FMIPA UI Geologist, Reza Syahputra said that two possibilities caused an earthquake that led to a magnitude of 7.4 tsunamis in Palu, Central Sulawesi on Friday (28/9).
Previously, he revealed that the earthquake on the Palu was caused by the earth plates moving and pushing each other apart, there was a major fault that was quite large namely the Palu Koro fault that cut the “neck” region of Central Sulawesi.
However, Reza said several earthquakes that occurred did not originate from the main fault, but small faults around the Palu Koro fault.
“The earthquake point is not right in the Palu Koro fault but in the vicinity, there is a shift or movement in the fault area that is smaller than the Palu Koro, which is likely to cause an earthquake,” Reza said.
However, related to the tsunami with a height of up to 1.5 meters hit Palu and Donggala, Reza explained that there are two possible causes.
First, due to the existence of liquefaction or landslides of sand or soil material on the seabed of the Palu Koro bay that has not been well compacted. This was triggered by the movement of faults around Palu Koro. This, continued Reza, was thought to be a major factor in the tsunami.
“This earthquake did not directly trigger a tsunami. However, the strong earthquake vibrations due to the shifting of the faults were thought to be a factor for the tsunami, “he said.
The second possibility is purely due to a fault, the fault triggers the movement or rise of the fault elsewhere. However, Reza continued, the fault scheme in Central Sulawesi was not a fault scheme that could have caused a tsunami, Because usually, tsunamis occur as a result of an upward movement or downward fault. That is the movement of rocks vertically. So, because of the vertical movement, the seawater is shaken and causes waves to reach the land.
While the earthquake that occurred in Central Sulawesi was an earthquake caused by horizontal fault movement. Rock movement that occurs horizontally.
But indeed, continued Reza, from research in the last few years it was known that there was an incident that caused the landmass in Central Sulawesi to be raised several centimeters each year, and the rate of land removal was greater than in other places.
So that when there is a fault shift in one area, it will trigger an uplift in another area.
“It is the possibility that the fault was only moving horizontally, but there is an element of vertical movement as well,” he added.
The Palu quake was centered on the mainland, but the formation of the Palu bay has made the tsunami energy undergo amplification with greater energy.
