Systematic imaging of bimaterial interfaces at the at the Karadere-Düzce segment of the North Anatolian Fault Zone, Turkey

Abstract:

We investigate the presence and properties of bimaterial interfaces at the Karadere-Düzce segment of the North Anatolian Fault Zone (NAFZ) in NW Turkey with observations of fault zone head waves and direct P body phases. The tectonic loading on the NAFZ produces major (M7+) strike-slip earthquakes. The two most recent major earthquakes in the study region were the 1999 Mw 7.4 Izmit and Mw 7.1 Dücze events. In the present study we use waveform recordings from near-fault stations along the broader Karadere-Düzce area operating during the Izmit and Duzce aftershock periods. We analyze the data using automatic detection of direct P and fault zone head waves along with the manual inspections and particle motion analysis. Preliminary results indicate abundant early arrivals before the direct P at many stations that appear to be head waves, but show no moveout with different source-receiver distances. These phases may reflect local bimaterial interfaces near the stations that may be associated with fault-zone-related basin structures. We also observe at some stations head wave type signals before the direct P waves that show systematic move-out with increasing propagation distance along the fault and may indicate a deep velocity contrast across the NAFZ in the area. Updated results will be presented in the meeting.