1. Types of Faults and seismic waves

2. What is a fault?
A fault is a break in the rocks that make up the Earth’s crust, along which rocks on either side have moved past each other.
The direction of movement along the fault plane determines the fault type.

3. GEOLOGICAL CONCEPTS TYPES OF FAULT Footwall/Hanging wall from Mining geology
Miners put their lamps on the hanging wall and
walk on the foot wall.

4. Three major Faults
Normal
Reverse
Strike-slip

5. Normal Fault The hanging wall moves down relative to the foot wall.
This fault type is caused by tensional stress.

6. Normal Fault

7. Normal Fault

8. Normal Fault

9. Reverse Fault The hanging wall moves up relative to the foot wall.
This fault is caused by
Compressional stress.

10. Reverse Fault

11. Reverse Fault

12. Reverse Fault

13. Strike-Slip Fault The fault exists between two pieces of crust and the
Movement occurs
horizontally where
the sides slide past
each other.
This fault type is caused by shear stress.

14. Strike-Slip Fault

15. Strike Slip Fault

16. Strike-Slip Fault

17. Fault Movement = Earthquakes
An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.

18. Focus- where the slip happens below ground
Epicenter-where the shaking is first felt above
ground directly above the focus.

19. Slippage along fault initiates seismic waves in all directions radiating from the focus.
Seismic waves are vibrations that travel through the Earth carrying the energy released during earthquakes

21. Primary Waves
P waves- are the first waves to arrive at a seismograph station.
-Are the fastest form of wave, sometimes called compression waves.
Can move through both liquids and solids.
These waves cause rock particles to move back and forth in the same direction as the wave is traveling.

22. Secondary Waves
S-Waves- arrive after the primary waves at the seismograph station.
-Can travel through solids only.
-Cause particles to move back and forth at right angles to the line of wave movement

23. SEISMOLGY EARTHQUAKE LOCATION Travel time versus distance plots
Can construct distance versus travel time for earthquakes knowing properties of earth’s interior
Note that with increasing distance the arrival times for the various waves separates.
The 3 min 45 sec difference between the arrival time of the P and S waves corresponds to a distance of 2000 km.

24. SEISMOLOGY LOCATING EARTHQUAKES Triangulation
-Need three different seismic stations to locate an earthquake.
-Measure the P-S arrival times and convert these to distance.
-Triangulate using radius given by P-S travel times.
-Triangulation for position of an earthquake near New Madrid using stations in Columbus, St Louis and Memphis

25. Measuring Earthquakes
Magnitude- the amount of energy released during an EQ
Richter Scale- based on the largest seismic waves generated by the EQ on a factor of 10.
Moment Magnitude Scale- considers the size of the fault rupture, the amount of movement, and rock’s stiffness

26. Modified Mercalli Scale
Measures the intensity of the EQ using a rating system of the damage
Scientists compile information from various observers within different zip codes to get a better understanding of the devastation caused by an EQ to determine its intensity.