Earthquakes
HOW AND WHEREEARTHQUAKES HAPPENHOW AND WHEREEARTHQUAKES HAPPEN
Why Earthquakes Happen?Why Earthquakes Happen?
Rocks along faults pressed tightly together.Rocks along faults pressed tightly together.
Stress occurs but friction prevents them frommoving – fault is said to be locked.Stress occurs but friction prevents them frommoving – fault is said to be locked.
Rocks under stress suddenly shift along a faultRocks under stress suddenly shift along a fault
Fault – break in body of rock where one blockslides relative to anotherFault – break in body of rock where one blockslides relative to another
When rocks along a fault move, a suddenrelease of energy occurs causing movementson the ground...When rocks along a fault move, a suddenrelease of energy occurs causing movementson the ground...
….This is an….This is an
EarthquakeEarthquake
![[A picture of earthquake-moved railroad tracks]](http://cse.ssl.berkeley.edu/img/earthquakes/Railroad.gif)
FOCUSFOCUS
Area along a fault where the slippage firstoccursArea along a fault where the slippage firstoccurs
Focus is beneath the earth’s surfaceFocus is beneath the earth’s surface
The epicenter is directly aboveThe epicenter is directly above
The depth of the focus varies – 90% ofcontinental earthquakes have shallow focusThe depth of the focus varies – 90% ofcontinental earthquakes have shallow focus
Shallow foci – within 70km from surfaceShallow foci – within 70km from surface
Deep foci – subduction zones farther fromplate boundaries than shallow quakesDeep foci – subduction zones farther fromplate boundaries than shallow quakes
FOCUS DEPTH - 1975-95FOCUS DEPTH - 1975-95
FOCUS DEPTH OFEARTHQUAKES INWASHINGTON 1977-1996FOCUS DEPTH OFEARTHQUAKES INWASHINGTON 1977-1996
EPICENTEREPICENTER
A point on the earth’s surface directlyabove the focusA point on the earth’s surface directlyabove the focus
What happens when rocks inmotion release energy in theform of vibrations?
Seismic WavesSeismic Waves
travel outward in all directions from focustravel outward in all directions from focus
Seismic WavesSeismic Waves
Two types of waves produced fromearthquakes :Two types of waves produced fromearthquakes :
Body waves – travel through body ofa mediumBody waves – travel through body ofa medium
Surface waves – travel along surfaceof body rather than through middleSurface waves – travel along surfaceof body rather than through middle
Surface WavesSurface Waves
Form from motion along shallow fault or byenergy transfer from P and S wavesreaching earth’s surface.Form from motion along shallow fault or byenergy transfer from P and S wavesreaching earth’s surface.
Slowest moving seismic wavesSlowest moving seismic waves
Cause greatest damage at surfaceCause greatest damage at surface
Two types : Love and RayleighTwo types : Love and Rayleigh
Love and Rayleigh WavesLove and Rayleigh Waves
Love waves – rockmoves side-to-sideand perpendicularto wave directionLove waves – rockmoves side-to-sideand perpendicularto wave direction
Rayleigh waves –move ground in anelliptical rollingmotionRayleigh waves –move ground in anelliptical rollingmotion
Earthquakes and Plate TectonicsEarthquakes and Plate Tectonics
Most earthquakes are located at or neartectonic plate boundariesMost earthquakes are located at or neartectonic plate boundaries
Convergent Oceanic EnvironmentsConvergent Oceanic Environments
Plates move toward one another and collidePlates move toward one another and collide
Subduction occurs as denser plate sinks underoverriding plate - earthquakes occurSubduction occurs as denser plate sinks underoverriding plate - earthquakes occur
Oceanic-oceanic or oceanic-continentalOceanic-oceanic or oceanic-continental
Divergent Oceanic EnvironmentsDivergent Oceanic Environments
Plates moving away from each other andmid-ocean ridgePlates moving away from each other andmid-ocean ridge
Spreading motion causes earthquakesSpreading motion causes earthquakes
