1. Faults and Earthquakes

2. Learning Goals By the end of this lesson students will be able to:
Investigate the main types of seismic waves and its movement through rocks
Locate the epicentre of an earthquake, given the appropriate seismographic data
Compare qualitative and quantitative methods used to measure earthquake intensity and magnitude
Evaluate the accuracy and reliability of technological methods of monitoring and predicting earthquakes

3. Key Points Forces Within Earth Seismic Waves Locating Earthquakes
Measuring Earthquakes
Earthquakes and Society

4. Earthquakes Predominantly occur at:
Plate boundaries, along faults which are cracks in the earth where plates are moving in different directions (compression, tension, shear)
As plate bump into and slide past each other rocks catch on one another.
The stress in the rock builds up until it breaks causing an… EARTHQUAKE!

5. Types of Faults
Faults are classified according to the kind of motion that occurs along them

6. Focus- the spot within the Earth where the fault rupture actually occurs; location of the earthquake
Epicentre- the location directly above the focus on the surface of the Earth
Earthquake Occurs
The depth of the focus can be categorized as:
Shallow (up to 70 km below the surface)
intermediate (70 to 300 km)
Deep (greater than 300 km)

7. Seismic Waves How Seismographs Work
Earthquakes generate seismic waves that travel through the earth
P waves can pass through a liquid and rock.
S waves Can only pass through rock
Surface waves produced when P and S waves reach surface
Primary waves
Secondary waves- named with respect to their arrival times after P-waves
Slowest is Surface

8. Locating Earthquakes
Seismograph is an instrument that record the motions of the earth
Seismic waves produced from earthquakes are recorded
Epicentre locations can be determined using seismograms and travel-time curves.

9. Measuring Earthquakes
Scientists have developed several methods for describing the size of an earthquake

10. Magnitude and Intensity
Intensity- How strong earthquake feels to observer
Magnitude- Is determined from seismic records that measures the energy release of the earthquake
An Earthquakes intensity and magnitude reflect the size of the seismic waves generated by the earthquake
The depth of the focus determines the magnitude and intensity. Catastrophic earthquakes with high intensity values are almost always shallow-focus events.

11. Richter Scale
Numerical system that measures the energy of the largest seismic waves, called the magnitude, that are produced
Richter magnitude is calculated from the amplitude (height) of the largest seismic wave on the seismogram

12. This scale is a logarithmic scale, which means that each time you go up one unit on the scale, the motion recorded is 10 times greater.
For example, an earthquake with magnitude 5 has 100 times more ground shaking than an earthquake with magnitude of 3.

13. Mercalli Scales
The Richter scale is the most commonly used rating scale that measures the energy released by an earthquake, taking into account the size of the fault rupture, the amount of movement along the fault, and the rocks’ stiffness.
Another way to describe earthquakes is with respect to the amount of damage
The Mercalli scale: uses the observations of people to estimate its intensity.

14. Mercalli Scales
This scale is not as scientific and relies on the reports of people who may over-exaggerate how bad the shaking was during the earthquake.
Also, the amount of damage reported may not accurately record the strength of the earthquake because the amount of damage varies depending on:
the building design
the distance to the epicentre
the type of surface material (rock or dirt) the buildings are on
Mercalli Scale- 1 to 12

15. Earthquakes and Society
Their currently is no reliable way to forecast the exact time and location of the next earthquake, however we do have strategies of earthquake prediction:
The probability of an earthquake’s occurrence is based on two factors:
History of earthquakes in an area
Simic belts, greater probability
Recurrence rate, regular intervals
Rate at which strain builds up in the rocks
Seismic gap

16. Major Hazards of Earthquakes
Earthquakes don’t kill people:
Building Collapse
Landslides
Fire
Tsunamis

17. Tsunamis Travel about 4500-800 Km/h
Pass Unnoticed at Sea, Cause Damage on Shore

18. Can you locate an Earthquake!?