Spatial and Temporal Variability of Slip Rates on the Tuz Gölü Fault Zone: Insights from Zircon Double Dating of Offset Lavas of Mount Hasan, Central Anatolia 

Abstract

Accurate knowledge of fault displacement rates is essential for seismic hazard assessments, with long-term slip rates being critical as constraints for the tectonic drivers of seismicity. The Tuz Gölü Fault Zone (TGFZ) is a NW-SE trending ~200 km long structure within the central Anatolian continental plateau. It consists of eleven parallel or sub-parallel fault segments, each ranging in length from 9 to 30 km, but seismic activity is scarce, making it difficult to pinpoint deformation mechanisms and magnitudes. Previous studies suggested that the TGFZ can produce earthquakes between M = 6.1 and 6.8, with generally higher displacement rates in the southern part of the TGFZ compared to the northern segments. Here, we studied the Akhisar-Kilic segment, which is located in the southern part of TGFZ. It dissects the southeastern flank of Mount Hasan, a prominent active stratovolcano, where several upper Pleistocene lava flows exhibit morphological evidence for faulting and hydrothermal activity. We conducted zircon double-dating, which merges U-Th and U-Pb geochronology and (U-Th)/He thermochronology, to date these variably offset lavas in order to establish fault geometries and offset rates.Zircon crystallization ages of four lava flows, sampled in duplicate or triplicate on both sides of the TGFZ, permit correlation between proximal parts of the flows, and the more distal lobes across the TGFZ. The youngest zircon crystallization age population in each of the two northernmost flows overlaps within error, and they are closer to equilibrium than for the middle and southern flows. (U-Th)/He dates record eruptive cooling and indicate a systematic increase from north to south, with eruption ages between 39.0 ± 1.0 and 151 ± 3 ka.Detailed morphological study of faulted lava flows utilizing a 5-meter digital elevation model (DEM) demonstrates that reasonable lava flow geometry can be restored within a range of oblique slip scenarios, ranging from primarily dip slip offset, to moderate right lateral oblique offsets. Combining the age dating and the geomorphic analysis yields vertical slip rates that can range up to between 0.5 and 0.6 mm/yr over the duration of lava emplacement in the southeastern sector of Mount Hasan. Because these rates are faster than previous estimates, we also expect that some TGFZ segments have the potential to produce earthquakes with considerably higher magnitudes than previously claimed. New slip rates covering a significant portion of the Late Pleistocene extend the fault history beyond the timescales of geodetic monitoring and historical records, thereby offering a significant vantage point for the derivation of seismic hazard estimates based on fault analysis. This is crucial to advance assessment of the multiple volcano-tectonic hazards that result from the coexistence of an active volcano and an active fault zone.Keywords: multiple volcano-tectonic hazards, offset lavas, slip rates, zircon double dating