1. 7.3 Measuring and Predicting Earthquakes
The Way Tectonic Plates Move

2. Learning Targets: Locate earthquakes – epicenter and focal point
Explain how the release of energy of various types of earthquakes relates to magnitude, P and S waves
Predict the locations of earthquakes and faults (strike- slip, reverse and normal) based on soil, geological, or topographical maps.
Relate fault locations/types to plate boundaries
Explain precautions that can be made to protect life from earthquakes

3. Measuring Earthquakes
Seismometer: detects and records seismic waves
Must be firmly attached to the ground
Why?
A device used to measure seismic waves is called a seismometer. Look at the Root word List 4.

5. Seismometers Three seismometers needed to measure all the shaking
1 for vertical movement
2 for horizontal movement in perpendicular orientations
Rolling waves compared to side to side waves

7. Horizontal

8. Verticle

10. Seismograms Seismogram: written record of an earthquake
Read from left to right
Order of arrival always the same
P-waves
S-waves
Surface waves

11. Seismograms Seismograms calculate
Location of epicenter
Magnitude (strong)
Data from hundreds of stations is compared for added precision and accuracy

12. Locating the Epicenter
Each seismogram can tell the distance to the epicenter
But direction is uncertain
How many seismograms does it take to find the epicenter?
Three seismograms can give exact location

13. Locating the Epicenter
P-waves and S-waves travel at known speeds
Difference in arrival times shows how far away the earthquake was

15. Earliest time is left, later time is right

17. How many seismograms are needed in order to pinpoint the epicenter of an earthquake? 3

21. Calculating Magnitude
Magnitude: energy released by an earthquake
Based on the amplitude of the seismogram and distance from the epicenter
Skip slide

22. Intensity vs. Magnitude
Intensity: amount of shaking and damage
Differs from place to place depending on soil type and population density
Magnitude: amount of energy released by an earthquake
Helps compare earthquakes
Not useful in determining damage or death toll
The amount of shaking and damage done by an earthquake is the intensity.
The amount of energy released by an earthquake is called the magnitude.

23. Mercalli Scale Ranges from I-XII (1-12) Intensity (not magnitude) Good
Reports actual damage done
Very practical for risk assessment
Bad
Subjective
Differs from place to place e.g. Chile/Haiti
Intensity is the amount of shaking and damage done during an earthquake.

27. Magnitude Scales Richter Scale: energy released in a single point
Moment magnitude: energy released along entire fault
The total energy released by an earthquake along its entire fault is measured on the moment magnitude scale.

28. How magnitude and distance is calculated.

29. Large Spike
Far
Small Spike
Near

30. Magnitude Scales Moment magnitude is the modern scale
Similar to Richter, but measures power and size of fault

33. Earthquake Prediction
Easy to predict where
Hard to predict when and what magnitude (or how strong)
Which of the following are seismologists successfully able to predict? Where an earthquake is likely to occur.

34. Earthquake Prediction
Long term risk factors
Along plate boundaries
Seismic Gap: moved less than rest of fault
Short term risk factors
Foreshocks
Ground tilting
Unknown
When
Many small quakes or one large quake
Long and short term risk factors for living in that area.
Why are there usually no evacuations right before an earthquake? Nobody knows when an earthquake is going to occur so there is no time for evacuation.

35. Seismic Gap
A seismic gap is a section of a fault that has produced earthquakes in the past but is now quiet. For some seismic gaps, no earthquakes have been observed historically, but it is believed that the fault segment is capable of producing earthquakes on some other basis, such as plate-motion information or strain measurements

36. 7.4 Staying Safe In earthquakes

37. Long Term Earthquake Safety
Buildings can be built to move independently of the ground
Masonry can be reinforced with steal
Soft soils can be left to low density development
Emergency plans can be made
Monitoring and warning systems put in place

38. Short Term Earthquake Safety
Gas companies and mass transit systems can benefit from a few seconds warning
Beaches cleared before tsunami impact
People take shelter

40. Global Seismic Risk