Earthquakes
Earthquakes are sudden rapid vibrations of the earth’s crust. It is usualy what happens when two blocks of
the earth suddenly slip past one another or break apart from each other. The fractures on the surface of
the earth caused by the earthquake are called faults.
The hypocentre is the spot beneath the earth’s surface where an earthquake originates, from this spot the
vibrations move up towards the surface. The epicentre is the spot on the earth’s surface above the
hypocentre where the earthquake is felt first, from here the vibrations spread to the surrounding areas.
When the epicentre is under the sea the earthquake is called “tsunami”. The vibrations are called seismic
waves and there are two types: primary waves ( P waves) are longitudinal in nature and are faster than
secondary waves ( S waves) which are transversal.
Unfortunately earthquakes cannot be predicted but most of the world’s earhquakes occur along the Ring
of Fire which is the costal belt of the Pacific Ocean.
Earthquakes are measured with a seismograph and there are two scales to measure the intensity of the
earthquake: the Mercalli scale and the Richter scale ( named after the seismologists who created them).
The Mercalli scale measures the effects of an earthquake on human buildings and its landscapes. There are
12 intensities, 1 is the lowest and 12 is the highest.
The Richter scale measures the eartquake’s magnitude ( the energy released). Currently the maximum
magnitude registered is 8,7 which corresponds to the highest intensity of the Mercalli scale: total
destruction and ditortion of the ground.
Answer the questions:
What is an earthquake?
Write the definitions of : fault – hypocentre – epicentre.
What is a tsunami?
How can we measure earthquakes?
What is the difference between the Mercalli scale and the Richter scale?
In the past there have been many terrible earthquakes, choose one and write what happened. ( San
Francisco, Haiti, L’Aquila....)
Earthquakes
Earthquakes are sudden vibrations on the Earth’s crust.
An earthquake originates in the hypocentre under the earth’s surface and the
epicentre is where we feel the eartquake on the surface. When the epicentre is
under the water the earthquake is called “tsunami”
Seismologists measure earthquakes with a seismograph.
There are two scales to measure earthquakes:
 The Mercalli scale: there are 12 intensities and it measures the visible effects
of an earthquake
 The Richter scale: measures the magnitude (energy) of the earthquake and
the maximum level up to this moment is 8,7.
Match the word and the definition
hypocentre
A sudden movement of the
earth’s crust
Mercalli scal
Where we feel the earthquake on
the surface of the earth
Richter scale
Epicentre
Seismograph
The point where the earthquake
originates under the surface
Measures the effects of an
earthquake
Earthquake
Measures the energy o fan
earthquake
We use this to measure an
earthquake.