Continental EnvironmentsContinental Environments
Two continental plates converge, diverge,or move horizontally to one anotherTwo continental plates converge, diverge,or move horizontally to one another
Rocks build up stressRocks build up stress
Mountains form and earthquakes occurMountains form and earthquakes occur
MAJOR EARTHQUAKE ZONESMAJOR EARTHQUAKE ZONES
Pacific Ring of FirePacific Ring of Fire
Mid-ocean ridgesMid-ocean ridges
Eurasian-Melanesian Mountain BeltEurasian-Melanesian Mountain Belt
MAJOR EARTHQUAKESAREASMAJOR EARTHQUAKESAREAS
Fault ZonesFault Zones
Intense stress along plate boundaries createfault zonesIntense stress along plate boundaries createfault zones
Plates separate, collide, subduct or slide pastone anotherPlates separate, collide, subduct or slide pastone another
Movement from stress buildup causes majorearthquakesMovement from stress buildup causes majorearthquakes
PUGET SOUND FAULTZONESPUGET SOUND FAULTZONES
Studying EarthquakesStudying Earthquakes
Ancient Chinese Method of Studying Earthquakes
MagnitudeMagnitude
The measure of thestrength of anearthquake,determined bymeasuring theamount of groundmotion.The measure of thestrength of anearthquake,determined bymeasuring theamount of groundmotion.
Richter ScaleRichter Scale
Used for most of the20th century. Eachnumber represents afactor of 30 (a 5earthquake has 30times the energy of a4). We now prefer touse the……Used for most of the20th century. Eachnumber represents afactor of 30 (a 5earthquake has 30times the energy of a4). We now prefer touse the……
Moment MagnitudeMoment Magnitude
Based on the size of the area of fault movement, theaverage distance that the fault blocks move, and therigidity of the rocks in the fault zone. More accuratefor large earthquakes.Based on the size of the area of fault movement, theaverage distance that the fault blocks move, and therigidity of the rocks in the fault zone. More accuratefor large earthquakes.
IntensityIntensity
Based on an earthquake’seffects. The Mercalliscale (p. 304) uses Romannumerals I-XII. Dependson magnitude, distancefrom the epicenter, localgeology, earthquakeduration, and humaninfrastructure.Based on an earthquake’seffects. The Mercalliscale (p. 304) uses Romannumerals I-XII. Dependson magnitude, distancefrom the epicenter, localgeology, earthquakeduration, and humaninfrastructure.
Charleston, SC - 1886
I & III & II
Not felt except by avery few.Not felt except by avery few.
Felt by a few personson the upper floorsof buildings.Felt by a few personson the upper floorsof buildings.
III & IVIII & IV
Felt indoors.Felt indoors.
Hanging objectsswing.Hanging objectsswing.
V & VIV & VI
Felt outdoors.Felt outdoors.
Felt by all, manyscared and runoutdoors.Felt by all, manyscared and runoutdoors.
VII & VIIIVII & VIII
Difficult to stand.Difficult to stand.
Damage slight inspecially designedstructures.Damage slight inspecially designedstructures.
IX & XIX & X
Damage considerable inspecially designedstructures.Damage considerable inspecially designedstructures.
Ground cracked, railsbent.Ground cracked, railsbent.
XI & XIIXI & XII
Bridges destroyed,broad fissures inground.Bridges destroyed,broad fissures inground.
Total destruction.Total destruction.
Earthquakes and SocietyEffects on Humans, Property & InfrastructureHow to PREPARE for an EarthquakeEarthquakes and SocietyEffects on Humans, Property & InfrastructureHow to PREPARE for an Earthquake
MAJOR TSUNAMISMAJOR TSUNAMIS
Caused by an earthquake whoseepicenter is on or below the oceanfloor that causing:
A rapid drop or rise in the oceanfloor
OR
An underwater landslide thatdisplaces a large volume of water
Much Safer To Be Out In The OpenMuch Safer To Be Out In The Open
Most injuries resultfrom the collapseof buildings, fallingobjects, and flyingglass.Most injuries resultfrom the collapseof buildings, fallingobjects, and flyingglass.
