ON SHAKEY GROUND

ON SHAKEY GROUND

 

        Hundreds of tremors happened in different parts of the world every day, and many people have experienced them. Some found themselves at the center of major earthquakes. This can be a terrifying experience. Inside buildings, ceilings collapse, furnitures are tossed around, and windows shatters. Outside, the grounds heave violently. Trees and telephone poles fall. Pipes, drains, and electrical wirings are torn apart.

        Just how badly a quake hits depends on its magnitude, how deep the source (hypocenter), and how far the distance (epicenter) from you. The hypocenter is where the quake begins, usually when huge rocks suddenlyshift along a fault line. The epicenter is the point on the Earth’s surface directly above the hypocenter. As shock waves spread out from here, they decrease in strength. The effects of the earthquake also depend on the type of ground it hits. Strong bedrock can resist shaking, but soft. loose ground shakes violently and may turn into a muddy liquid, a process called liquefaction.

Magnitude	Average number per year	Modified Mercalli Intensity	Description
0 – 1.9	>1 million	—	Micro – not felt
2.0 – 2.9	>1 million	I	Minor – rarely felt
3.0 – 3.9	Around 100,000	II – III	Noticeable – noticed by a few people
4.0 – 4.9	Around 10,000	IV – V	Light – felt by many people, minor damage possible
5.0 – 5.9	Around 1,000	VI – VII	Moderate – felt by most people, possible broken plaster and chimneys
6.0 – 6.9	Around 120-150	VII – IX	Strong – damage variable depending on building construction and substrate
7.0 – 7.9	Around 15	IX – X	Major – wide-spread damage, some buildings destroyed
8.0 – 8.9	about 1	X – XII	Great – extensive damage over broad areas, many buildings destroyed
9.0 and above	< 1	XI – XII	Extreme – massive and extensive damage over broad areas, most buildings destroyed

 
(The article On Shaky Ground and the accompanying illustrations, re-published with editing from Reader’s Digest: Earthquake and Volcanoes, 2000, p. 22-23).