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Advances in Geosciences An open-access journal for refereed proceedings and special publications

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Adv. Geosci., 14, 85-92, 2008
https://doi.org/10.5194/adgeo-14-85-2008
© Author(s) 2008. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.
 
02 Jan 2008
Seismotectonic setting at the North Anatolian Fault Zone after the 1999 Mw=7.4 Izmit earthquake based on high-resolution aftershock locations
M. Bohnhoff, F. Bulut, E. Görgün, C. Milkereit, and G. Dresen GeoForschungsZentrum Potsdam, Telegrafenberg D424, 14473 Potsdam, Germany
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.

Citation: Bohnhoff, M., Bulut, F., Görgün, E., Milkereit, C., and Dresen, G.: Seismotectonic setting at the North Anatolian Fault Zone after the 1999 Mw=7.4 Izmit earthquake based on high-resolution aftershock locations, Adv. Geosci., 14, 85-92, https://doi.org/10.5194/adgeo-14-85-2008, 2008.
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