1. Scales and Forecasting
Earthquakes
Scales and Forecasting

2. Reverse Fault Compression force – Convergent boundaries
Pushes on rocks causing to bend and sometimes break
Rocks above fault are forced up and over rocks below fault line
Rocky Mountains

3. Strike-slip Fault (Transform)
Shear Force
No upward or down movement
Surfaces snag and rocks are twisted and strained due to friction
Short and sudden but can be slow and steady
San Andreas Fault

4. Magnitude & Intensity Damage caused by Earthquakes depends on…
Distance to Epicenter
Depth of Focus –How far underground the earthquake occurs.
Bedrock/Soil Types
# and types of structures located in the area

5. Magnitude vs. Intensity
– measured force based on seismic waves that travel through the earth
Measurable
Intensity
– What was felt?
-What occurred? Observer specific

6. Modified Mercalli Scale
Arbitrary set of definitions based upon…
What people in area feel when earthquake occurs - Deals with the Intensity
Their Observations of damage to buildings
Example:
Is the chimney broken?
Did the chimney totally fall over?
Where the windows shattered?
The scale is 1 to 12

7. Advantages Mercalli Scale
Great for use if happens in an inhabited area of developed country. (lots of people can describe damages)
Easy to use
Do not have to use specific equipment

8. Disadvantages of Mercalli Scale
No use in middle of desert or places without buildings and tree.
Observer specific – what appears to be “heavy” to one person may not be considered heavy for another.

9. Richter Magnitude Scale
Is the effects of any one earthquake varies greatly from place to place
May be many intensity values (e.g. IV or VII) measured for same E-Q
Each E-Q should have only one magnitude (e.g. 4.5 on the Richter scale)
Based on seismic waves travel through Earth
Deals mainly with the strength of the break,
How much energy is released by the E-Q
Tool to get an idea, Not Perfect

11. Richter Magnitude Scale
Allow us to compare earthquake magnitudes regardless of location
Good for small, nearby earthquakes
Used from 1930’s to 1980’s
It is logarithmic – metrics is comparable
Meaning that each whole number step represents a ten-fold increase in measured amplitude.
For example a magnitude of 7 E-Q is 10 times larger than a 6, and 100 times larger than a 5, and 1000 times larger than a 4.
With each increase of 1.0 , the energy release increases by 32 times.

12. Moment Magnitude Scale
Estimates the total energy released by earthquake
Good for all earthquakes
Measures size and type of waves and movement along faults
Movement gives us more information
When you hear “Richter” on the news, actually referring to Moment Magnitude Scale

13. Forecasting vs. Predicting
Forecasting – General statement about what will happen in future (not specific)
Forcast something will happen in the future (not specific)
We have the ability to forecast
Predicting – Specific statement with specific date
We do not have the ability to predict E-Q
Animal behavior – ground animals come out of ground
Radon Levels increase in ground water

14. Why are they so difficult to predict?
Many factors
Movement – don’t know when
Stresses
Rock mechanical property (brittle of elastic
Past movement – No History
Seismic gaps