Planethopia

Earthquakes occur when two tectonic plates move suddenly one against each other. The rocks breaks underground at hypocenter and the earth shakes. Those waves spread to epicenter, point on the Earth surface above hypocenter. If a earthquake occurs under the sea it can cause a devastating tsunami.

Charles F. Richter invented scale for measuring an earthquakes in 1934. The Richter magnitude is measured from the amplitude of the largest seismic wave recorded by the earthquake, regardless of the type of strongest wave.

The Richter scale is logarithmic scale (base 10). This means that each whole number you go to the Richter scale, the amplitude of the ground motion recorded by seismograph goes up ten times. Using this scale, the earthquake of magnitude 7 would be ten times the level of ground vibration under earthquake of magnitude 6 (and 32 times more energy is released). A magnitude 8 earthquake releases as much energy and detonation of 6 million tons of TNT. Pretty impressive, is’n it? Fortunately, most of the earthquakes that occur each year are magnitude 2.5 or less, not enough for that most people to feel it.

The Richter magnitude scale is designed to describe small magnitudes earthquakes and they are expressed in negative numbers. This scale also has no upper limit, so it can describe earthquakes of unimaginable and (so far) unexperienced intensity, such as magnitude 10, 11 and above.

Another scale used to measure the strength of earthquakes is Mercalli scale. It was invited in 1902. by Guiseppe Mercalli and main difference between those two scales is that Mercalli scale uses observations of people who experienced the earthquake. This scale is not yet considered as scientific as the Richter, though.

The Mercalli scale isn’t considered as scientific as the Richter scale, though. Some witnesses of the earthquake might exaggerate just how bad things were during the earthquake and you may not find two witnesses who agree on what happened; everybody will say something different. The damage caused by the earthquake may not accurately show how strong it was because building design. distance from the epicenter and type of material the buildings rest on may significaly change level of destruction.

Magnitude of earthquake:

• less than 3.5 – generally not felt but recorded
• 3.5 to 5.4 – often felt but rarely causes damage
• less than 6.0 -  can cause slight damage
• 6.1 to 6.9  – can be destructive in area of 100km
• 7.0 to  7.9  – can cause serious damage over large areas
• 8 or greater can cause serious damage in areas several hundred km across

Picture below shows places on earth where some earthquakes occurred during the past.

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