It is not surprising that Indonesia is one of the world's most earthquake-prone countries.
It straddles both of the planet's most active seismic belts, which between them account for 98 per cent of the greatest shocks.
The more celebrated of them is the "Ring of Fire" - or circum-Pacific belt
- which runs right around the Pacific Rim from New Zealand, through Japan and San Francisco to Chile.
It is responsible for 90 per cent of the world's earthquakes, including four-fifths of the most severe shocks.
Along Indonesia's north-eastern islands, the largest of which are New Guinea and Borneo, the shocks are caused by clashes between the Australian and Pacific tectonic plates.
Yesterday's quake, however - like the one that caused the tsunami on Boxing Day 2004 - happened along the lesser-known Alpide belt.
This extends from Java, which was shaken yesterday, through northern Sumatra, the epicentre of the 2004 disaster, throughthe Himalayas to the Mediterranean and outinto the Atlantic.
In the Indonesian area it is dominated by friction between the Australian and Eurasian plates.
While the Alpide belt produces fewer shocks, a greater proportion of them are severe.
It accounts for just 6 per cent of the world's earthquakes, but 17 per cent of the most serious ones.
A third severe Indonesian earthquake - measuring 8.7 on the Richter scale - shook the coast of Sumatra, along the Alpide belt, on 28 March 2005, killing 1,000 people.
In December 1992 another quake killed at least 2,200 on a string of islands in the country's East Nusa Tenggara province, which includes Flores and West Timor.
Mount Merapi, a volcano near the site of yesterday's shock, also began erupting earlier this month, but experts say that it did not cause the earthquake.
- INDEPENDENT
