Earthquakes
The earth is never free from earthquakes for long and more than 50000 of them are
recorded annually. Minor earth tremors caused by gentle waves of vibration within the
earth’s crust occur every few minutes. Major earthquakes usually caused by movement
along faults, can be very disastrous particularly in densely populated areas. Earthquakes
themselves may cause only restricted damage in the regions of occurrence but their after-
effects can be very catastrophic. They produce gigantic tidal waves called tsunamis. In
severe earthquakes, fissures gap open, and the ground writhes and undulates in the passage
of the ‘surface waves’. Only the highly sensitive seismograph can record the movements of
earthquake waves.
Some Major Earthquakes
One of the major earthquakes ever known was the Great Lisbon Earthquake on November
1755.It originated in an abrupt subsidence of the ocean floor in the Atlantic west of Lisbon.
The earthquake on 1 September 1923 that shook Tokyo and Yokohama was equally
shocking. A fracture that occurs on the earth’s crust off the coast of Japan caused the
earthquake. Other disastrous earthquakes include that of San Francisco in 1906which ruined
the greater part of the heart of San Francisco. In the loess region of Kansu in China, the 1920
earthquake claimed 200,000 lives. In 1960,the earthquake at Agadir, Morocco sealed the
fate of 10,000 inhabitants.
The Distribution of Earthquakes
The world distribution of earthquakes coincides very closely with that of volcanoes. Regions
of greatest seismicity are circum-pacific areas, with the epicenters and the most frequent
occurrences along the ‘Pacific ring of Fire’. It is said that as many as 70 per cents of
earthquakes occur in the circum-pacific belt. Another 20 per cent of earthquakes take place
in the Mediterranean-Himalayan belt including Asia Minor, the Himalayas and parts of
North West China. Elsewhere the earth’s crust is relatively stable and is less prone to
earthquakes though nowhere can be said to be immune to earth tremors.
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The earth is never free from earthquakes for long and more than 50000 of them are
recorded annually. Minor earth tremors caused by gentle waves of vibration within the
earth’s crust occur every few minutes. Major earthquakes usually caused by movement
along faults, can be very disastrous particularly in densely populated areas. Earthquakes
themselves may cause only restricted damage in the regions of occurrence but their after-
effects can be very catastrophic. They produce gigantic tidal waves called tsunamis. In
severe earthquakes, fissures gap open, and the ground writhes and undulates in the passage
of the ‘surface waves’. Only the highly sensitive seismograph can record the movements of
earthquake waves.
Some Major Earthquakes
One of the major earthquakes ever known was the Great Lisbon Earthquake on November
1755.It originated in an abrupt subsidence of the ocean floor in the Atlantic west of Lisbon.
The earthquake on 1 September 1923 that shook Tokyo and Yokohama was equally
shocking. A fracture that occurs on the earth’s crust off the coast of Japan caused the
earthquake. Other disastrous earthquakes include that of San Francisco in 1906which ruined
the greater part of the heart of San Francisco. In the loess region of Kansu in China, the 1920
earthquake claimed 200,000 lives. In 1960,the earthquake at Agadir, Morocco sealed the
fate of 10,000 inhabitants.
The Distribution of Earthquakes
The world distribution of earthquakes coincides very closely with that of volcanoes. Regions
of greatest seismicity are circum-pacific areas, with the epicenters and the most frequent
occurrences along the ‘Pacific ring of Fire’. It is said that as many as 70 per cents of
earthquakes occur in the circum-pacific belt. Another 20 per cent of earthquakes take place
in the Mediterranean-Himalayan belt including Asia Minor, the Himalayas and parts of
North West China. Elsewhere the earth’s crust is relatively stable and is less prone to
earthquakes though nowhere can be said to be immune to earth tremors.
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