1. Earthquakes

2. What is an Earthquake?
Earthquake--Occur when rocks under stress shift along a fault (energy released)
Fault—break in rock where one block moves relative to another

3. Let’s Build a Fault Model!

4. Damage from Northridge Earthquake in Southern California--1994

7. Anatomy of an Earthquake
Focus--1st motion of earthquake in Earth, along fault
Epicenter—point on Earth’s surface directly above focus
90% of continental earthquakes have shallow focus—most damaging

8. Parts of an Earthquake

9. Elastic Rebound
Elastic Rebound —sudden return of deformed rock to undeformed shape
Elastic rebound causes earthquakes

10. Fence offset due
to Elastic Rebound

11. Seismic Waves
When rocks on a fault move, they release energy as seismic waves
Seismic waves travel outward from the focus in all directions

12. Body wave—seismic wave that travels thru a medium
two types: P-wave & S-wave

13. Seismic Waves
P (primary) waves are the fastest & travel thru solids, liquids, & gases

14. Seismic Waves
S (secondary) waves are 2nd fastest & travel thru solids only. Although slower they can cause the most damage

15. Seismic Waves
Surface wave— a seismic wave that travels along surface of medium. These are S & P waves that reach the surface & can cause greatest damage

16. Water Wave and Slinky Activities!

17. WAYS TO MEASURE AN EARTHQUAKE
There are two major scales to measure an earthquake:
Mercalli Scale: measures earthquake intensity (by amount of damage caused)
Richter Scale: measures earthquake magnitude (strength)

19. Studying Earthquakes Seismology— study of earthquakes & seismic waves
Seismograph— records vibrations in ground
Seismogram— tracing of EQ motion, recorded by seismograph

20. Bill Nye on the Richter Scale http://www. youtube. com/watch
Bill Nye on the Richter Scale Bill Nye on Waves Earthquake recording station/seismograph clip

21. SEISMOGRAM Order of recording: P-waves, S- waves, then surface waves
Shows S-P lag time

22. P-Wave
S-Wave
S-Wave
P-Wave
S-Wave
P-Wave
To find S-P lag time, subtract where the P wave starts from where the S wave starts (S-P = Lag Time)

23. What is S-P lag time for San Francisco, CA?
What is S-P lag time for El Paso,TX?
28 sec – 0 sec = 28 sec lag time
What is S-P lag time for San Francisco, CA?
120 sec – 0 sec = 120 sec lag time
What is S-P lag time for Seattle, WA?
165 sec – 0 sec = 165 sec lag time
Which city is closest to the epicenter?
The city with the shortest lag time is closest to the epicenter, so it’s El Paso, TX

24. Locating Earthquakes Through Triangulation
S-P lag times are analyzed to find the epicenter of Earthquakes using 3 stations
Why 3 stations?
Because all we know is distance, so it takes 3 circles to narrow it down to one point
Epicenter

25. Let’s stop here and practice finding S P lag time

26. Fault Zones
Fault zone —region w/ lots of faults that typically form at plate boundaries
Fault zones and earthquakes can occur away from plate boundaries as well

27. Fault Zones—New Madrid
New Madrid fault line—New Madrid, MO—120 miles southward on I-55
1811/1812—most widely felt series of E.Q. in U.S. history (2000+)
Five were 8.0+
Ancient fault zone deep in crust of Mississippi River region

29. Tsunamis
Tsunami—giant ocean wave that forms after volcanic eruption, submarine earthquake or landslide
May form when ocean floor rises due to earthquake
Tsunami animation

30. Japan’s Tsunami Before and After…(Google Earth)