Revisiting the slip rate of Quaternary faults in the Iberian Chain, NE Spain. Geomorphic and seismic-hazard implications

Abstract

The seismogenic potential of active faults for seismic hazard analyses are typically constrained using slip rates. These parameters, derived from numerically dated Quaternary deposits and landforms, have a critical impact on seismic hazard estimates with relevant societal and economic implications. Recently published geomorphological and paleoseismic investigations on active normal faults in the intraplate Iberian Chain (Spain), based on OSL ages from a now closed commercial laboratory, indicate anomalously high slip rates and paleoearthquake frequencies and extremely high fluvial incision rates. Parameters derived from those numerical ages have been used for seismic hazard assessments at critical facilities. This work revisits the chronology of Quaternary deposits associated with several faults applying various geochronological methods: Electro Spin Resonance (ESR), AMS Radiocarbon, Optically Stimulated Luminescence (OSL) and U-series dating. The totality of the new numerical ages is markedly different from the previously published OSL ages. The thirteen new ESR, OSL and U-series ages are systematically between three and six times older than the previous OSL ages. These data strongly suggest that previous ages overestimate the activity of the faults and seismic hazard in the region. The lack of validity of the revisited OSL analyses is attributed to inadequate dating procedures. Slip rates calculated with the new numerical ages are consistent with the slip rates estimated using Pliocene markers in the Iberian Chain and the slip rates published for other normal faults in eastern Spain. The new geochronological data also indicate reasonable fluvial incision rates, comparable with those estimated in nearby regions. The findings presented in this work have also implications for other Quaternary geomorphological studies in Spain based on potentially non-valid OSL ages.