The earthquake and tsunami in Indonesia caused widespread destruction and killed more than 1,400 people. Most deaths occurred in Palu.
Satellite data shows over 3,000 buildings were destroyed in the Palu city area along with bridges and roads Photographs illustrate the destructive power of the wave.
Palu Bridge IV bore the full force of the tsunami as it hit the centre of the shoreline. Its metal frame, now a twisted wreck, lies in the mouth of Palu’s river.
As the coastline of the bay curves up to the East, more destruction is evident. Whole streets, residential blocks and roads are no longer there. An entire section of coastline featuring a concrete promenade and a park have been wiped away, with only water in its place. Data from BMKG, Indonesia’s meteorological, climatological, and geophysical agency, indicates the potential inundation as a result of the tsunami. The map below shows how far water could travel inland depending on wave height. Reports indicate waves reached as high as six metres.
Another cause of death and damage was a phenomenon called liquefaction. This occurs when soil and silt, saturated by water and shaken by the earthquake, acts like liquid, according to the United States Geological Survey website.
In the Palu neighbourhood of Balaroa, about 1,700 houses were swallowed up when the ground they were built on turned into liquid mud, the national rescue agency said.
Satellite images of the Petobo district, south of Palu’s airport, showed another large area of buildings seemingly wiped away.
“When the quake hit, the layers below the surface of the earth became muddy and loose,” said Sutopo Purwo Nugroho, spokesman of Indonesia’s national disaster mitigation agency.
“Mud with such large mass volume drowned and dragged the housing complex in Petobo so that most of them became as if they were absorbed. We estimate 744 units of houses are there.
Palu sits astride the Palu-Koro fault line, which runs north-south along the edge of Palu Bay. Geologists estimate segments of the fault have a slip movement among the highest in Indonesia, at 4 cm (1.6 inches) a year, exposing the area to a higher risk of quakes. In a strike slip earthquake, two sides of a fault line scrape against each other horizontally.
Dr Austin Elliott of the Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET), at the University of Oxford, notes that a large shift along the fault caused the strong shaking.
“Tracking surface features in satellite imagery, we see up to 7 metres of displacement in opposite directions across the sharp fault surface break, which runs straight through Palu City and offshore. Importantly, this detailed satellite imaging reveals that the fault ruptured 60-70 km further south than early seismic data indicated, meaning a much larger area and population was impacted by violent shaking than originally estimated.”
The map below is derived from tracking correlative pixels between two satellite images of the same area, and calculating the distance they moved from one image to the next. A clear rupture can be seen stretching south from Palu city between two sections of land moving in opposite directions.