Reconstructing the deformation of the North Anatolian Fault Zone through restoring the Oligo–Miocene exhumation pattern of the Almacık Block (northwestern Turkey) based on the apatite (U–Th)/He ages

The Almacık Block is an approximately 73 km long and 21 km wide tectonic sliver formed by the North Anatolian Fault Zone in northwestern Turkey. Morphologically, it is one of the most pronounced structures along the North Anatolian Fault Zone. All the segments bounding the Almacık Block were ruptured during the second half of the 20th century. The fifty-four apatite (U–Th)/He ages we obtained showed that the region including the Almacık Block was exhumed during the Oligo–Miocene interval and then original exhumation pattern was distorted by the North Anatolian Fault Zone during the Miocene to recent. To interpret this distortion and to reconstruct it to the original state, we modelled “Λ”-shaped mountain fronts in the most probable deformation scenarios. The block has been tilted southward about an approximately east–west-trending horizontal (slightly dipping to the east) axis. As a result of this rotation, the northern part of the block has been uplifted about 2800 m, whereas the southern part has subsided about 430 m, likely during the last 2.5 Myr. The exhumation in the studied region started at around 34 Ma and lasted until 16 Ma with a mean exhumation rate of about 60 m/Myr.

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Seismotectonic setting at the North Anatolian Fault Zone after the 1999 Mw=7.4 Izmit earthquake based on high-resolution aftershock locations

Advances in Geosciences ◽

10.5194/adgeo-14-85-2008 ◽

2008 ◽

Vol 14 ◽

pp. 85-92 ◽

Cited By ~ 4

Author(s):

M. Bohnhoff ◽

F. Bulut ◽

E. Görgün ◽

C. Milkereit ◽

G. Dresen

Keyword(s):

High Resolution ◽

Fault Zone ◽

Wide Band ◽

North Anatolian Fault ◽

Double Difference ◽

North Anatolian Fault Zone ◽

Coseismic Slip ◽

The North ◽

Northwestern Turkey ◽

Better Than

Abstract. The most recent devastating earthquakes that occurred along the North Anatolian Fault Zone (NAFZ) in northwestern Turkey were the 1999 Izmit (Mw=7.4) and Düzce (Mw=7.1) events. In this study we present a catalog of Izmit aftershock hypocenters that was deduced from a network covering the entire 140 km long rupture of the mainshock. 7348 events with a location accuracy better than 5 km are analysed. Aftershocks were observed along the entire ruptured segment along a 20 km wide band of activity. Events are clustered in distinct regions and dominantly occur at 5 to 15 km depth. The eastern termination of the Izmit rupture is characterized by a sharp and steeply dipping boundary exactly where the Düzce mainshock initiated 87 days after the Izmit event. Relocation of the events using double-difference technology results in 4696 high-resolution hypocenters that allow resolving the internal structure of the seismically active areas with a resolution of 300 m (horizontal) and 400m (vertical). Below the Akyazi Plain, representing a small pull-apart structure at a triple junction of the NAFZ, we identify planes of activity that can be correlated with nodal planes of EW extensional normal faulting aftershocks. Along the easternmost Karadere-Düzce segment we identify the down-dip extension of the Karadere fault that hosted about 1 m of right-lateral coseismic slip. At the easternmost rupture we correlate a cloud-type distribution of seismic activity with the largest aftershocks in this area, a subevent of the Izmit mainshock and the Düzce mainshock that all have an almost identical focal mechanism. This part of the NAFZ is interpreted as a classical example of a seismic barrier along the fault.

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