Luminescence studies on the sediments laid down by the December 2004 tsunami event: prospects for the dating of palaeo tsunams events and for the estimation of sediment fluxes

Abstract

The tsunami of 26 December 2004 was associated with an Mw 9.3 earthquake. This was the second largest earthquake ever recorded. Geodynamic processes leading to such earthquakes suggest that these are repetitive. It is therefore desirable to obtain their recurrence interval. Earlier attempts to date palaeo-tsunami sediments have assumed that the basic premises for the use of optically stimulated luminescence (OSL) are adequately met. The sediments transported by the 2004 tsunami provided a maiden opportunity to verify the basic premises of the zeroing of the luminescence at the time of deposition. Results on eight of the nine samples using the conventional single aliquot regeneration (SAR) method provided OSL palaeodoses in the range 0.5 to 0.7 Gy. The recently developed component-specific SAR (CS-SAR) consistently provided OSL palaeodoses in the range 0.5-0.7 Gy. Further, CS-SAR consistently provided evidence that in eight of the nine samples, a fraction of the sample did experience daylight bleaching during transport with the tsunami. This was suggested by the fast-component OSL palaeodose of ~0.2 Gy. This implies a maximum age offset of ≤ 50 yrs and suggests that despite its energy and wave amplitude, only the top ~20-50 cm layer of the sediment in the intertidal zone was mobilized. This inference can be used for sediment influx calculations and hence for regional disaster management.