Late Holocene coseismic rupture and aseismic creep on the Bolvadin Fault, Afyon Akşehir Graben, Western Anatolia

Authors: ÇAĞLAR ÖZKAYMAK, HASAN SÖZBİLİR, MERTKAN OSMAN GEÇİEVİ, İBRAHİM TİRYAKİOĞLU

Abstract: The Bolvadin Fault, which forms one of the northern boundaries of the Afyon Akşehir Graben, creeps aseismically on the surface of earth and has not generated surface-rupture earthquakes during instrumental time. Our geological mapping and palaeoseismological studies reveal that the Bolvadin Fault is an approximately 2 km wide and 16 km long, dip-slip normal fault. It could generate earthquakes up to Mw 6.48 roughly every 1 ka and the latest surface-rupture event (M > 6) occurred 494 ± 45 years ago on the Bolvadin Fault. The throw over the past 5 Ma is measured as approximately 500 m according to relative positions of the basal unconformity of Pliocene clastics on both sides of the fault yielding a long-term average slip rate of 0.1 mm/year. Palaeoseismic trenching at two sites on the Bolvadin Fault document that the fault was reactivated by at least two linear morphogenic earthquakes during the past 2570 years. They probably occurred in 530 (AD) and 1525 ± 45 (AD). We also determined a mean late Holocene slip rate of about 0.64 mm/year at trench 1. Palaeoseismic data suggests that aseismic surface deformations (postseismic relaxation) which began developing after the 2002 Çay earthquakes (Mw: 6.3 and 6.0) follows the older surface rupture of the Bolvadin Fault.

Keywords: Afyon-Akşehir Graben, Bolvadin Fault, palaeoseismology, slip rate

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