Indonesia quake triggered by Dec. 26 mega-shock

Indonesia quake triggered by Dec. 26 mega-shock

Michael Perry
Reuters/Sydney

A huge undersea earthquake that killed hundreds in Indonesia
overnight was a result of increased geological stress caused by
last December's mega-quake that sent a devastating tsunami across
southern Asia, seismologists said.

And they warned of a third big earthquake in the area sooner
or later.

Monday night's 8.7 magnitude shock was centered 160 km
southeast of the epicenter of the 9.0 magnitude Dec. 26 quake off
Sumatra's northern tip. Geoscience Australia said the earlier
quake was two to four times larger.

Like the 2004 tremor, the latest one was a vertical earthquake
where part of the ocean floor was thrust upwards by another
tectonic plate pushing beneath it.

"It appears to be the same plate boundary where the Australian
plate is slipping beneath the Sumatran (Sunda) plate," Geoscience
Australia seismologist Phil Cummins told Reuters.

Seismologists had been warning of a second earthquake off
Sumatra due to the increased geological stress caused by last
December's quake.

Indonesia's disaster center said around 1,000 people had been
killed on the island of Nias, off Sumatra's west coast, which
took the full fury of the latest quake, one of the eight biggest
in the world since 1900. The country's vice president said on
Monday morning that the toll could reach 2,000.

Cummins said a third earthquake was to be expected because
geological stress levels would rise further following the latest
tremor.

"There is a chance that the next segment further to the
southeast could rupture sooner than we expected," he said.

"But we can't predict the time. Rather than 100 years it might
be 20 or 50 years," he said, but added it was possible it could
be in the next three months.

Last December's quake generated a tsunami that hit 13 Indian
Ocean nations, leaving more than 288,000 dead or missing.

The U.S. Geological Survey reported that Monday's quake was
located 2.065 degrees north and 97.010 degrees east. The Dec. 26
quake was located 3.307 degrees north and 95.947 east.

Both quakes were shallow, at a depth of 30 km, which
heightened the chances of a tsunami.

Australia's remote Cocos Islands in the Indian Ocean recorded
a tiny tsunami on Tuesday, with a 10-cm wave followed by a 25 cm
wave. Cocos recorded a 33-cm wave after the Dec. 26 quake.

Hawaii's Pacific Tsunami Warning Center, which issued and then
canceled a tsunami warning after Monday's quake, said early
warning systems put in place since December had worked.

"The international effort paid off. It all went smoothly,"
said the center's Dave Burwell.

Burwell said the center contacted a network of meteorological
and geoscience offices in Asia who then alerted local communities
to the tsunami warning.

The U.S. Geological Survey report on the latest earthquake
also said it was "likely triggered by stress changes caused by
the December 2004 earthquake".

Before that disaster, the previous quake of above magnitude 8
in this area occurred in 1861.