Earthquakes

Plate Boundaries

Sketch the 3 type of plate boundaries

Pacific-North American Plate Boundary

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

DivergentReverse

Convergent

Strike-slip

Transform

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 earthquakeDecember 16, 1954

Thrust Fault Example

Thrust Fault Example

Strike-slip Fault Example

Strike-slip Fault Example

1906 San Francisco Earthquake

Earthquake Effects

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

Earthquake Effects - Ground Shaking

KGO-TV News ABC-7

Loma Prieta, CA 1989

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

Turnagain Heights, Alaska,1964 (upper left inset);Santa Cruz Mtns, California , 1989

Source: National Geophysical Data Center

Earthquake Effects - Fires

KGO-TV News ABC-7

Loma Prieta, CA 1989

Earthquake Effects - Tsunamis

Photograph Credit: Henry Helbush. Source: National Geophysical Data Center

1957 Aleutian Tsunami