Earthquakes

1. Earthquakes

2. Rocks move along faults. • Fault: A fracture, or break, in the Earth’s lithosphere, where blocks of rock move past each other.

3. The rocks bend as stress is put on them. • Stress: the force exerted when an object presses on, pulls on, or pushes against another object.

4. A sudden release of stress in the lithosphere causes an earthquake. • Earthquake: The shaking of the ground caused by the sudden movement of large blocks of rock along a fault.

5. The strength of an earthquake depends on: • How much stress builds up before the rocks move • The distance the rocks move along the fault

6. Faults are classified by how rocks move. • The three main types of faults are: • Normal faults • Reverse faults • Strike-slip faults

7. Normal Faults • The block of rock above the fault plane slides down relative to the other block. • Stress that pulls rocks apart causes normal faults. • Common in the Great Rift Valley of Africa.

8. Reverse Faults • The block of rock above the fault plane moves up relative to the other block. • Stress that presses rocks together causes reverse faults. • Common in the Himalaya Mountains.

9. Strike-Slip Faults • Blocks of rock move sideways or horizontally on either side of the fault plane. • Stresses that push blocks of rock horizontally cause earthquakes along strike-slip faults. • The San Andreas Fault is a strike-slip fault.

10. Liquefaction • Liquefaction: shaking causes water saturated sediments to lose strength and act as if it were a liquid • 3 factors are required for liquefaction to occur: • 1. loose sand and silt grains • 2. water filling the space between the grains • 3. strong shaking

11. Energy from earthquakes travels through Earth. • The energy travels as seismic waves. • Seismic waves: vibrations caused by earthquakes.

12. All earthquakes start beneath Earth’s surface. • Focus of an earthquake: the point underground where rocks first begin to move • Epicenter: the point on Earth’s surface directly above the focus • If two earthquakes of equal strength have the same epicenter, the one with the shallower focus causes more damage.

13. Earthquakes produce three types of seismic waves: • Primary waves • Secondary waves • Surface waves

14. Primary Waves or P waves • Fastest seismic waves • These waves are the first to reach any particular location after an earthquake occurs. • Can travel through solids, liquids, and gases. • As these waves pass through a material, the particles of the material are slightly pushed together and pulled apart.

15. Secondary Waves or S waves • These are the second seismic waves to arrive at any particular location after an earthquake. • Secondary waves travel through Earth’s interior at about half the speed of primary waves. • Only travel through solids. • As these waves pass through a material, the particles of the material are shaken up and down and side to side.

16. Surface Waves • Seismic waves that move along Earth‘s surface, not through its interior. • These waves make the ground roll up and down in a rolling motion. • Surface waves cause the largest ground movement and the most damage. • Surface waves move the slowest.

17. Seismic waves can be measured. • Seismic stations are places where ground movements are measured. • Seismometer: an instrument that constantly records ground movement • Seismogram: the recording produced by a seismograph

18. Earthquake magnitude scales describe the huge range in energy. • Magnitude is the measure of an earthquake’s relative size • Richter scale: this scale is based on how fast the ground moves at a seismic station • Moment magnitude scale: this scale is based on the total amounts of energy released by earthquakes