Earthquakes
What is an earthquake?
•Earthquake: a sudden release of energy in earth’scrust that causes movement
Why Earthquakes happen
•Friction prevents movement along a fault
•Fault: a fracture in a rock formation wheremovements occurs
•Sudden release causes a quake
Elastic Rebound
•Elastic rebound: the sudden return of deformedrock to its original position
•Fence offset 8 1/2 feet bymain fault in ruralCalifornia1906.
Anatomy of an Earthquake
•Focus: the location within Earth along a fault atwhich the first motion of an Earthquake occurs
•The shallower the focus, the more destructive thequake
Anatomy of an Earthquake
•Epicenter: the location on Earth’s surface directlyabove the focus
Seismic Waves
•Seismic Waves: Vibrations caused byearthquakes
Body Waves
•Body waves: seismic waves that travel throughearth’s interior
•Two types:
•Primary waves: P-waves- Fastest and the firstto be detected
•Can move through solids, liquids, or gas
Body Waves continued
•Secondary waves: S-waves- shake theground back and forth (2nd fastest)
•Can move through solids ONLY
Surface waves
•Surface waves: Only movealong the surface of Earth
•Slower, but cause the mostdamage
Surface Waves
•Love waves: fastest surface waves
•Move rock side to side
Diagram of love wave
Surface Waves
Rayleigh waves: also called a “ground roll”
Moves rock in a circular motion
Seismic Waves and Earth’sInterior
•The composition of the material a seismic wavemoves through affect their speed and direction
•Andrija Mohorovicic (1909): used seismic waves tofind the depth of the mantle
![[Andrija Mohorovičić]](http://www.seismosoc.org/publications/SRL/SRL_78/images/A_Mohorovicic1.jpg)
Seismic Waves and Earth’sInterior
•Shadow Zones: locations on Earth’s surfacewhere no body waves from a particularearthquake can be detected
Seismic Waves and Earth’sInterior
•P-waves are bent as theypass through different layers
•S-waves are blocked by theliquid outer core becausethey can only travel throughsolids
•Activity 1: Seismic Waves
•Reflection and extension quiz
Studying Earthquakes
•Seismograph: an instrument that detects andrecords seismic waves
•Seismogram: the recorded tracing produced bya seismograph
Studying Earthquakes (cont.)
•Different waves move at different speeds:
•P-waves arrive first, then S-waves, then Surfacewaves
Locating an Earthquake
•The longer the lag time between P-waves and S-waves,the further away the earthquake is
•The location of an earthquake can be found bytriangulation: using the distance from 3 stations to findthe epicenter of the earthquake
Measuring Earthquakes
•Magnitude: the strength of a quake
Measuring Earthquakes
•Richter Scale: assigns a number to define theenergy released during an earthquake
Measuring Earthquakes
•Big numbers = strongerearthquakes
Taiwan (1999)
Measuring Earthquakes
•Intensity: the amount of damage caused by an earthquake
Tsunamis
•Tsunami: a giant wave caused by an earthquakeon the ocean floor
Earthquake Safety
Earthquake Safety
•Earthquakes are more likely to happen in some places,but can happen anywhere
•Before: have supplies on hand
•Such as: food, water, flash lights, batteries, radios and a firstaid kit
•During: stand in a doorway, stay away from windowsand tall things
•Protect your head from falling objects
•Drop, Cover and Hold On
•After: be cautious of fires, downed powerlines, etc.
•Remove yourselves from buildings and check for structural damage.
EarthquakeWarnings/Forecasts
•Scientists study past quakes to predict where futurequakes are most likely to occur
•There is No reliable way to predict when or wherean earthquake will happen
•When stress is building up in rock, sensors candetect tilting and cracking
•Foreshocks usually happen before a largeearthquake