YEAR 10 GEOGRAPHYPLATE TECTONICS

3. EARTHQUAKES

EARTHQUAKESFloating plates do not sound too harmful.But when the plates come together you can get earthquakes.

EARTHQUAKES OCCUR AT…… Destructive or Conservative plate margins.

STEP 1As two plates move towards each other, one can be pushed down under the other one and into the mantle.If this plate gets stuck it causes a lot of strain in the surrounding rocks.Sideways-moving plates can also get stuck.

STEP 2When this tension in the rocks is finally released it produce strong shock waves known as seismic waves. This is called an earthquake.

STEP 3The shock waves spread out from the focus – the point where the earthquake starts.

STEP 4The epicentre is the point on the Earth’s surface immediately above the focus. Near the epicentre, the waves are stronger and cause more damage.

THE RICHTER SCALEThe size or magnitude of an earthquake is measured using a seismometer; a machine with a seismograph on a revolving drum.Earthquakes vibrations are recorded by a sensitive arm with a pen at the end which moves up and down.

ENERGY RELEASEDThese readings are measured using the Richter Scale for energy released, which is an open-ended scale.This is a logarithmic scale, which means that an earthquake with a measurement of 5 is ten times more powerful than one with a measurement of 4.Most serious earthquakes are in the range of 5 to 9. The earthquake in 1906 was the most powerful recent one, with a value of 8,6.

CASE STUDY

1977 EARTHQUAKE IN ROMANIATHE NOISE

7.2 RICHTER SCALEThe 1977 Vrancea earthquake occurred on Friday, 4 March 1977, at 21:22 local time, and was felt throughout the Balkans. It had a magnitude of 7.2, making it the second most powerful earthquake recorded in Romania in the 20th century. The epicenter was situated in the Vrancea Mountains, the most seismically active part of Romania, at a depth of 94 km.The earthquake killed about 1,578 people (1,424 in Bucharest) in Romania, and wounded more than 11,300.

DAMAGESAbout 32,900 buildings were damaged or destroyed.Immediately after the earthquake, 35,000 families were without shelter. The economic losses are believed to have been as high as two billion US dollars.Most of the damage was concentrated in Romania's capital, Bucharest, where about 33 large buildings collapsed. Most of those buildings were built before World War II, and were not reinforced. After the earthquake, the Romanian government imposed tougher construction standards.

LARGEST EARTHQUAKE RECORDEDThe world's largest earthquake with an instrumentally documented magnitude occurred on May 22, 1960 near Valdivia, in southern Chile. It was assigned a magnitude of 9.5 by the United States Geological Survey. It is referred to as the "Great Chilean Earthquake" and the "1960 Valdivia Earthquake."The United States Geological Survey reports this event as the "largest earthquake of the 20th Century." Other earthquakes in recorded history may have been larger; however, this is the largest earthquake that has occurred since accurate estimates of magnitude became possible.

Great Chilean Earthquake