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Presentation on theme: "Earthquakes."— Presentation transcript:

1 Earthquakes

2 Plate Boundaries Sketch the 3 type of plate boundaries

3 Pacific-North American Plate Boundary
LA on Pacific Plate San Francisco on North American Plate San Andreas Fault is boundary Relative motion Takes Big Bend above LA area and causes compression in our area

4 Earthquake Study Seismology – the study of earthquakes (#27)
Seismologist – person who studies earthquakes

5 Where? Most occur near tectonic plate boundaries

6 Causes Deformation – bending, tilting, and breaking of Earth’s crust (#28) Caused by plates pushing, pulling & sliding 2 kinds of deformation Plastic – bends like piece of soft clay No earthquake Elastic – stretches like a rubber band Earthquake

7 Elastic Rebound Elastic rebound – sudden return of elastically deformed rock to its undeformed shape Like a stretched rubber band that breaks and returns to its unstretched shape, now in 2 pieces Energy released as seismic waves

8 Normal Divergent Strike-slip Transform Reverse Convergent

9 Body Waves Seismic waves – waves of energy that travel through Earth, away from an earthquake in all directions (#29) Two types of body waves that travel through interior of Earth P waves Primary waves (#30) Pressure waves (#30) Back and forth motion (#30) Go through solid, liquid, gas Fastest wave S waves Secondary waves (#31) Shear waves (#31) Side to side motion (#31) Go through solids only Slower wave, 2nd to arrive

10 More Waves Surface waves – waves that move in top few km of the crust
Up, down, circular motion Back and forth motion Travel slower than body waves More destructive

11 Draw pictures of P and S Waves

12 Measurement Seismograph – instrument that records ground vibrations to find location and strength of earthquake Seismogram – tracing of earthquake motion created by a seismograph Epicenter – point on Earth’s surface directly above an earthquake (#32) Focus – point on a fault where earthquake motion first occurs (#33)

13 Earthquake Location

14 Finding Epicenter – Step 1
Scientists use the S-P Time Method Use a time-distance graph S and P curves are already calculated Determine distance away from epicenter for at least 3 seismograms

15 Finding Epicenter – Step 2

16 Earthquake Strength Richter Magnitude Scale –
Created in 1930s by Charles Richter Magnitude measures strength of earthquake by ground motion adjusted for distance from epicenter Each unit represents 10x increase in strength 5.0 is 10x stronger than a 4.0 6.0 is 100x stronger than a 4.0

17 Richter Magnitude Scale

18 Earthquake Intensity Intensity – degree to which earthquake is felt and amount of damage caused Modified Mercalli Intensity Scale Numerical scale from I to XII I not felt by people XII total destruction Intensity values highest near epicenter

19 Earthquake Hazards How likely area is to have a damaging quake in the future

20 Earthquake Forecasting

21 Gap Hypothesis Areas on active faults that haven’t had many earthquakes are likely to be sites for future strong earthquakes. Known as seismic gaps

22 Earthquake Preparations
Resistant buildings Mass damper Active tendon system Base isolators Cross braces Flexible pipes Retrofitting Reinforce columns Fasten to foundation

23 What to do in an Earthquake
Before shaking Put heavy objects down low Have an emergency meeting place Store emergency supplies During shaking Crouch or lie under a strong table or desk Outside – lay down away from buildings, trees, power lines Stop car and stay inside After shaking Stay calm and think Get away from danger areas Prepare for aftershocks Follow emergency plan

24 Earthquake Examples Normal Reverse Strike slip

25 Normal Fault Example Dixie Valley-Fairview Peaks, Nevada earthquake
December 16, 1954

26 Thrust Fault Example

27 Thrust Fault Example

28 Strike-slip Fault Example
Strike-slip example moletrack

29 Strike-slip Fault Example
Before earthquake manure pile was under window where farmer shoveled it out from inside Fault runs right under corner of barn After earthquake manure pile moved over about 10 feet 1906 San Francisco Earthquake

30 Earthquake Effects Ground shaking
Liquefaction – solid earth turns to liquid Surface faulting Landslides Fires Tsunami

31 Earthquake Effects - Ground Shaking
Loma Prieta, CA 1989 KGO-TV News ABC-7

32 Earthquake Effects - Ground Shaking
Kobe, Japan 1995

33 Earthquake Effects - Liquefaction
Source: National Geophysical Data Center Niigata, Japan 1964

34 Earthquake Effects - Surface Faulting
Landers, CA 1992

35 Earthquake Effects - Landslides
Source: National Geophysical Data Center Turnagain Heights, Alaska,1964 (upper left inset); Santa Cruz Mtns, California , 1989

36 Earthquake Effects - Fires
Loma Prieta, CA 1989 KGO-TV News ABC-7

37 Earthquake Effects - Tsunamis
1957 Aleutian Tsunami Photograph Credit: Henry Helbush. Source: National Geophysical Data Center

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