EARTHQUAKES
BY MADDI JURY
WHAT IS AN EARTHQUAKE?
An earthquake (also known as a quake, tremble or tremor) is the shaking of the surface of
the Earth resulting from the sudden release of energy in the Earths lithosphere that creates
seismic waves. Earthquakes can range in intensity, from those that are so weak they cannot
be felt, to those that are violent enough to propel people and objects into the air, damage
critical infrastructure and wreak destruction across entire cities.
Seismic activity of an area is the frequency, type and size of earthquakes experienced over a
particular time period. The seismicity at a particular location in the Earth is the average rate
of seismic energy release per unit volume. The word tremor is also used for non-earthquake
seismic rumbling.
WHAT CAUSES EARTHQUAKES?
The tectonic plates that make up the Earth's crust are constantly moving. As the edges of
these plates slide against each other in fault zones, friction can slow them down, leading to
the build-up of pressure over long periods of time. When the force of movement finally
overcomes the friction, sections of the crust suddenly break or become displaced, releasing
the pent-up pressure in the form of seismic waves. This is a naturally occurring earthquake,
sometimes referred to as a tectonic earthquake.
While tectonic earthquakes can occur at any location around the world, the majority of
large earthquakes occur at the circum-Pacific seismic belt found along the rim of the Pacific
Ocean. Two other regions regularly exhibiting earthquakes include the Alpide belt extending
along the southern margin of Eurasia through the Himalayan Mountains, Sumatra, and Java;
and the Mid-Atlantic Ridge running along the floor of the Atlantic Ocean.
When an earthquake occurs, different types of energy waves are generated.

P WAVES Or primary waves are the first waves to be detected. These are
compressional waves that push and pull as they move through rocks and fluid.

S WAVES Or secondary waves are the next waves to be detected. These waves move
only through rock. They move up and down or side to side, perpendicular to the
direction in which the wave is moving.

SURFACE WAVES Follow P and S waves. They travel along the surface of the earth
and thus cause the most damage. Surface waves can be characterised as Love Waves
which are faster and move the ground from side to side, and Rayleigh waves, which
roll like waves on the surface of oceans and lakes.
Tectonic plates
WHAT OTHER TYPES OF EARTHQUAKES
EXIST?
In addition to tectonic earthquakes, seismologists have classified three more earthquake
types.

Volcanic: Earthquakes that occur in conjunction with volcanic activity.

Collapse: Smaller-scale earthquakes that result from the subterranean collapse of
caverns or mines.

Explosion: Earthquakes caused by underground explosions of nuclear or chemical
devices.
The energy of an Earthquake can be felt for many miles. The shockwaves can travel through
the surface of the earth, but they can also travel down through the layers of the earth
where they bounce off from matter inside the earth. Even following an earthquake,
aftershocks can repeat over and over for days or months. An aftershock is a smaller quake
which follows the original one but can still continue to cause damage to an already troubled
area of land. They usually decrease in size and frequency with time.
Earthquake shaking can cause much destruction and loss of life/ Th ground under buildings
can become loose and buildings can fall or sink. Rockslides can occur. Liquefaction, ground
displacement, flooding, Tsunamis, and fire are all hazards of earthquakes.
One of the greatest dangers is a tsunami. A tsunami happens when shocks from the
earthquake create huge waves that come inland and strike communities long the coast. In
the ocean tsunamis may only be 1 metre high and can be 90 miles apart. They can travel at
500mph. When they reach shallow coastal waters, they can grow to 35 metres high and
cause massive flooding. Satellites in space watch for tsunamis and transmit images to
scientists on Earth. These images help scientists better predict when, where, and how
strong a tsunami will be.
Building affected by an Earthquake
Village hit by a Tsunami