Post on 24-Dec-2015
transcript
Earthquake Study
• Seismology – the study of earthquakes (#27)
• Seismologist – person who studies earthquakes
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
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
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)
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
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
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
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 Effects
• Ground shaking
• Liquefaction – solid earth turns to liquid
• Surface faulting
• Landslides
• Fires
• Tsunami
Earthquake Effects - Landslides
Turnagain Heights, Alaska,1964 (upper left inset);Santa Cruz Mtns, California , 1989
Source: National Geophysical Data Center