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Luminescence dating of P leistocene alluvial sediments affected by the A lhama de M urcia fault (eastern B etics, S pain) – a comparison between OSL , IRSL and post‐ IR IRSL ages

2011; Wiley; Volume: 41; Issue: 2 Linguagem: Inglês

10.1111/j.1502-3885.2011.00230.x

1502-3885

Reza Sohbati, Andrew Murray, Jan‐Pieter Buylaert, María Ortuño, Pedro P. Cunha, E. Masana,

earthquake and tectonic studies

The ages of nine alluvial units, identified by the integration of data obtained from five trenches at the southern termination of the A lhama de M urcia F ault ( AMF ) (eastern B etics, S pain), are constrained using luminescence dating based on the O ptically S timulated L uminescence ( OSL ) from quartz, I nfrared S timulated L uminescence ( IRSL ) at 50°C, and post‐ IR elevated temperature (225°C) IRSL signals from K ‐feldspar. All signals pass the routine tests associated with the Single Aliquot Regenerative ( SAR ) protocol, including the recycling ratio, recuperation, and dose recovery tests. The equivalent doses ( D e ), residual doses and anomalous fading rates (‘g’‐values) of the IRSL at 50°C ( IR 50 ) and post‐ IR IRSL at 225°C ( pIRIR 225 ) from K ‐feldspar are compared for 16 samples. The residual doses in laboratory‐bleached samples suggest that there is no significant unbleachable residual dose using these signals; the residual doses are 0.17±0.15 Gy and 0.93±0.80 Gy , respectively. For both signals, the residual doses appear to depend on the corresponding natural doses; that is, the larger the natural doses, the larger the residuals, an observation made for the first time for IRSL signals. The average fading rate for the pIRIR 225 (0.94±0.07%/decade, n = 48) is markedly lower than that for IR 50 (2.08±0.16%/decade, n = 48), indicating that the age correction for the pIRIR 225 is much smaller than that for IR 50 . The agreement between the quartz OSL , corrected IR 50 , and corrected pIRIR 225 for the two youngest samples suggests that the pIRIR 225 is an accurate dating signal in this age range (<25 ka). The oldest age obtained using the corrected pIRIR 225 signal is 320±20 ka for sample 098807; the corrected IR 50 age is only 154±15 ka. Although this suggests that the pIRIR 225 signal circumvents the effect of anomalous fading to a great extent, the resulting age cannot be regarded as necessarily accurate because of the limitations of the fading correction model used, and the absence of independent age control for the old samples. Nevertheless, our luminescence ages provide the first age constraints on the seismic activity of the southern termination of the AMF .