Paleoseismological trenching and seismic hazard assessment of the Bozkurt Segment of the Maymundağı Fault, Acıgöl Graben, SW Türkiye

Abstract

The Ac & imath;g & ouml;l Graben in SW Turkey, ca. 50-55 km in length and 11-15 km in width, formed during the Miocene to Quaternary periods. This graben is bounded by active normal faults of Maymunda & gbreve;& imath; Fault (MF) to the northwest and the Gemi & scedil; Fault Zone (GFZ) to the southeast that have triggered significant earthquakes, causing considerable damage. This study focuses on the Bozkurt segment of the MF, which caused a damaging earthquake (Mw 6.0) in 2019 and another significant earthquake in 1886 during historical times. A paleoseismological trench survey along the Bozkurt segment revealed at least two faulting events, with the last event producing a vertical displacement of 0.25 m. The Optical Stimulated Luminescence (OSL) dating indicates that the last earthquake occurred 3.13 +/- 0.33 ka BP, while the penultimate earthquake occurred 4.0 +/- 0.72 ka BP. These dates correspond to a long-term slip rate of approximately 0.36 +/- 0.11 mm/a and a mean recurrence interval of 2.08 ka, short-term slip rate 0.78 +/- 0.16 mm/a and recurrence interval of 0.96 ka, and compatible with the mean sedimentation rate of 0.26 mm/a, calculated from drill logs in Acig & ouml;l basin-fill. Considering the 6 km length of the Bozkurt segment and its vertical displacement of 0.25 m in the last event, this segment has the potential to generate earthquakes ranging from 5.6 to 5.9 Mw. Long-term slip rates derived from geomorphological data are 0.56 mm/year to the north and 0.64 mm/a to the south of the graben, indicating higher subsidence on the southern margin. These rates are in accordance with the slip rates calculated from the paleoseismological trench survey and sedimentation rate from the drill-log. These indications show that the Bozkurt segment is an active Holocene fault with relatively long recurrence intervals and low-slip rate. Consequently, the paleoseismological studies in combination with geomorphological data are important tool to assess seismic hazards and to define the characteristics of individual fault segments.