Critical Displacement of Earthquake-Triggered Catastrophic Landslides

The critical displacement is referred to as a threshold for slope failure, compared with the calculated permanent displacement under seismic load using Newmark displacement analysis. The critical displacement, usually obtained from laboratory shear tests under low and constant shear rates, is defined as the coseismic displacement beyond which strength of sliding surface reach residual values. The typical value ranges a few centimeters, depending on the frictional characteristics of sheared materials. However, this definition of the critical displacement might be oversimplified since the strength of sliding surface is velocity-dependent. Therefore, we collected the shear tests results of different materials under different shear velocities to evaluate the velocity-displacement dependency. Besides, we redefine the critical displacement of catastrophic landslide (D-cr) as the accumulated permanent displacement before rapid slide occurred. The influence of the strength and seismic parameters on the newly defined critical displacement is assessed using Newmark displacement analysis incorporating velocity-displacement dependent friction law. The dip angle of sliding surface is assumed as 15 degrees. The synthetic seismic load is simplified as sinusoidal wave with peak ground acceleration of 600 gal. Different seismic frequencies of 0.5, 1.2, 2.0 Hz are used to evaluate the influence of frequency on D-cr. The results show that the range of D-cr is much higher than few centimeters, and D-cr is highly related to frictional characteristics of sheared materials, especially within the slip-weakening distance. Moreover, D-cr is also influenced by frequency rather than peak ground motion acceleration of the sinusoidal wave. This study highlights that the initiation of landslide are extremely complex, which can be function of frictional law, seismic frequency, and geometry of sliding plane. The reasonableness of the velocity-displacement dependent friction law and the representative of the seismic wave should be considered for evaluating the initiation of catastrophic, rapid moving landslide.