Other Dangers IncludeOther Dangers Include
LandslidesLandslides
FiresFires
Explosions (broken electric and gas lines)Explosions (broken electric and gas lines)
Floods (from collapsing dams)Floods (from collapsing dams)
Ground Type Is ImportantGround Type Is Important
Loose soil and rockcan vibrate likeJell-O.Loose soil and rockcan vibrate likeJell-O.
KOBE SEISMOGRAPHTop - Station on solid groundRight - Station on watersaturated, soft ground KOBE SEISMOGRAPHTop - Station on solid groundRight - Station on watersaturated, soft ground
LIQUEFACTIONKobeLIQUEFACTIONKobe
Quake DurationQuake Duration
A long duration moderate earthquake cancause more damage than a short one at ahigher magnitude.A long duration moderate earthquake cancause more damage than a short one at ahigher magnitude.
FIRESKobeFIRESKobe
Destruction to Buildings andPropertyDestruction to Buildings andProperty
STRUCTURAL DAMAGEKobe earthquakeSTRUCTURAL DAMAGEKobe earthquake
CHILE – 1960Largest Recorded 9.5CHILE – 1960Largest Recorded 9.5
ALASKA- 19649.2ALASKA- 19649.2
EARTHQUAKE SAFETYPeople who live near active faults should beready to follow a few simple earthquakesafety rules to help prevent death, injury,and property damage
§BEFORE - Be prepared§BEFORE - Be prepared
§DURING - Stay calm§DURING - Stay calm
§AFTER - Stay cautious§AFTER - Stay cautious
Before an EarthquakeBefore an Earthquake
Be prepared. Keep an adequate supplyof food, water, batteries, flashlights anda radio.Be prepared. Keep an adequate supplyof food, water, batteries, flashlights anda radio.
Prepare an earthquake plan anddiscuss it with your family.Prepare an earthquake plan anddiscuss it with your family.
Learn how to turn off the gas, water,and electricity in your home.Learn how to turn off the gas, water,and electricity in your home.
During an EarthquakeDuring an Earthquake
Protect yourself by moving to a safeposition.Protect yourself by moving to a safeposition.
Best way is the “Triangle of Life” (next slide--)Best way is the “Triangle of Life” (next slide--)
Indoors – get under a table or if notpossible in a inside door frame awayfrom heavy furnitureIndoors – get under a table or if notpossible in a inside door frame awayfrom heavy furniture
Outdoors – get away from tallbuildings, tunnels, power lines orbridges out in the openOutdoors – get away from tallbuildings, tunnels, power lines orbridges out in the open
Triangle of Life during a QuakeTriangle of Life during a Quake
Newest research shows your first best positionto get into during a quake is next to and belowthe level of a heavy object – table or furnitureNewest research shows your first best positionto get into during a quake is next to and belowthe level of a heavy object – table or furniture
Cover your head in bracing position (like shown on a plane)Cover your head in bracing position (like shown on a plane)
Any falling debris will hit table or furniture andarc over you and you will be protectedAny falling debris will hit table or furniture andarc over you and you will be protected
Bracing Under a TableEspecially at SchoolBracing Under a TableEspecially at School
Earthquake Warnings andForecasts
Scientists study past earthquakes topredict where future earthquakes willoccur.Scientists study past earthquakes topredict where future earthquakes willoccur.
There is currently no way to predictexactly when an earthquake will occur.There is currently no way to predictexactly when an earthquake will occur.
Seismic Gaps – Areas along a fault wherestress has built up due to a decrease inseismic activity recently but where strongearthquakes occurred in the pastSeismic Gaps – Areas along a fault wherestress has built up due to a decrease inseismic activity recently but where strongearthquakes occurred in the past
Don’t be Scared, Be Prepared!Don’t be Scared, Be Prepared!
3 Days, 3 Ways3 Days, 3 Ways
Earthquake PreparednessStarts NOW!Earthquake PreparednessStarts NOW!
3days3ways.org3days3ways.org
Mr. K will show you how starting Tuesday!Mr. K will show you how starting Tuesday!