Transcript Earthquakes 3 Evaluating Earthquakes

Evaluating Earthquakes
Earthquake Causes
Rare:
• Volcanic Eruption
• Cave Collapsing
• Meteor Strike
Common:
• The release of stress built up from two or
more tectonic plates moving past each other.
• This is called the Elastic-Rebound Theory.
Describe what is happening at each step.
At which step does the earthquake occur?
1.
2.
3.
4.
Elastic Rebound Theory
1. Friction and stress build up between two
plates trying to move past each other.
2. The stress deforms both plates.
3. Eventually the stress becomes too great.
Rocks at the interface (fault) give way, and
the plates suddenly move.
4. The plates go back to their former shapes,
What
if
the
street
depicted
in
but in new positions relative to each other.
this animation was a river?
Elastic Rebound Theory
The river will alter its course!!
Was the first capital of
Illinois (1818-1819)
Was a major center of
commerce.
Was an economic rival of
St. Louis until 1881.
An earthquake in 1881
cause a ground shift and
flooded the city.
Earthquake Strength
The strength of an
earthquake is measured
against the Richter Scale.
The Richter Scale:
• starts at above zero,
• has no upper limit,
• commonly uses values
above 2 and below 10.
Earthquake Strength
The Richter Scale directly measures the
amplitude of seismograms. The bigger the
squiggle, the stronger the quake.
Since seismographs that are closer to the
epicenter will record higher amplitudes, each
seismogram is corrected for distance (100km).
The bigger the squiggle, the closer the quake.
Earthquake Strength
An earthquake with an amplitude 10 times
bigger is rated one Richter Scale point stronger.
An earthquake one
y Richter
= 10x Scale point bigger
releases 32 times the amount of energy.
y = 32x
Earthquake Strength
Earthquake Strength
How would you describe
the damage in each
picture?
Which one is worst?
How do earthquakes
affect people (as many
ways as possible)?
Earthquake Strength
The Mercalli Scale:
A scale that describes the
intensity/severity of an
earthquake’s effect.
It uses Roman Numerals I
through XII.
That’s 1 through 12 in
Arabic Numerals.
Evaluating Earthquakes
On a separate sheet of paper, write and answer
the following questions:
1. Describe the similarities and differences
between the Mercalli and Richter scales.
2. Detail any reason why one scale would be
preferred by the public when hearing news
of an earthquake.
3. Would the scientific community prefer the
same scale as the public? Why or why not?