Smaller impact on ocean floor

Indonesia's undersea earthquake on Monday had a much smaller impact than the December 26 quake that sent a killer tsunami across Asia, leaving 288,000 people dead or missing.

Seismologists said the reason the latest earthquake failed to create a large tsunami, despite being 8.7 magnitude compared with the December quake's 9.0, was that not as much of the ocean floor moved and most of its energy was directed away from Asia and into areas of the southwest Indian Ocean without major land masses.

"In terms of the size of the event, the main surface rupture of (this) earthquake was probably one quarter of that on Boxing Day - less ocean floor moved," said Geoscience Australia seismologist Trevor Allen.