Indonesia tsunami clue found on seabed

Jakarta, Dec 11 (IANS) A scientific survey has found a clue to the tsunami that struck Indonesia in September that killed over 2,000 people, on the seabed, the media reported on Tuesday.

Damaging waves rushed ashore after the September 28 magnitude 7.8 quake, but researchers said at the time that they were surprised by their size, the BBC reported.

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.

Preliminary results of various investigations were being reported 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.

Two main surges of water were observed, the second being the biggest and pushing up to 400 metres 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 seabed in much of the bay dropped down in the quake.