Page 59 - How It Works - Book of Amazing Answers To Curious Questions, 12

---- Environment Q�
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What is the Rich scal
An earthquake's size can be calculated on the familiar
Richter scale, which makes use of logarithms for
comparing the scale of one earthquake to another, or
the more scientific Moment Magnitude scale, which
uses sophisticated seismology equipment to measure
an earthquake's actual energy.

CATASTROPHIC STRONGER
Richter magnitude: >8 Richter magnitude: 5
Moment magnitude: N/A Moment magnitude: 5.9
Affects areas thousands of miles Felt by everyone. Minor to moderate
across. Complete devastation damage caused
VERY DISASTUS STRONG
Richter magnitude: 8 Richter magnitude: 4
Moment magnitude: N/A Moment magnitude: 5.0
Damage over hundreds of miles. Felt by most people. Possible
Masonry destroyed, bridges down, damage occurs. Windows and
large cracks appear in the ground. crockery likely to break and trees
disturbed.
DISASTROUS
Richter magnitude: 7-8 MODERATE
Moment magnitude: N/A Richter magnitude: N/A
Moment magnitude: 4.9
Major damage to buildings caused
(masonry and frames destroyed). These are often felt indoors.
Ground subsidence, rails bent, pipes resulting in crockery being
broken, landslides possible. disturbed. Cracks may appear
�n walls.
VERY DESTRUCnYE
Richter magnitude: 7 SLIGHT
Moment magnitude: 7.0 Richter magnitude: 3
Moment magnitude: 4.0
Serious damage possible over large
areas. Structures and ground shifted Noticeable vibrations indoors.
DESTRUCnYE NEGLIGIBLE
Richter magnitude: 6 Richter magnitude: 2
Moment magnitude: 6.9 Moment magnitude: 3.9
Modere to major damage to t:uildings. Can be felt on upper floors in
Heavy fumrture moved around. tall buildings.
VERY STRONG INSTRUMENTAL
Richter magnitude: 5-6 Richter magnitude: 2
Moment magnitude: 6.0 Moment magnitude: 1.0-3.0
Possible structural damage to A microearthquake detected
buildings in populated areas. Noticed by instrumentation. Barely felt
by people driving by humans.
more powerful than a magnitude two. Quite an than urban areas built on loose debris and drops over time. However they can happen
unimaginable thought. sediments. Water-saturated sediments can months, years or decades after the quake.
It's interesting to note that earthquake damage behave like quicksand when shaken, where loose Undersea earthquakes can be as devastating as
isn't directly related to magnitude. Deep, distant grains move apart and flow like a liquid. In those on land, if not more. Fault movements can
earthquakes shake the ground less than close, Niigata, Japan, 1964, earthquake-resistant displace huge volumes of water, which crash to
shallow earthquakes because the energy released buildings tumbled onto their sides when the shore as killer waves called tsunamis. An undersea
at the focus has had a chance to disperse. Big ground underneath liquefied. The population earthquake near northern Indonesia triggered the
earthquakes often cause longer tremors. For faces additional hazards once the shaking stops. Indian Ocean tsunami in 2004-the world's biggest
example, an earthquake in for at leasqoyears. At least
1949, which had a magnitude Unstoppable and terrifying, big quakes 120,000 people in Indonesia
of 7.1, shook the ground for 30 alone were killed by the giant
seconds, while a magnitude strike with little or no warning waves. Rescue teams cleared
8.3 earthquake in 1964lasted up bodies for weeks
five minutes. Fires break out where the ground convulsions afterwards. The final death toll was over 2oo,ooo.
The majority of the shuddering during an sever gas and electricity lines or destroy Tsunamis can reach speeds of 970 kilometres
earthquake is caused by Rayleigh waves. These flammable objects. Nearly 90 per cent of the per hour in the deep ocean, depending on water
surface waves roll along, convulsing the Earth's damage in the 1906 San Francisco earthquake was depth. As the tsunami races into shallower water,
crust. The ground heaves up and down and from due to fire. Lives can be endangered and rescue it slows down and can reach a mammoth 3om high
side to side much like water waves in the ocean. efforts thwarted by collapsed bridges, burst water when it hits shore. The first sign may be water
Earthquakes can shake the ground violently pipes, broken containers ofhazardous chemicals rushing out to sea, sometimes beyond the horizon,
enough to open large fissures but, unlike in the and aftershocks. leaving the sea floor bare. The sea pours back
movies, these don't crunch closed around people's Aftershocks are the less powerful earthquakes onshore as a series of towering waves or a rapidly
bodies and legs. following the main tremor, when faults shift and rising tide. Warning signs such as these can save
Big, long-lasting surface waves created by large readjust after the release of energy and stress. You lives. A ten-year-old British girl saw the sea
earthquakes can topple buildings, crack roads could think of a tremor as the ground breathing a hurtling away from the beach at a resort in Phuket,
and buildings and even trigger landslides. big sigh of relief. Major earthquakes are usually Thailand in 2004and warned her mother and staff
Well-built, earthquake-proofbuildings on solid followed by several noticeable aftershocks within that a killer wave was coming. She'd learned about
bedrock usually suffer substantially less damage the first hour or so. The number of aftershocks tsunamis in school a fortnight before.

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