Complex dynamics of repeating and river-blocking landslides in Jiangda during 2018

Two large landslides successively blocked the Jinsha River at the same location in Jiangda Village on October 10 and November 3,2018,respectively.The dynamic processes and possible interactions of the two landslides need to be studied to better understand the physical processes involved,and to provide information on future disaster mitigation.We investigated their force histories and sliding directions by inverting regional broadband seismograms.The scale of the October landslide was approximately three times that of the November event.The October event revealed a particularly strong deceleration force,which may have been caused by a collision between the sliding mass and ground surface.In contrast,the November event had a relatively weaker deceleration force,indicating that it may have been gradually stopped by the landslide dam formed during the October landslide.The sliding directions of the two landslides differed significantly in terms of both horizontal and vertical directions,indicating a change in their sliding surfaces.We conclude that unconsolidated materials at the top of the October landslide continued sliding along a curved slope during the November event.From our seismic models of dynamic processes,both the October landslide and local background may have affected and even changed a subsequent landslide’s mechanism.