Earth SciencePhysical GeologyEarth SciencePhysical Geology
EarthquakesEarthquakes
Chapter 6Chapter 6
Notes 2Notes 2
EarthquakesEarthquakes
Focus:Focus:
Spot on fault plane where movement firstoccursSpot on fault plane where movement firstoccurs
Epicenter:Epicenter:
Point on the earth’s surface directly above thefocus; often the spot of most devastationPoint on the earth’s surface directly above thefocus; often the spot of most devastation
Seismic wave radiate outward from thefocus in all directionsSeismic wave radiate outward from thefocus in all directions
EarthquakesEarthquakes
Shallow focus:Shallow focus:
90% of earthquakes90% of earthquakes
Occur within 70 km of the surfaceOccur within 70 km of the surface
Most destructiveMost destructive
Intermediate focus:Intermediate focus:
Occur between 70 and 300 kmOccur between 70 and 300 km
Deep focus:Deep focus:
Occur between 300 and 650 kmOccur between 300 and 650 km
Occur farther inland in a subduction zone thanany other focusOccur farther inland in a subduction zone thanany other focus
Major Earthquake ZonesMajor Earthquake Zones
Most earthquakes occur at plateboundariesMost earthquakes occur at plateboundaries
Three major zones:Three major zones:
Pacific Ring of FirePacific Ring of Fire
Subduction and transform (shearing)Subduction and transform (shearing)
Mid-Ocean RidgesMid-Ocean Ridges
Tension or divergentTension or divergent
Eurasian-Melanesian BeltEurasian-Melanesian Belt
ConvergentConvergent
Recording EarthquakesRecording Earthquakes
Seismograph:Seismograph:
Instrument used to detect and record seismicwavesInstrument used to detect and record seismicwaves
Has three sensing devices:Has three sensing devices:
Vertical movementVertical movement
East-west directionEast-west direction
North-south directionNorth-south direction
Traces wave-shaped lines on paper, acomputer or magnetic tapeTraces wave-shaped lines on paper, acomputer or magnetic tape
Types of Seismic WavesTypes of Seismic Waves
P waves: (primary waves)P waves: (primary waves)
Fastest moving waves; First recorded by aseismographsFastest moving waves; First recorded by aseismographs
Travel through solids and liquidsTravel through solids and liquids
The more rigid the material, the faster thewave movesThe more rigid the material, the faster thewave moves
S wave: (secondary waves – shear waves)S wave: (secondary waves – shear waves)
Slower than P waves; Second to be recordedSlower than P waves; Second to be recorded
Can only travel through solidsCan only travel through solids
Rock particles move in right anglesRock particles move in right angles
Types of Seismic WavesTypes of Seismic Waves
L wave: (surface waves)L wave: (surface waves)
Slowest moving wavesSlowest moving waves
Only travel on the surface of the earth, notthrough the interiorOnly travel on the surface of the earth, notthrough the interior
Cause the surface to rise and fall like anocean waveCause the surface to rise and fall like anocean wave
Cause the most destruction during anearthquakeCause the most destruction during anearthquake
Locating an E-quakeLocating an E-quake
P waves travel 1.7 time faster than S wavesP waves travel 1.7 time faster than S waves
If a scientist knows what time the P waves andS waves arrive at a seismograph station, theycan determine how far away the epicenter isfrom that same location.If a scientist knows what time the P waves andS waves arrive at a seismograph station, theycan determine how far away the epicenter isfrom that same location.
If P waves and S waves arrive close to the same time,the epicenter is near by.If P waves and S waves arrive close to the same time,the epicenter is near by.
Time Travel GraphTime Travel Graph
Earthquake MeasurementEarthquake Measurement
Magnitude: measure of the energyreleased by an earthquake and thedescription of ground motionMagnitude: measure of the energyreleased by an earthquake and thedescription of ground motion
Richter Scale: relates magnitude to thedamage; used mostly by reports and non-scientistsRichter Scale: relates magnitude to thedamage; used mostly by reports and non-scientists
TsunamisTsunamis
Giant wave created by an earthquake onthe ocean floorGiant wave created by an earthquake onthe ocean floor
Caused by faulting or underwaterlandslidesCaused by faulting or underwaterlandslides
Both causes a sudden drop in ocean floor anddisplaces a large amount of waterBoth causes a sudden drop in ocean floor anddisplaces a large amount of water
Creates long, low wavesCreates long, low waves
TsunamisTsunamis
Pacific Tsunamis Warning Center (PTWC)Pacific Tsunamis Warning Center (PTWC)
Network of seismograph stations around andthe Pacific OceanNetwork of seismograph stations around andthe Pacific Ocean
Issues warnings to areas deemed to be indangerIssues warnings to areas deemed to be indanger
Not found in the area where the last tsunamisoccurredNot found in the area where the last tsunamisoccurred
Even if there were stations located there, no wayto warn people…no mediaEven if there were stations located there, no wayto warn people…no media