Abstract

Based on historical and instrumental data, societies in the Eastern Mediterranean and Middle East have survived at least 150 large earthquakes (generally M > 6) during the past 2500 yr. Beyond this time span, an earthquake chronology is mostly unknown, which hampers the production of reliable long-term earthquake models. Since the only remaining evidence of seismic activity is a bedrock scarp, cosmogenic 36Cl is the only suitable nuclide to be applied in the determination of the seismic history and slip rate of an active limestone fault plane. In this study, we focus on the 4-m-high Mugırtepe fault scarp within the active Manisa fault zone in western Anatolia, one of the most seismically active and rapidly extending regions in the world. We analyzed 44 samples in two slightly overlapping strips, which in total covered 2.65 m of the fault scarp. In order to determine the timing and the amount of slip of the paleoseismic events, we analyzed the measured 36Cl concentrations using the Schlagenhauf Matlab® code. We used two different scenarios based on two different inherited 36Cl concentrations as constrained by our data and modeling. The best fit for the first scenario yields two seismic events, one at 13.7 ± 0.8 ka with a displacement of 0.5 ± 0.2 m and one at 7.8 ± 0.5 ka with 2.15 ± 0.35 m offset. For the second scenario, we obtained a single seismic event at 8.6 ± 0.6 ka with 2.65 ± 0.35 m of slip. These results indicate that the visible part of the Mugırtepe exposed fault scarp had achieved most of its displacement already by 8 ka. Initial surface faulting at Mugırtepe occurred not later than around 14 ka, and marked seismic activity continued until around 8 ka. Our first results from the western Anatolian Extensional Province show the ability to reveal periods of enhanced seismic activity beyond historical data using cosmogenic 36Cl.

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