EARTHQUAKES - A SHORT NOTE
Why does the Earth quake?
The surface of the Earth is like a massive jigsaw puzzle made up of huge rocky pieces called tectonic plates. The pieces of this puzzle are constantly moving about very slowly, but with immense force. If they slide past or crash into each other the Earth shakes and quakes. According to the United States Geological Survey, there are more than 3 million earthquakes every year. That's about 8,000 a day, or one every 11 seconds! Most of these are too weak to be noticed. Most earthquakes occur at depths of less than 80 km below the Earth's surface.
Scientists measure earthquakes in two different ways - by its magnitude or its intensity. Magnitude means the power of the shock waves and it's usually measured on the Richter scale. The Modified Mercalli Intensity scale measures the effects of an earthquake.
What are the warning sign?
Some people claim that you can predict an earthquake by spotting changes in some animals' behavior in the days before an earthquake.
- Hens stop laying eggs.
- Bees leave their hives.
- Rats, weasels, and centipedes leave their homes in large numbers.
- Dogs bark or whine excessively.
- Flamingos abandon their low-lying breeding grounds.
- Mass migration of toads to safer ground.
Cracks in the Earth:
|THINGVELLIR RIFT, ICELAND|
In some places you can clearly see the cracks, called faults, at the edges of the Earth's plates.
- THINGVELLIR RIFT, ICELAND: These exposed fault lines show the rift that lies on the boundary separating the American and Eurasian plates.
- SAN ANDREAS FAULT, CALIFORNIA, USA: This is a strike-slip fault, which indicates that the rocks move sideways and in opposite directions.
- GREAT ALPINE FAULT, NEW ZEALAND: This fault line runs almost the entire length of New Zealand's South Island and is visible from space.
Most famous Earthquakes:
- 1755 LISBON, PORTUGAL:- One of the worst earthquakes in history was followed by a tsunami and many fires.
- 1906 SAN FRANCISCO, USA :- Fires following this massive quake left 3,000 dead and 20,000 homeless.
- 1964 ALASKA, USA :- This powerful quake lasted nearly five minutesand was followed by a tsunami.
- 1995 KOBE, JAPAN :- Lasting barely 20 seconds, this quake killed 6,400 people and caused US $ 200 billion in damage.
- 2003 BAM, IRAN :- The city's many mud-brick buildings were destroyed by this massive earthquake.
|2003 BAM, IRAN|
Most powerful earthquakes:
- CHILE, 22 A: MAY 1960; Richter measure - 9.5
- PRINCE WILLIAM SOUND, ALASKA : 28 MARCH 1964 ; Richter measure - 9.2
- INDIAN OCEAN : 26 DECEMBER 2004; : Richter measure - 9.1
- ANDREAN OF ISLANDS, ALEUTIAN ISLANDS : 9 MARCH 1957; : Richter measure - 9.1
- KAMCHTKA, RUSSIA : 4 NOVEMBER; : Richter measure - 9.O
- SENSBI PROVINCE, CHINA : 23 JANUARY 1556; People killed - 830,000
- TANGSHAN, CHINA : 28 JULY 1976; People killed - 242,000
- KANSU, CHINA : 16 DECEMBER 1920; People killed - 180,000
- TOYKO-YOKIHAMA, JAPAN: 1 SEPTEMBER 1923; People killed - 140,000
- GULF OF CHIHLI, CHINA : 27 SEPTEMBER 1290; People killed - 100,000
- CATANIA, SICILY, AND NAPLES, ITALY: 11 JANUARY 1693; People killed - 60,000(Catania) and 93,000 (Naples)
- SHEMAKHA, AZERBAIJAN : 25 NOVEMBER 1667; People killed - 80,000
- MESSIAN, ITALY : 28 DECEMBER 1908
- KANSU, CHINA : 26 DECEMBER 1932 ; People killed - 70,000