Changes

Earthquakes are a significant natural [[hazard]] to populations living in areas prone to them, and emergency responses to the hazard vary with economic development. The most powerful and destructive earthquakes occur at tectonic plate boundaries like the [[San Andreas Fault]].

Earthquakes are a significant natural [[hazard]] to populations living in areas prone to them, and emergency responses to the hazard vary with economic development. The most powerful and destructive earthquakes occur at tectonic plate boundaries like the [[San Andreas Fault]].

The severity of earthquakes is measured using the [[Moment Magnitude scale]], which replaced the [[Richter scale]] with the largest quake ever recorded being 9.5 which struck Chile in 1960<ref>http://earthquake.usgs.gov/earthquakes/world/10_largest_world.php</ref>. The [[Mercalli scale]] has also been used to measure earthquakes.

The severity of earthquakes is measured using the [[Moment Magnitude scale]], which replaced the [[Richter scale]] in the 1970s. The largest quake ever recorded had a magnitude of 9.5; it struck Chile in 1960<ref>http://earthquake.usgs.gov/earthquakes/world/10_largest_world.php</ref>. Technically the Moment Magnitude scale only measures the absolute magnitiude; the [[Mercalli scale]] is used to measure the felt magnitude - essentially how much the ground shakes over the epicentre of the quake..