earthquakes – the shaking of the ground caused by the release of energy waves as rocks in the...
TRANSCRIPT
EARTHQUAKES
DEFINITION Earthquakes – the shaking of the ground
caused by the release of energy waves as rocks in the earth’s crust move suddenly
Seismology – The study of earthquakes Seismologist – Scientists who study
earthquakes
WHERE DO EARTHQUAKES OCCUR? Near edges of tectonic plates Tectonic plates can move toward each
other, away from each other or slide past each other
These movements create faults in the Earth’s crust
A fault is the break in the Earth’s crust along which blocks of the earth's crust slide
Earthquakes occur along these fault lines
WHAT CAUSES EARTHQUAKES? As tectonic plates move along faults,
stress builds up as the rocks get stuck together
This causes the rocks along the fault to change their shape or deform
Elastic deformation leads to earthquakes Rocks can stretch but eventually they will
unstick and move suddenly into a new position
When the rocks unstick they release energy in the form of seismic waves. These waves of energy cause earthquakes
SEISMIC WAVES Waves of energy that are released
during an earthquake. These waves are able to travel through
the Earth’s interior and along the Earth’s Surface
It is these waves that cause damage during an earthquake
P AND S WAVES P Waves are the fastest seismic waves
Also known as Primary WavesThey are able to travel through both liquids
and solids so they can reach across the entire planet
S Waves travel at half the speed of P WavesAlso known as Secondary WavesThey can only travel through solids so they
can not travel through the Earth’s outer core
LOCATING AN EARTHQUAKE Seismologists use seismographs. These
instruments can detect and record seismic waves
Based on the arrival times of P and S waves to the seismograph, seismologists can determine the location of the earthquake.
EPICENTER AND FOCUS Epicenter is the point on the Earth’s
surface directly above an earthquakes starting point
Damage done during an earthquake will usually be the most severe at and around the epicenter
Focus is the point inside the Earth where an earthquake begins
Seismographs and the timing of the S and P waves can help to locate the epicenter and the focus of an earthquake
MEASURING STRENGTH AND INTENSITY Strength of an earthquake is measured
using Richter Scale Strength also known as magnitude Measure of ground motion Based on a scale of 1 to 10 Each unit increase equals ground motion
becomes 10 times larger Intensity of an earthquake is measured
using Mercalli Scale Measure of how people feel the earthquake and
how much damage it causes Based on numbers I to XII I is not felt at all, XII is total damage to area