Kento Nakao, Hajime Naruse 

This study proposes a new method of inverse analysis of ancient turbidites to represent non-steady turbidity currents and account for multiple grain-size classes. The forward model employed in this study is based on the shallow water equation, and the initial conditions of flows are assumed as a lock-exchange type. To obtain a solution to the inverse problem, a genetic algorithm is employed to determine the optimal initial conditions. The present method successfully estimated the true initial conditions of the turbidity currents from the artificial data sets of deposits created by the forward model. The method is also applied to a turbidite bed of the Kiyosumi Formation. The results of the inverse analysis yield solutions that fits well with the observed data of the individual turbidite, and provide estimates of the flow velocity, flow thickness and sediment concentration of the turbidity current. The flow thickness and velocity when the turbidity current reached the downstream end of the study area were reconstructed to be 334.6 m, 0.98 m/s, respectively.