Earthquakes

Plate Boundaries Sketch the 3 type of plate boundaries

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

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

Where? Most occur near tectonic plate boundaries

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

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

Normal Divergent Strike-slip Transform Reverse Convergent

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

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

Draw pictures of P and S Waves

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)

Earthquake Location

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

Finding Epicenter – Step 2

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

Richter Magnitude Scale

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

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

Earthquake Forecasting

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

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

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

Earthquake Examples Normal Reverse Strike slip

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

Thrust Fault Example

Thrust Fault Example

Strike-slip Fault Example Strike-slip example moletrack

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

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

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

Earthquake Effects - Ground Shaking Kobe, Japan 1995

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

Earthquake Effects - Surface Faulting Landers, CA 1992

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

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

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