Surprise Palu Tsunami Clue Found on Seafloor

Jakarta, Scientists are getting closer to

understanding the tsunami that struck Palu in Indonesia in September.

Damaging waves rushed ashore after a Magnitude 7.8 quake, but

researchers said at the time that they were surprised by their size.

Now, a survey in the bay in front of the Sulawesi city shows

significant subsidence of the seabed. This likely contributed to the

abrupt displacement of water that then crashed on to land.

More than 2,000 people lost their lives in the disaster.

Preliminary results of various investigations are being reported here at

the Fall Meeting of the American Geophysical Union – the largest

annual gathering of Earth and space scientists.

The quake occurred on what is called a strike-slip fault, where the

ground on one side of a rupture moves horizontally past the ground on

the other side. It is not a configuration normally associated with very

large tsunamis.

Nevertheless, this is what happened in the early evening of 28

September, around prayer time. Two main surges of water were

observed, the second being the biggest and pushing up to 400m

inland.

Udrekh al-Hanif from the Indonesian Agency for Assessment and

Application of Technology (BPPT) in Jakarta, told the meeting that the

generation source of the tsunami had to be very close to the city

because of the short interval between the onset of the quake and the

arrival of the high water – less than three minutes.

He and colleagues have sought answers in a depth

(bathymetric) map of the long, narrow inlet that leads to Palu at its

head. The team is still working through the results, but the data

indicates the seafloor in much of the bay dropped down in the quake.

This, combined with a sharp movement of the crust northwards, could

certainly have produced a tsunami. When we overlap the bathymetric

data from before and after, we can see that almost all of the area of the

seafloor inside the bay subsides,” the Indonesian scientist said, the

BBC news reported.

Source: Oman News Agency