7.2 magnitude quake triggers Java tsunami

A massive earthquake shook the Indonesian island of Java on Monday, triggering a six-foot-high tsunami that killed nearly 100 people, Indonesia's Red Cross reports.

The 7.2 magnitude quake was followed by a 6.1 magnitude aftershock, which struck two hours later.

Each whole number difference in magnitude on the Richter scale equals a tenfold increase or decrease in an earthquake's amplitude.

In other words, the first quake released about 30 times more energy than the 6.1 magnitude aftershock that followed.

The wave from the tsunami was spawned 48 kilometres below the Indian Ocean and the resulting earthquake even caused some buildings as far off as Jakarta to sway for about two minutes.

It was also measured along Indonesia's island of Bali and parts of Australia's Coco Islands.

City officials failed to issue a warning system for Java before Monday's tsunami struck, even though an earthquake hit the city seven weeks ago and killed thousands.

This is the biggest tsunami to hit the islands since the 2004 Boxing Day disaster.

The 2004 tsunami was caused by an earthquake that measured 9.0 on the Richter scale.

Scientists have long referred to this area of the Pacific as the "Ring of Fire", prone to seismic activity which sometimes triggers tsunamis.

A tsunami sometimes happens when there is an "underwater earthquake".

This takes place when two tectonic plates rubs against each other along a fault line until one of the plates snaps, due to pressure from the other.

The end result is an earthquake, creating dramatic waves up to 34 feet in height.

Photography: The Guardian

Source: Discovery Channel Reports, July 17 edition