A missing-link in the tectonic configuration of the AlmacA +/- k Block along the North Anatolian Fault Zone (NW Turkey): Active faulting in the Bolu plain based on seismic reflection studies

Abstract

The North Anatolian Fault Zone (NAFZ) starts to branch off in the western Bolu plain. The branches of the NAFZ in this location create the AlmacA +/- k block which is surrounded by the latest surface ruptures of significant earthquakes that occurred between 1944 and 1999, but its northeastern part remains unruptured. The most recently formed rupture, that was a result of the 1999 November 12 Duzce earthquake, ended to the northwest of the Bakacak Fault. The connection between the Bakacak Fault and the main branch of the NAFZ via the Bolu plain has until now remained unknown. This paper establishes that the route of the missing link runs through the Dagkent, Kasaplar and Burnuk faults, a finding achieved with the help of seismic reflection studies. The paper also argues that the cross cutting nature of these newly determined faults and a stress analysis based on focal mechanism solutions of recent earthquakes demonstrate the termination of the suggested pull-apart nature of the Bolu plain.