[HCG23-P07] Identification of earthquake-triggered surficial sediment remobilization and implications on turbidite paleoseismology
Keywords:Turbidite , Paleoseismology, surficial slope remobilization
Using multi-method analyses we here investigate slope sequences of the Japan Trench and Chilean lakes. We compare results from i) stratigraphic correlations, ii) geochemical proxies (short-lived radionuclides, pore water geochemistry, high-resolution geochemical analyses by XRF core scanner), and iii) sediment-physical proxies (CT-scans, shear strength) to pinpoint gaps in the stratigraphy linked to surficial erosion. The sediment of the Chilean lakes is nicely laminated making it ideal for stratigraphic correlation by image analyses and high-resolution geochemical profiles. Sediment of the Japan Trench is optically homogenous and often disturbed by bioturbation making geochemical analyses more suitable to study this area.
Preliminary results of both Japan Trench and Chile show promising results. Pb-210 concentrations from a slope core taken on the trench-ward lower slope of the northern Japan Trench show a surficial erosion related gap in the stratigraphy possibly linked to the AD1968 Mw 8.3 Tokachi earthquake. Also, stratigraphic correlation of Chilean slope and basin sequences show an unconformity of a few centimeters caused by earthquake-triggered surficial remobilization. An additional 32 cores were taken on the slope of two Chilean lakes to constrain the effect of slope gradient and orientation on surficial erosion processes. Both the Japan Trench and Chilean lakes support diatom-rich sediments intercalated with tephra layers, making their geotechnical characteristics comparable. Lakes serve as an ideal natural laboratory where data acquisition is cost-effective and boundary conditions are well known, whereas the ocean setting is much more complicated, though allows an insight into the large-scale implications of seismically-triggered sediment transfer to the deep ocean.
To facilitate production of turbidity currents by remobilization of surficial sediment virtually no recharge of sediment is needed between earthquakes, in contrast to the production of subaquatic landslides. This would mean that, through the process of surficial erosion, turbidite paleoseismic records from closed basins (i.e. not affected by large subaquatic landslides or canyon-derived turbidites) can be continuous and of high sensitivity. As the mechanism has been found at both lake and ocean margins, this remobilization process might be of worldwide significance.