When earthquakes are reported, their intensity is given a number on the Richter Scale. What is the Richter Scale and what are real life comparisons?

In the 1850s, the seismograph was first invented. This device measures vibrations. Of course, early models were very inaccurate and only gave approximations of the vibration they felt. As time progressed, equipment became more and more accurate. So while we are very sure of recent readings, we are less sure of readings made in early days.

Charles Richter invented the Richter Scale in 1935 while working at the California Institute of Technology. Until this point, earthquakes were "measured" by describing how much destruction they caused. The Richter Scale was a much more objective measurement of the vibrations of the earth.

The Richter Scale is logarithmic. That means that the difference between 1.0 and 2.0 is not the same amount as the difference between 2.0 and 3.0. When you go from 1.0 to 2.0, 2.0 is ten times more powerful than 1.0 was. When you go from 2.0 to 3.0, 3.0 is ten times more powerful than 2.0 was. So 3.0 is actually *100 times* more powerful than 1.0 was. The power becomes more and more vast as you work your way up the scale.

The Richter Scale goes from 0, with no vibration at all, to 10, which is higher than any known earthquake.

0 - no vibration
1 - microquake, not felt by humans
2 - only machines would detect this level of vibration
3 - minor
4 - humans would feel a tiny bit of movement
5 - buildings would shake a small bit, maybe shift
6 - strong shake, some weak buildings might collapse
7 - very powerful - the San Fran earthquake was 6.9
8 - well built buildings destroyed - the 1906 San Fran earthquake was 8.2
9 - ground itself is moving violently
10 - massive upheavals