Abstract:
This contribution examines the possibility of directly determining the timing of paleoseismic events by luminescence dating of sediments in sand dikes. Sand dikes are water escape structures (liquefaction features) formed in soft sediments due to the passage of seismically generated Rayleigh waves. Blending earlier studies of a crack dilatation model for the creation of sand dikes (Levi et al., 2008) and the studies on sonication of crystal slurries (Eddingsaas and Suslick, 2006), we posit that kinematic viscosity during the injection of liquefied sediments leads to a local transient heating of the injected material. Theoretical analysis of the injection process developed in this study shows that the instantaneous viscous flow of a sediment-water mixture through cracks in the overlying sedimentary strata can generate local temperatures of 350 °C or even more. Such temperatures can reset the luminescence signal of quartz grains in the liquefied sediments. Thereafter, the luminescence signal acquired by the quartz grains from their ambient natural radiation environment enables direct dating of these sediments; i.e. the timing of the causal earthquake. Given that the injection velocity (and hence the temperature rise) is highest at the centre of a dike, the sampling was from the core region of dikes.
Changes in the thermoluminescence sensitivity of the 110 °C glow peak of quartz (Sunta and David, 1982) were used to confirm that the viscous heating during sand dike formation did result in temperatures ≥ 350 °C. Stratigraphic consistency of luminescence ages of the dikes, the source sediments and their concordance with the published radiocarbon ages confirms the applicability of luminescence for their dating and provide evidence of three large earthquakes ∼0.30 ± 0.03, 1.0 ± 0.10 and ≥ 1.5 ka ago.