Some 80 percent of all the planet's earthquakes occur along the rim of the Pacific Ocean, called the "Ring of Fire" because of the preponderance of volcanic activity there as well. Most earthquakes occur at fault zones, where tectonic plates; giant rock slabs that make up the Earth's upper layer; collide or slide against each other. These impacts are usually gradual and unnoticeable on the surface. However, immense stress can build up between plates. When this stress is released quickly, it sends massive vibrations, called seismic waves, often hundreds of miles through the rock and up to the surface. Other quakes can occur far from faults zones when plates are stretched or squeezed.
Scientists assign a magnitude rating to earthquakes based on the strength and duration of their seismic waves. A quake measuring 3 to 5 would be considered minor or light; 5 to 7 is moderate to strong; 7 to 8 is major, and 8 or more is great.
California Seismograph Activity
We've been touring Since 1999. TCP# 12932 (Last update July 2011.)