- An earthquake is any motion of the ground, no matter
what the cause. They range from being imperceptible to
being so violent that they can raze cities. No part of the
world is exempt from earth quakes.
- Earthquakes happen as a result of the release of energy
when rocks come under pressure, mainly from plate
movements, shift or fracture.
- A few earthquakes are triggered by meteorite impacts,
man-made explosions, or the weight of water, for instance
behind a dam.
- Earthquakes produce three main types of seismic
waves: primary (P),secondary(S) and surface(L).
- Earthquakes prediction the best defense against their
effects, is still an inexact science
Where earthquakes happen
Most earthquakes occur at plate
boundaries; 70 per cent
occur around the pacific, including
the San Andreas fault
region. Earthquakes also occur within
continents, such as
Tangshan in 1976. This map shows the regions with
the
greatest concentration of earthquakes activity.
How earthquakes happens?
An earthquake, the result of a sudden release of energy in
the Earth’s crust, is measured with a seismometer. An
earthquake with magnitude 3 or lower is mostly
imperceptible while magnitude 7 can cause serious damage
over large areas. The shaking in earthquakes can also
trigger landslides and sometimes volcanic activity. In
contrast, earthquakes are caused by volcanic activity,
landslides, and nuclear tests.
Seismic waves which carry with them an enormous amount
of energy travel through the Earth’s crust. The earthquake
which seismic waves cause will vary in strength and
duration. This depends on the strength of the seismic
waves. Let’s discover how earthquakes happen.
Where plates diverge, lava emerges from the mantle and cools to form new sections of crust.
Point of friction
Primary waves (longitudinal or compressional waves) and S-waves (transverse or shear waves)
Surface waves radiable outwards from the epicenter which is the point directly above it on the surface of the Earth
Particle motion
Love waves, named after British mathematician A.E.H Love, is a surface wave having a horizontal motion that is transverse to the direction the wave is traveling.
The largest earthquake with 9.5 magnitude occurred on 22
Indian Ocean earthquake, one of the largest recorded May
1960. Its epicenter was near Canute, Chile. The 2004
earthquakes which have all been mega thrust earthquakes,
is one of the deadliest earthquakes in history. In January
2010, the worst 7.0 magnitude earthquake in two centuries
struck less than ten miles from the Caribbean city of Port-
Au-Prices, Haiti, causing damages to Haitian.
Earthquake record
Place Date Key fact
Shanshi 1556 highest know death toll - 830000 people died. china has
China the worst record for earthquakes deaths
Lisbon 1755 Worst in Europe - 8.7 on Richter scale. 70000 people died
Portugal and the entire city was destroyed. Tremors were felt in North
Africa, England and Luxembourg.
Yakatut bay 1899 Greatest recorded vertical movement - the coast rose in
Alaska places by 14.5m (47 ft).
San Franciso 1906 Destroyed most of the city, and a huge fire burned for 3
USA days. Survivors included the celebrities Enrico Caruso and
John Barrymore.
Off Chile 1960 Largest earthquakes ever recorded - registered 9.9 on the
Richter scale.
Alaska 1964 Longest recorded - 4minutes (Lisbon in 1755 was a 10-
minute series of shocks).
Tangshan 1976 Deadliest in the 20th century - 8.0 on the Richter scale.
China 655000 people died.
Kobe 1995 Worst damage financially - over US$ 147 billion of damage.
Japan 5500 people died.
Earthquakes gods
In the Bible, Yahweh speaks to the prophet Elijah as an
earthquakes. In African myth earthquakes are caused by the
dead of the underworld. The Greek god of earthquakes was
Poseidon , also god of sea. His roman counterpart was
Neptune. In Siberia the earthquakes god is Tuil, who rides
a sleigh beneath the earth.
