EARTHQUAKES

What causes Earthquakes? Plate Tectonics Where do Earthquakes occur? Measuring Earthquakes Prediction and Warning Major Earthquakes Earthquake in Chile Biblical Accounts Personal Account

The aftermath of an earthquake (World Disaters - Earthquakes)

What causes Earthquakes?

Earthquakes are caused when tension is released from the rocks in the Earth's crust and upper mantle. This tension is due to friction between what scientists believe are large 'plates' floating on magma on the Earth's surface. Sometimes earthquakes happen when the rocks in the earth's crust bend and break. This causes shock waves to travel on the earth's surface, resulting in widespread destruction.

Plate Tectonics

Scientists believe that the earth is made up of four main layers. The outermost layer being the crust, then the mantle, the outer core and at the centre of the earth the inner core. The crust is made up of hard rock, mainly granite. The mantle is mainly molten lava on which the crust is floating. The core is mostly iron, with the outer core being liquid and the inner being solid. The mantle is continually moving; this is called convection. It is also believed that the earth is divided into more than a dozen plates, which are floating on the mantle. This theory is called plate tectonics . The plates often rub together, pull apart, collide or dive under one another. These movements cause earthquakes and also volcanoes.

Where do Earthquakes occur?

Earthquakes usually occur in places where two plates meet, called faults. Earthquakes are mostly generated deep within the earth's crust, when the pressure between two plates is too great for them to be held in place. The underground rocks then snap, sending shock waves out in all directions. These are called seismic waves. The underground origin of an earthquake is called the focus. The point at which an earthquake originates on the surface is called the epicentre.

Measuring Earthquakes

The Mercalli Scale

The original scale for measuring the severity of earthquakes was compiled by the Italian Seismologist, Guiseppe Mercalli, in1902. It has gone through a number of revisions since then. The Mercalli Scale relies on how much damage is caused by an earthquake.
Currently it runs as follows:

I	Only felt by instruments.	VII	Most people run outdoors. Damage to weakly constructed buildings. Felt by people in moving vehicles.
II	Felt by people at rest, especially on upper floors. Suspended objects may swing.	VIII	Considerable damage to most buildings. Heavy furniture overturned. Some sand fluidised.
III	Felt indoors. Vibrations like passing traffic.	IX	Even well-designed and sturdy buildings badly damaged, moved from their foundations. Ground cracks. Pipes break.
IV	Many people feel it indoors, a few outdoors. Crockery and windows rattle. Standing cars rock. Some sleepers awake.	X	Most masonry destroyed. Landslides occur. Water slops from reservoirs and lakes. Railway lines bend.
V	Felt by nearly everyone. Tall objects rock. Plaster cracks.	XI	Few structures remain upright. Bridges fall. Extensive fissures in the ground. Underground pipes totally out of action.
VI	Most people run outdoors. Damage to weakly constructed buildings. Felt by people in moving vehicles.	XII	Total destruction. Ground thrown into waves. Objects flung into the air. You would be lucky to survive this one.

The Richter Scale

The Richter scale is a scale designed by A. Richter to measure the strength or intensity of the shock waves produced by an earthquake. The scale is measured in steps from one upward. Each successive unit is ten times more powerful than the one before. Therefore an earthquake that measures 7.0 on the Richter scale is 1000 times more powerful than an earthquake measuring 4.0. Little damage is done by an earthquake below 4.0; an earthquake of 7.0, however, would cause widespread disaster.

An artists impression of the Richter scale.

Scale about 3.0	Scale about 6.0	Scale about 9.0

Major Earthquakes

Date Location Death toll Magnitude 1290 Gulf of Chihli, China 100 000 unknown 1556 Shensi, China 83 000 8.3 (est.) 1667 Shamkha, Caucasia 80 000 unknown 1692 Port Royal, Jamaica 2 000 unknown 1755 Lisbon, Portugal 60 000 8.6 (est.) 1797 Quito, Ecuador 40 000 unknown 1835 Concepcion, Chile 5 000 8.5 (est.) 1835 Northern Japan 28 300 7.6 (est.) 1905 Jammu and Kashmir, India 19 000 8.6 (est.) 1906 San Francisco, USA 700 8.3 (est.) 1908 Messina, Italy 83 000 7.5 (est.) 1915 Avenazzo, Italy 29 980 7.5 (est.) 1920 Gansu, China 100 000 8.6 (est.) 1923 Tokyo, Japan 99 330 8.3 (est.) 1927 Nan-Shan, China 20 000 8.3 (est.) 1932 Gansu, China 70 000 7.5 (est.) 1935 Quetta, India 30 000 7.5 (est.) 1939 Erzincan, Turkey 30 000 7.9

Date Location Death toll Magnitude 1939 Chillan, Chile 28 000 8.3 1948 Turkemenistan 110 000 7.3 1960 Agadir, Morocco 12 000 5.7 1960 Chile 5 000 8.3 1963 Skopje, former Yugoslavia 1 000 6.0 1964 Anchorage, Alaska 131 8.4 1970 Northern Peru 66 794 7.7 1970 Yunnan, China 10 000 7.7 1976 Guatemala City, Guatemala 23 000 7.5 1976 Tangshan, China 242 000 8.2 1977 Bucharest, Romania 1 600 7.2 1978 Tabas, Iran 25 000 7.7 1980 Al Asnam, Algeria 20 000 7.3 1985 Mexico 25 000 8.1 1988 Armenia 25 000 6.9 1989 San Franscisco, USA 62 7.1 1990 North-west Iran 50 000 7.7 1995 Kobe, Japan 5 500 7.2

Prediction and Warning

Earthquakes cannot be predicted although areas most at risk can be identified. The buildings in these areas then can be modified to withstand earthquake shocks. For example, buildings constructed near the San Andreas fault in San Fransisco, have to meet extremely strict building regulations.

Biblical Accounts

Eze : 38:19

In my zeal and fiery wrath I declare
that at that time there shall be a great
earthquake in the land of Israel.

Rev: 6:12

I watched as he opened the sixth seal.
There was a great earthquake. The sun
turned black like sackcloth made of goat hair,
the whole moon turned blood red.

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