Earthquakes!

1. Earthquakes!

3. Earth is never still! • Every year there are 500,000 detectable earthquakes • 100,000 of them can be felt • Only 100 cause damage http://earthquake.usgs.gov/eqcenter/recenteqsww/

4. Ohio Earthquake Facts • Last earthquake occurred January 26, 2008 • Magnitude 1.8 • Largest quake occurred March 9, 1937 • Magnitude 5.4

5. Causes of Earthquakes • All rocks have an elastic limit. • If the forces acting on these rocks exceed this limit or overcome friction between blocks, the crust snaps and an earthquake occurs. • This phenomenon is known as the elastic rebound theory.

6. Causes of Earthquakes • The most common cause of earthquakes is faulting.

7. Causes of Earthquakes • As rocks slide past one another large amounts of energy that has been built up over time is finally released, causing an earthquake. • The point inside the Earth where rock first breaks or moves in called the focus of the earthquake.

8. Classifying Earthquakes • Shallow focus earthquakes originate between the Earth’s surface at a depth of 70 km. • Intermediate focus earthquakes originate between 70-300 km. • Deep focus earthquakes originate between 300-700 km.

9. Classifying Earthquakes

10. Seismic Waves • When an earthquake occurs, energy moves away from the focus in the forms of waves called seismic waves.

11. Seismic Waves • Primary (P) waves are the fastest seismic waves. • They compress and expand like a slinky. • P waves can travel through solid and liquid rock.

12. Seismic Waves • Secondary (S) waves are the second fastest seismic wave. • They vibrate up and down and side to side. • S waves can only travel through solid rock.

13. Seismic Waves • Surface (L) waves are the slowest seismic waves. • L waves travel in a rolling motion along the surface of the Earth.

14. Studying Earthquakes • Scientists use sensitive instruments called seismographs to measure and record seismic waves. • The seismograph’s record of waves is called a seismogram. • A scientist who studies earthquakes is called a seismologist.

15. Studying Earthquakes

16. Studying Earthquakes • The epicenter is the place on the surface of the Earth directly above the focus of the earthquake.

17. Studying Earthquakes • Lag time is the difference between the arrival of the P and S waves.

18. Studying Earthquakes • Seismologists need to take readings form 3 stations in order to locate the epicenter of an earthquake.

19. Studying Earthquakes 1000 km 500 km epicenter 400 km

20. Studying Earthquakes • The magnitude of an earthquake is the total amount of energy released.

21. Studying Earthquakes • The Richter scale is a logarithmic scale used to determine the strength of an earthquake (1-10) based on the energy that is released. • Humans cannot feel any earthquake activity lower than a 3. • Those that measure 6 or more are considered major earthquakes. • The strongest earthquake recorded occurred in Chile in 1960 and had a magnitude 9.5.

22. Studying Earthquakes

23. Studying Earthquakes • The Mercalli scale is a method of describing describing the strength of an earthquake in terms of damage that is done to surrounding structures. • The measure of damage done by an earthquake is called intensity.

24. Earthquake Damage • The effect of an earthquake in a given region depends greatly on the local surface and underground geologic conditions. 1985 Mexico Cityearthquake

25. Earthquake Damage • Loss of human life during earthquakes is usually attributed to falling buildings and fires. 1994 Northridgeearthquake

26. Earthquake Damage 1906 San Franciscoearthquake

27. Earthquake Damage 1994 Northridge earthquake

28. Earthquake Damage • Earthquakes also occur on the floor of the ocean, which often produce displacement of water called tsunami. • Tsunami can travel at speeds up to 700-800 km per hour and can reach heights of up to 20 meters - that is the height of a 6 story building!

29. Earthquake Damage

30. Earthquake Damage 2004 Indonesian tsunami

31. Earthquake Damage 2004 Indonesian Tsunami