Competency of Age-Depth Models in Decoding the Uplift-Subsidence Cycles and Earthquake Recurrence Patterns in Tectonically Active Coastal Zones

Chronologies impart crucial data of time-scales for events, and hence important in understanding rates for abrupt/terminal erosional and depositional processes. Sediments containing biogenic/organic assemblages serves as the basis for age-depth modelling as they provide a chronology of stratigraphic horizons. Age-Depth models are generated using Bayesian statistics to reconstruct accumulation histories for deposits, through combining radiocarbon (AMS) and optically-stimulated luminescence (OSL) dates. Information on sediment stratigraphy from 230 cm long composite logs are taken into account from a previous report on paleoseismic land-level changes in the study area, for which our age-depth models have justified a fine correlation. Site-1 core model shows three sections; a period of rapid and constant accumulation, then a significant stratigraphic event, and finally another period of progressive accumulation afterwards; both periods are divided by a break of extremely slow accumulation or a hiatus ranging from c. 180 to 190 cm depth (c. 2500-1300 cal BP). Site-2 core model shows four sections; a period of a slow accumulation from the deepest part of the core up to c. 160 cm depth alternated with comparatively faster accumulation up to c. 80 cm depth. Site-3 core model shows four sections; two periods of slower accumulation rate are bounded by the two periods of rapid accumulation. Site-3 core starts with a rapid phase of accumulation and continues up to c. 155 cm depth, succeeded by a tremendous decrease in the accumulation rate that continues up to c. 115 cm depth, afterwards a faster accumulation up to the surface. Age-Depth models of the three sites corroborate that the periods of rapid and gradual accumulations are indicative of coseismic and interseismic/postseismic subsidence respectively, whereas the chronostratigraphic hiatus and periodic gap of extremely slow or non-deposition are suggestive of coseismic and interseismic/postseismic uplift respectively. The present study establishes a modern proxy in decoding the history of land-level changes and earthquake recurrence patterns in tectonically active coastal regions and validates the competency of age-depth models in exploring the records of uplift/subsidence patterns associated with paleo-earthquakes.