Evaluating Earthquakes

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.

Earthquake Causes

Describe what is happening at each step. At which step does the

earthquake occur?

1.

2.

4.3.

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, but in new positions relative to each other.

What if the street depicted in 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 Richter Scale point bigger releases 32 times the amount of energy.

y = 10xy = 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

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?

On a separate sheet of paper, write and answer the following questions: