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EXTENSION
Name: _______________________________________________
Course: _____ Date: _______
PHOTOCOPIABLE MATERIAL
/ © Oxford University Press España, S. A.
Geology 1.º ESO
Read the following text and answer the questions:
SEISMIC WAVES HELP US UNDERSTAND THE EARTH’S INTERIOR
Seismic waves are produced during a seismic movement or earthquake. They travel through the Earth
from the hypocentre in all directions, and at different speeds depending on the type of materials that
form the internal layers that they have to travel through and the density of these.
There are different types of seismic wave: some travel through the inside of the Earth, such as P
waves and S waves; others are superficial and travel over the surface, such as L waves – the most
dangerous. L waves are responsible for the material damage in inhabited areas.
Seismic waves can be detected by seismographs. These devices record the speed on graphs called
seismographs, which are used to construct a speed graph of seismic waves at different depths inside
the Earth’s interior. These graphs can give us an idea of the structure of the Earth’s interior.
1.
At what depths do we observe sudden changes in the speeds of seismic waves?
2.
To which areas do you think that these changes in speed correspond? What names are they given?
