1. Magnitude verses Intensity!
Earthquake Strength
Magnitude verses Intensity!

2. Magnitude
Is a measure of the amount of energy released from an earth quake.
Recorded by the amplitude of the highest S wave
There is only one magnitude for each earthquake – but we still use 3 seismograms to calculate it
Magnitude of earthquakes is measured by the Richter scale or Moment Magnitude

3. Richter scale – developed by Charles Richter in 1930

4. 31.7 times more energy released and 10 times stronger for every unit increase on the Richter scale

5. How is this magnitude calculated?

6. Moment Magnitude The measure of total energy released by an earthquake
Preferred by seismologists because it is more precise
Based on the area of the fault ruptured in the quake instead of just the epicenter
Calculated by multiplying the area of the fault’s rupture surface by the distance the earth moves along the fault

7. Earthquake Intensity
A number describing the severity of an earthquake in terms of it’s effects on the earth’s surface, human beings, and structures such as buildings – Basically the impact the earthquake causes!
Measured by the Mercalli Scale

8. Mercalli Scale

9. The Mercalli scale helps create “Isoseismic Maps”

10. Maps that shows how often and how strong

11. Can we predict Earthquakes?

12. Warning Signs
Average temperature of the area keeps increasing – a few months prior to an earthquake
A sudden rise or fall in water levels
Seismo-electromagnetic precursor – (10-20 hours prior) geomagnetic field is reduced which affects radio, tv, telephone, and cell phones
Animals highly disturbed and restless
Sensitive patients may experience an increase in blood pressure, migranes, heart trouble

13. Seismic gaps
A zone along a tectonically active area where no earthquakes have occurred recently, but it is known that elastic strain is building in the rocks
If identified it might be an area expected to have a large earthquake in the future

14. Seismic Gap
In this illustration you can see areas of earthquake activity and an area of non activity – the area of non activity represents a “seismic gap”
Notice this is a subduction zone between two tectonic plates.

15. The Gap Hypothesis
Parts of active faults that have had relatively few earthquakes are likely to be the sites of strong earthquakes!

16. San francisco Bay Area
A major seismic gap area of interest to scientists in the United States

17. Assignment
Mercalli Scale/isoseismic map activity