PARIS, June 22: Earthquakes have occurred regularly throughout history, often taking a massive toll in human life.

In many regions of the world they are regarded as inevitable hazards that are almost impossible to predict.

Following is a fact-file about earthquakes:

The intensity of earthquakes is measured either on the open-ended Richter scale, the most widely used, or on the Mercalli scale, mostly used in Japan and the former Soviet republics.

The Richter scale, named after US seismologist Charles Richter who devised it in 1935, is logarithmic, meaning that each step up the scale represents a 10-fold increase in the amplitude of the waves of energy emitted by the earthquake. It can be interpreted as follows:

Magnitude 1 — earthquake detectable only by instruments

Magnitude 2 — barely detectable, even near the epicentre

Magnitude 3 — detectable near the epicentre, but causing minimal damage

Magnitude 4/5 — detectable within 20 miles (32 kilometres) of the epicentre; possible slight damage within a small area

Magnitude 6 — moderately destructive

Magnitude 7 — a major earthquake

Magnitude 8 — a great earthquake.

Earthquakes are monitored by the Worldwide Standard Seismological Network, which has more than 125 monitoring stations around the world that were originally set up to monitor nuclear weapons testing.

The energy released by the Hiroshima atomic bomb in August 1945 was the equivalent on 5.7 on the Richter scale.

An earthquake in Chile in 1960, originally measured at 8.3 on the Richter scale, was later upgraded to 9.5, making it the largest recorded earthquake in history.

The destructive effect of an earthquake depends not only on its size but also on the area’s population, the type of buildings and the natural events that can be triggered.

Timing is also an important factor. The century’s worst earthquake in terms of numbers of people killed occurred at 3.42 in the morning, levelling the city of Tangshan, in China, while most people were asleep, on July 27, 1976, and killing more than 240,000. Its intensity was measured at 8.2.

The most destructive earthquake in recorded history also occurred in China, on January 23, 1556, in Shansi province where an estimated 830,000 people died.

An earthquake near Calcutta, India, on October 11, 1737, is estimated to have killed around 300,000 people.

The earthquake at Lisbon on November 1, 1755, which killed around 70,000 people, had important literary repercussions since it played a significant role in inspiring the French philosopher Voltaire to write his satire “Candide”.

Following is a list of other killer quakes in recent years:

1988

Dec 7: In Soviet Armenia: 25,000 dead in a quake measured at between 6 and 7 points on the Richter scale.

1990

June 21: In northwestern Iran: 40,000 killed in Ghilan and Zandjan provinces (magnitude 7.7).

July 16: on Luzon, the main island in the Philippines: more than 2,600 dead and missing, with 3,440 injured (7.7).

1991

Feb 1: in Afghanistan and Pakistan: at least 1,500 dead (6.8).

Oct 20: in northern India, at the foot of the Himalayas: 768 dead (6.1).

1992

March 13: in eastern Turkey: 653 dead and missing, around 700 injured (6.8).

Oct 12: near Cairo, Egypt: 552 dead (5.5).

Dec 12: on Flores island, in Indonesia: more than 2,000 dead (6.8).

1993

Sept 30: in Maharashtra state, western India: around 7,600 dead (6.4).

1994

June 6: in southern Colombia: more than 600 dead and 500 missing (6.0).

August 18: near Mascara, in western Algeria: 171 dead, 289 injured (5.4).

1995

Jan 17: in the Kobe-Osaka region of central Japan: almost 6,500 dead (7.2).

May 27, on Sakhalin island in the Russian far east: 1,841 dead.—AFP