Page 58 - How It Works - Book of Amazing Answers To Curious Questions, 12

AMAZIG ANSWERS TO CURIOUS QUESTIONS -------------------

Nonnal fault Reverse or Mountains Split river
The rock slab lying above thrust fault Thrust faults are common in This river basin has been split
the sloping fault line slides Slabs lying above the huge mountain ranges like the in two by the rock slabs on
downwards as the plates sloping fault line lift up Himalayas, where two either side of the fault,
separate. You get the same along a reverse fault. Plate continental plates are colliding. moving in opposite directions.
effect removing the collisions push a rock slab
bookend from a shelf of up and over another along
sloping books. a thrust fault. Plates sliding
horizontally
Crustal plates can
slide past each other,
causing straight
cracks called
strike-slip faults. The
two plates move
horizontally in
opposite directions
along the fault line.

Basins and ranges
Steep mountain ranges and flat
valley basins form where rock
blocks are lifted and lowered by
normal faulting. Death Valley,
California in the western United
States is a good example.

Plates moving apart Plates colliding
Crustal plates are moving apart Crustal plates are colliding, putting
fracturing the Earth's brittle pressure on the Earth's crust. As the
crust along fault lines - cracks plates slowly crunch together, the
where slabs of broken rock grind crust bends, folds and fractures like a
past each other. car bonnet in a crash.

What causes

How a sudden release of
pressure flattens cities and
earthqual<es? spawns tsunamis

ven if you've never felt an earthquake, places, they collide or are pulled apart. Faults The released energy speeds through the Earth
you'll know they can be devastating. Films break open as these rigid plates move and exert in the form of shock waves. There are three main
Elike 2012 feature 'mega quakes', where forces great enough to crush and tear solid rock. types of shockwave: primary, secondary and
gaping fissures swallow people and buildings. As the plates move about, the rock slabs at surface waves. Primary waves radiate fastest from
Real-life earthquakes are less dramatic than either side of fau Its are dragged past each other. the earthquake focus. Secondary waves arrive
those in the movies, but they're still one of But rocks are jagged and uneven, meaning there's later and surface waves arrive last. The surface
nature's worst natural hazards. Unstoppable and lots of friction between them. This friction causes waves travel near the Earth's surface, rocking the
terrifying, big quakes strike with little or no the rocks to become locked together. Pressure ground and causing the widespread devastation
warning, flattening cities and killing tens of builds along the fault as the plates grind along, wrought by the largest earthquakes. People
thousands of people. squeezing and stretching the rocks until, barely feel primary or secondary waves.
Most of the world's earthquakes occur at the eventually, they break and lurch forward. Huge The size of an earthquake is defined by its
boundaries between the Earth's huge crustal amounts of pent-up energy are unleashed, and it's magnitude-this is a measure of the energy
plates. These boundaries are called faults, and the resulting snap that is an earthquake. released. Magnitude isn't a simple measurement
the plates-of which there are 15 of varying The point at which the Earth's crust first breaks of the relationship between earthquake size and
different sizes here on Earth-jostle on the is called the earthquake focus. This is usually energy. Increasing the magnitude by one
planet's surface like the pieces of a giant, floating many miles below the Earth's surface. The increases shockwave size by ten times and total
jigsaw puzzle. In some parts of the world, these epicentre is the point on the surface located energy released by about30 times. So for example,
crustal plates grate past each other. ln other directly above the focus. a magnitude eight earthquake is a billion times

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