1. Objectives 1. Compare the 3 types of seismic waves.
2. Discuss the method scientists use to pinpoint an Earthquake (EQ).
3. Discuss the method most commonly used to measure the magnitude of EQs.

2. 3 major Types of Seismic Waves
P waves: primary wave.
Move fastest
1st to be recorded
Travels through solids & liquids
More rigid material. = faster

4. 3 major Types of Seismic Waves
S waves: secondary waves.
2nd waves to be recorded
Only travel trough solids

6. 3 major Types of Seismic Waves
L waves: surface waves, also called long waves.
Converted from P & S waves when they reach the surface
Slowest-moving waves
Last to be recorded
Cause surface to rise & fall

7. Comparing Seismic Waves
Primary Waves (P)
Secondary Waves (S)
Long or Surface Waves (L)
Arrives first
Moves faster through more rigid material
Moves the ground together and apart along the direction of waves.
Arrive seconds
About 1.7 times slower than the Primary waves
Moves the ground at right angles to the direction in which the waves are traveling
Arrives last
Slowest of the three
Travels over the earths surface
Moves the ground like the ocean waves
Can cause great damages when traveling through loose earth

8. Recording EQs
Seismograph: instrument used to detect and record seismic waves.
Determines the distance and not the direction of the epicenter.

9. Locating an EQ
Distance-Determined by seismograph-
scientists analyze the difference between the arrival times of the P and the S waves.
Locating the epicenter-At least 3 seismograph is needed to locate the epicenter.
The method is called Triangulation.

10. Two recording N.S and E.W vibrations
One recording vertical vibrations

11. Locating an EQ Scientists compare time diff. btwn P & S waves.
Plot on graph to get distance to epicenter

12. Triangulation
EX: 3 seismographs at locations A, B, and C, determined the distance of each point from the epicenter.
Point A (seismograph 1)is 500 km, point B (seismograph 2) is 800 km and point C is 1200 km ( seismograph 3) away from the epicenter. Locate the epicenter.

13. Locating an EQ Need 3 plots to locate epicenter
Point where all 3 circles meet is location of epicenter

14. EQ Scales Richter Scale Mercalli Scale
Measures the magnitude or the energy released by an earthquake.
Scale of 1 to 10
Each level releases 31.7 times more energy than that of the lower level
Largest registered, 9.5 Richter, Chile 1960.
Strong-7 or above
Moderate 6-7
Minor-2.5-6
Microquakes-2.5 or less. Can not be felt by people
Expresses the intensity or the amount of damage it causes.
Shown by Roman numerals from I to XII.
I-II- Low intensity, little damage
Up to X- Higher intensity, well built structures destroyed.
XII- total destruction

15. EARTHQUAKE DAMAGE
Movement of the ground itself seldom causes many deaths or injuries.
Most injuries result from the collapse of the buildings, flying glass and falling objects.

16. Damages
Flood
Fire
Landslide
Most buildings are not designed to withstand the swaying motion caused by earthquakes.
Buildings may collapse, sway violently, or tip over to the neighboring structure.
Tall buildings should be built on soil or rock that is firm. Loose soil and rock can vibrate like jelly.

18. Tsunami (harbor wave)
Faulting and under water landslides can cause tsunamis. Tsunamis can cause massive death and damages.

19. SSWWS:
Seismic Sea Wave Warning System: Seismic network around the Pacific Ocean. Allows scientist to estimate the arrival times of the tsunamis at different locations.