12 Apr 2012

Tsunami alert cancelled after massive earthquakes

2:57 am on 12 April 2012

A tsunami alert was cancelled for most of the Indian Ocean region after two huge earthquakes in two hours under the sea off Indonesia's Aceh province.

Wednesday's quakes are not as big as the 26 December quake and tsunami that killed 230,000 people bordering the Indian Ocean in 2004, but Indonesian authorities say they were felt very strongly.

Scientists said on Wednesday evening there was little likelihood of a major tsunami.

The US Pacific Tsunami Warning Centre said the largest wave detected was less than a metre high so it's cancelled its tsunami watch.

The US Geological Survey says the first quake, measuring 8.6, struck at 2.38pm local time, 434km southwest of the city of Banda Aceh on the northern tip of Sumatra island at a depth of 33km, and was felt as far away as India and Thailand.

An 8.2-magnitude aftershock rattled the same area at 4.43pm, 615km south-south-west of Banda Aceh at a depth of 16km. Other tremors have also been felt.

After the quakes, phone and power links were out and people tried to reach higher ground, causing traffic jams.

Southeast and South Asian nations issued tsunami alerts and urged people to move to safety away from Indian Ocean coastlines. Most of those were cancelled by Wednesday night.

African countries including Kenya and Tanzania also issued warnings.

No tsunami watch was given for New Zealand or Pacific Island nations. New Zealand's Civil Defence says it will continue to monitor the situation.

Horizontal quake

Indonesia straddles the Pacific Ring of Fire, a zone of major seismic activity.

Bruce Pressgrave from the US Geological Survey told the BBC the nature of Wednesday's quake - a "strike-slip" fault - makes it less likely for a tsunami to be generated as the earth had moved horizontally, rather than vertically, therefore had not displaced large volumes of water.

Larger tsunamis are usually created by quakes with vertical movement, or by landslides into the sea.

The Aceh province was devastated after a 9.1-magnitude quake triggered a huge tsunami on 26 December 2004 that left 170,000 dead or missing, and that in total killed about 230,000 people in 13 Indian Ocean nations.