The International Information Center for Geotechnical Engineers

Tuesday, 23 October 2018 01:00

Massive landslides in Palu after Mw 7,5 earthquake in Sulawesi

Massive flow type landslides in Palu Massive flow type landslides in Palu.

Three major landslides have struck Palu city causing fatalities and significant structural damage after the Mw 7,5 earthquake in Sulawesi Island.

The devastating earthquake occurred on Friday, 28 of September 2018 triggering a tsunami that hit Palu city causing at least 2000 fatalities. The powerful shock provoked liquefaction incidents and according to Dave Petley, Pro-Vice-Chancellor (Research and Innovation) at the University of Sheffield in the United Kingdom, three shallow flow-type landslides. Many people were buried under the landslides or killed by collapsing buildings. Rescue teams inspected the area in search for survivors.

The village of Petobo (south of Palu) was highly damaged as hundreds of houses "were swallowed by the ground," as residents perceived the liquefaction phenomenon. Geological surveys show that area of Palu consists of marine and fluvial sediments that contain layers of quick-clay. Quick-clay causes landslides in a slightly different mechanism than soil liquefaction. In common liquefaction, pore pressure rise causes the loss of the soil's shear strength. However, in quick-clays, dynamic load triggers the collapse of the mineral grains' framework.

Satellite imagery data collected by DigitalGlobe show the enormity of the damage that the landslides caused. Building, roads and entire neighborhoods were wiped away in their path. Dave Petley stated:  "The landslide, which moved from east towards the west, appears to be a planar flowslide of some type, with a very strong lobate form away from the source. Note that the landslide debris itself is an extraordinary combination of soil and debris, and houses and buildings, all compressed together. The total loss of homes is very high, but it is hard to know as to the likely level of human casualties. There are multiple tension cracks in the headscarp area, and this will be a very challenging site in the next heavy rainfall event." Mr. Petley also commented on the smaller of the 3 main landslides that was relatively closest to the center of Palu: "Meanwhile, the smaller landslide at Balaroa, the site closest to the city center, is also terrible. On this occasion the landslide moved from west to east, and again a large, mostly evacuated, source area can be seen. There is a raft of mostly intact debris and vegetation downslope, and then an extraordinary compression zone of destroyed buildings. The slide is about 1 km long. The level of loss is once again high, but the number of fatalities is difficult to determine," he said.

 According to authorities, there will be no future constructions on the damaged area that will become a memorial for the victims.


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Giant landslide in Palu

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