Finite Element Simulations of a Slump during the 2017 ML5.4 Pohang, South Korea, Earthquake

Abstract

During the 2017 local magnitude (ML) 5.4 Pohang, South Korea, Earthquake, a slump occurred on a natural slope with a fill which is located 3 km East from the earthquake epicenter. Notably, conjugated reverse faults cutting the Quaternary sediments near the ground surface were found in the vicinity of the slope toe through a trench survey. In addition, a maximum uplift of ground surface at the slope toe was measured about 1.0 m through the LiDAR image processing technique. This paper investigates the influences of the fill soil on top of the natural slope and the ground shaking on triggering the slump through finite element simulations. Three slope models are considered. Model A is a slope with a fill soil and a fault near the toe. Model B is a slope with the fill and without the fault, and Model C is a slope with the fault and without the fill. Acceleration time series available from the seismograph 8.17 km North of the epicenter are applied to the bottom of the three slope models as input motions. The numerical simulations for Models A and B predicted upward vertical displacements at the slope toe, showing good agreement with the uplift observed from the field. The vertical displacements for Models A and B were similar, implying the existence of the fault did not affect the triggering of slump. Model C does not produce any considerable amount of displacements, which implies a significant role of the fill soil in triggering the slump.