14:15 〜 14:30
[SEM12-13] Brittle-Ductile Characteristics of the North Anatolian Fault Zone by Magnetotelluric Method and Other Geophysical Parameters
★Invited Papers
キーワード：North Anatolian Fault Zone, Magnetotellurics, Brittle-ductile transition, Locking depth
The North Anatolian Fault Zone (NAFZ) is a large-scale transform plate boundary located between the Anatolian and Eurasian plates. The northward movement of the Arabian plate relative to the stable Eurasian plate and the subduction of the African plate beneath the Anatolian plate have caused the Anatolian block to move westward along the NAFZ and the East Anatolian Fault Zone with right- and left-lateral strike-slip faulting mechanisms, respectively. The 1600 km long NAFZ runs almost parallel to the Black Sea coast for most of its length as a single branch and branches off in the Marmara region in northwestern Türkiye. During the last century, the NAFZ has hosted many large earthquakes (Mw > 6.7) indicating a high seismic potential of the region. Therefore, a better understanding of the depth extension of the brittle to ductile zone becomes important for seismic hazard assessment as it controls the energy released along fault zones and the magnitude of earthquakes.
The brittle to ductile transition zone (BDTZ) represents the variation in strength of the earth’s material with increasing depth and temperature. The material is at low temperatures and shows the ability to fail in brittle form accompanied by earthquakes at shallow depths. Its strength increases with depth down to the BDTZ, where increased temperature weakens the strength of the material leading to slip below this depth and the material is considered ductile. The presence of fluid can affect the mechanical strength of rocks and if the fluid has an interconnected network, its effect increases dramatically. The magnetotelluric (MT) method, a passive electromagnetic method, can effectively detect the regions of interconnected fluid at the crustal and upper mantle scale and can indicate the transition from brittle to ductile zones.
In the current work we investigate the brittle-ductile transition zones by combining magnetotelluric models along the NAFZ with other geophysical parameters collected in the region. The NAFZ is generally characterised by a deep zone of high conductivity bounded by resistive zones to the north and south. This conductive structure is attributed to fluids within a highly fractured damage zone and extends to depths of tens of kilometres. In the magnetotelluric profiles crossing the fault, the change in electrical resistivity from the highly resistive to the relatively conductive zone is indicative of the BDTZs. The depth extend of the BDTZ confirms the locking depths inferred from geophysical and geodetic constraints in the region and correlates well with the westward thinning of the crust.
The brittle to ductile transition zone (BDTZ) represents the variation in strength of the earth’s material with increasing depth and temperature. The material is at low temperatures and shows the ability to fail in brittle form accompanied by earthquakes at shallow depths. Its strength increases with depth down to the BDTZ, where increased temperature weakens the strength of the material leading to slip below this depth and the material is considered ductile. The presence of fluid can affect the mechanical strength of rocks and if the fluid has an interconnected network, its effect increases dramatically. The magnetotelluric (MT) method, a passive electromagnetic method, can effectively detect the regions of interconnected fluid at the crustal and upper mantle scale and can indicate the transition from brittle to ductile zones.
In the current work we investigate the brittle-ductile transition zones by combining magnetotelluric models along the NAFZ with other geophysical parameters collected in the region. The NAFZ is generally characterised by a deep zone of high conductivity bounded by resistive zones to the north and south. This conductive structure is attributed to fluids within a highly fractured damage zone and extends to depths of tens of kilometres. In the magnetotelluric profiles crossing the fault, the change in electrical resistivity from the highly resistive to the relatively conductive zone is indicative of the BDTZs. The depth extend of the BDTZ confirms the locking depths inferred from geophysical and geodetic constraints in the region and correlates well with the westward thinning of the crust.