Earthquake measurement:

A seismometer / seismograph is the instrument used to measure and record earthquakes. When the ground moves, the instrument placed on it also moves, however the cable and weight attached do not. This produces a record called a seismogram on a rotating drum. There may be 3 different recordings on ground movements:

A) East to West Horizontal
B) North to South Horizontal
C) Vertical

Portable seismographs are used to monitor the aftershocks of major earthquakes or to measure tremors during a volcanic eruption. Modern observatories place seismographs deep in the ground in remote places far from confusing signals like heavy traffic or quarrying. The data is transmitted via telephone lines.

TWO SCALES ARE USED TO DESCRIBE THE STRENGTH OF AN EARTHQUAKE

Richter scale --> This scale measures the intensity/magnitude of an earthquake, (the energy released when it occurs).This scale is from 1 -10. It is logorythmic which means that each unit on the scale is 10x more powerful than the one before it. Anything below 2 is described as a microquake because it goes undetected to a normal person. Moderate quakes measure less than 6. More than 6 can cause significant damage. It is an open-ended scale. The strongest earthquake ever took place in Chile in 1960. It measured 9.5 on the Richter Scale.

Modified Mercalli scale --> This measures damage on a 12 point scale. 1 means no damage and 12 indicates complete destruction. This scale is generally not used because the level of damage caused by a similar quake can differ between developed and developing countries.

	Created by eimearkelly3 almost 11 years ago

notes on earthquakes, with videos

The Geography Of Earthquakes