A continuous 18-10.2 ka paleo-earthquake events revealed by the Luobozhai lacustrine sediments, eastern Tibetan Plateau

Abstract

To assess the regional seismicity during the late Quaternary, we studied a well−exposed sequence of Luobozhai lacustrine sediments, 14.5 m thick, near Lake Diexi in the upper reaches of the Minjiang River, eastern Tibetan Plateau. High-resolution geochemical, grain-size, and magnetic susceptibility indicators were then used to obtain a continuous record of the changes in elemental and physical properties within the profile to determine additional seismic events that did not result in soft sediment deformation structures. Rapidly deposited layers with underlying soft sediment deformation structures in the Luobozhai section indicate 18 siliciclastic-enriched sandy sediment fluxes from earthquake-triggered landslides or dust of siliciclastic-enriched clastic materials; isolated rapidly deposited layers (without underlying soft sediment deformation structures) record 17 additional earthquake-induced inputs of detrital material into the lake. Hence, there are a total of 35 seismic events (M ≥ 5.0) recorded within the Luobozhai section, which probably reflects the frequent seismicity of Minjiang fault. Optically stimulated luminescence and 14C dating of the Luobozhai section indicates continuous sediment deposition from 18 to 10.2 ka, and had a mean recurrence interval of approximately 224 years. Heavy mineral analysis shows that event layers and non-event layers have different mineral compositions. This reflects changes in sedimentation pre, during, and post a seismic event, especially the co-seismic debris material (e.g., from landslides and/or dust storms) that controls changes in provenance within the drainage basin, and in turn affects the regional erosion rate and weathering patterns. This study opens up new avenues of paleo-earthquake research.