Last week on **March 11, 2011 a powerful earthquake** occurred with an epicenter 80 miles off the coast of Japan **near the city of Sendai,** which has a population of about one million people. The *Clear Science staff* has heard the magnitude of the Sendai earthquake reported from **8.8 - 9.0** on the **moment magnitude scale (MMS)**. The MMS is similar to the **Richter scale**, a name which is still sometimes used colloquially. (And why not? People know what it means!)

The **MMS is a logarithmic scale**, meaning that **each number higher is actually ten times more powerful in magnitude**. That’s why a big truck going by your house might be a 3-4 on the scale, but a huge earthquake that results in massive loss of life will be an 8 or 9. The largest earthquake ever recorded on Earth was the **1960 Valdivia earthquake in Chile**, which was a 9.5. If you run through the logarithm math, this is **3.2 times larger** than the Sendai earthquake that just happened.

The measurement scale for **sound pressure**, **decibels**, is also a logarithmic scale, in which small changes in number signal huge changes in loudness. (Decibels or dB are actually a logarithm multiplied times 20, so every 20 is 10x higher.)