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Earthquakes
What are Earthquakes?
Earthquakes are
What are Earthquakes? As the plates move
they put forces on themselves and each other.
What are Earthquakes When the break occurs, the stress is released
as energy which moves through the Earth ______________________________________, which we feel and call an earthquake.
What causes the stress?
There are three main forces that drive deformation within the Earth and create the stress that causes earthquakes.
Which of the following things are elastic? Pasta Rubber bands Super balls Rocks Plastic Metal Dirt
Elasticity Elasticity is a physical property of materials
which return to their original shape after the stress that caused their deformation is no longer applied
What does that mean?
Elasticity
We can use the elastic properties of rock to explain how energy is stored and released within the Earth’s crust.
Elastic Rebound Explains how energy is stored
in rocks
Rocks bend until the strength of the rock is exceeded
Rupture occurs and the rocks quickly rebound to an undeformed shape
Energy is released in waves that radiate outward from the fault
More Stuff About Earthquakes
Faults Any stress on the plates can cause an
earthquake if the elastic limit is reached.
Each type of stress, however, results in a specific type of fault.
Normal Fault
=
Reverse Fault AKA Thrust Fault
=
Strike Slip
=
• No change in elevation, rock slides past one another.
Focus and Epicenter
Focus:
Epicenter:
Types of Earthquakes - Foci are less than 70 km
depth.
- Foci are between 70 and 300 km depth.
- Foci are greater than 300 km.
Measuring Earthquakes
How do we measure an earthquake? There are two main scales with which we can
measure an earthquake. Mercalli Richter
The Mercalli Scale In 1902 Guiseppe Mercalli devised a scale for
measuring the intensity of an earthquake by
In 1931 seismologists modified his scale to adapt to modern American building standards.
We can use Mercalli’s modified scale to find the epicenter of an earthquake.
I Barely felt
II Felt by a few sensitive people, some suspended objects may swing
III Slightly felt indoors as though a large truck were passing
IV Felt indoors by many people, most suspended objects swing, windows and dishes rattle, standing autos rock
V Felt by almost everyone, sleeping people are awakened, dishes and windows break
VI Felt by everyone, some are frightened and run outside, some chimneys break, some furniture moves, slight damage
VII Considerable damage in poorly built structures, felt by people driving, most are frightened and run outside
VIII Slight damage to well built structures, poorly built structures are heavily damaged, walls, chimneys, monuments fall
IX Underground pipes break, foundations of buildings are damaged and buildings shift off foundations, considerable damage to well built structures
X Few structures survive, most foundations destroyed, water moved out of banks of rivers and lakes, avalanches and rockslides, railroads are bent
XI Few structures remain standing, total panic, large cracks in the ground
XII Total destruction, objects thrown into the air, the land appears to be liquid and is visibly rolling like waves
The Richter Scale Prior to 1935 earthquakes were measured by
using the Mercalli Scale.
Charles Richter (1935) created a numerical method based on the __________________________________________recorded on a seismogram and the distance from the epicenter.
Richter Scale Richter magnitudes are based on a
logarithmic scale, base 10
This means that for each whole number you go up on the Richter scale the strength of the earthquake goes up ten times.
Magnitude Examples A magnitude of 3 is ____ times ____________
than a magnitude of 2 A magnitude of 5 is ____ times ____________
than a magnitude of 7 A magnitude of 6 is ____ times ____________
than a magnitude of 2
M1
M2
M3
So, what does it mean? Think of it in terms of energy released by
explosives: A magnitude 1 earthquake releases as much
energy as blowing up 6 ounces of TNT
A magnitude 8 earthquake releases as much energy as blowing up 6 million tons of TNT!
That is roughly 6 nuclear bombs!
Measuring Via Richter Scale What do we need to determine the size of
the earthquake? Seismograph
Determine the ________________________________________ Determine ___________________________________________ Determine ___________________________________________
Nomogram Find the S-P interval Find the amplitude Draw a line that connects the above points to find
magnitude
Example
Measuring Earthquakes
Waves Edition
Seismic Waves There are three types of waves that are
created when stress is released as energy in earthquakes
P-waves Primary waves are the fastest of the three
waves and the first detected by seismographs.
Move at about 3.5 miles/second
They are able to move through both liquid and solid rock.
P waves, like sound waves, are longitudinal waves, which means that they compress and expand matter as they move through it.
S-waves Secondary waves are the waves directly
following the P waves.
Move at about 2.1 miles/second
S waves move through solids only
Serpentine movement
Body Waves Both P and S waves are called body waves
because they move within the Earth's interior.
Surface WavesTravel just below or along the ground’s surface Most damaging waves!
Move at about 1.2 miles/second
Two Types: L – Waves R - Waves
Surface Waves L – waves, or Love Waves, move parallel to
the Earth's surface and perpendicular to the direction of wave propagation.
R – waves, or Rayleigh waves, move in an elliptical motion, producing both a vertical and horizontal component of motion in the direction of wave propagation.