Bernadette Bolig, age 11, of Bow Island, Alberta, Canada, for her question:

WHAT IS THE RICHTER SCALE?

A Richter magnitude is a number that indicates the strength of an earthquake. Scientists calculate Richter magnitude by using information obtained from a seismograph, an instrument that records the ground motion of an earthquake.

An American scientist named Charles Richter developed this system in 1935, and the system is now sometimes called the Richter scale.

Each number on the Richter scale represents an earthquake 10 times stronger than the one of the next lower magnitude. An earthquake of magnitude seven is 10 times as strong as one of magnitude six. The Alaska earthquake of 1964 measured 8.4 on the Richter scale. Calculations based on instruments used at the time show the 1906 San Francisco measured 8.3