data that specifically focus on the Ganos Region were analyzed with three-dimensional numerical modeling routines.…”