The intensity of an earthquake can be measured. One measurement is called the Richter scale. Earthquakes below 4.0 on the Richter scale usually do not cause damage, and earthquakes below 2.0 usually can’t be felt. Earthquakes
over 5.0 on the scale can cause
damage. A magnitude 6.0
earthquake is considered strong
and a magnitude 7.0 is a major
earthquake. The Northridge
Earthquake, which hit Southern
California in 1994, was magnitude 6.7.
Earthquakes often occur when tectonic plate collide
What happens when plates collide? It depends how the plates are moving when they meet:
When two plates collide head-on, they push each other up and form mountains. That's how the Himalayas and other great mountain ranges (including the Rockies, long ago) were created.