EarthquakesHOW AND WHERE HOW AND WHERE

EARTHQUAKES HAPPENEARTHQUAKES 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 from Stress occurs but friction prevents them from

moving – fault is said to be moving – fault is said to be locked.locked.Rocks under stress suddenly shift along a faultRocks under stress suddenly shift along a faultFaultFault – break in body of rock where one block – break in body of rock where one block

slides relative to anotherslides relative to anotherWhen rocks along a fault move, a sudden When rocks along a fault move, a sudden

release of energy occurs causing movements release of energy occurs causing movements on the ground...on the ground...

…….This is an.This is an

EarthquakeEarthquake

FOCUSFOCUSArea along a fault where the slippage first Area along a fault where the slippage first

occursoccurs

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% of The depth of the focus varies – 90% of continental earthquakes have shallow focuscontinental earthquakes have shallow focus

Shallow foci – within 70km from surfaceShallow foci – within 70km from surface

Deep foci – subduction zones farther from Deep foci – subduction zones farther from plate boundaries than shallow quakesplate boundaries than shallow quakes

FOCUS DEPTH - 1975-95FOCUS DEPTH - 1975-95

FOCUS DEPTH OF FOCUS DEPTH OF EARTHQUAKES IN EARTHQUAKES IN

WASHINGTON 1977-1996WASHINGTON 1977-1996

EPICENTEREPICENTER

A point on the earth’s surface directly A point on the earth’s surface directly above the focusabove the focus

What happens when rocks in motion release energy in the

form of vibrations?

Seismic WavesSeismic Wavestravel outward in all directions from focustravel outward in all directions from focus

Seismic WavesSeismic Waves

Two types of waves produced from Two types of waves produced from earthquakes :earthquakes :

Body waves – travel through body of Body waves – travel through body of a mediuma medium

Surface waves – travel along surface Surface waves – travel along surface of body rather than through middleof body rather than through middle

Surface WavesSurface Waves

Form from motion along shallow fault or by Form from motion along shallow fault or by energy transfer from P and S waves energy transfer from P and S waves reaching earth’s surface.reaching earth’s surface.

Slowest moving seismic wavesSlowest moving seismic wavesCause greatest damage at surfaceCause greatest damage at surfaceTwo types : Love and RayleighTwo types : Love and Rayleigh

Love and Rayleigh WavesLove and Rayleigh WavesLove waves – rock Love waves – rock

moves side-to-side moves side-to-side and perpendicular and perpendicular to wave directionto wave direction

Rayleigh waves – Rayleigh waves – move ground in an move ground in an elliptical rolling elliptical rolling motionmotion

Earthquakes and Plate TectonicsEarthquakes and Plate Tectonics

Most earthquakes are located at or near Most earthquakes are located at or near tectonic plate boundariestectonic plate boundaries

Convergent Oceanic EnvironmentsConvergent Oceanic EnvironmentsPlates move toward one another and collidePlates move toward one another and collideSubduction occurs as denser plate sinks under Subduction occurs as denser plate sinks under

overriding plate - earthquakes occuroverriding plate - earthquakes occurOceanic-oceanic or oceanic-continentalOceanic-oceanic or oceanic-continental

Divergent Oceanic EnvironmentsDivergent Oceanic Environments

Plates moving away from each other and Plates moving away from each other and mid-ocean ridgemid-ocean ridge

Spreading motion causes earthquakesSpreading motion causes earthquakes

Continental EnvironmentsContinental EnvironmentsTwo continental plates converge, diverge, Two continental plates converge, diverge,

or move horizontally to one anotheror move horizontally to one anotherRocks build up stressRocks build up stressMountains form and earthquakes occurMountains form and earthquakes occur

MAJOR EARTHQUAKE MAJOR EARTHQUAKE ZONESZONES

Pacific Ring of FirePacific Ring of Fire

Mid-ocean ridgesMid-ocean ridges

Eurasian-Melanesian Mountain BeltEurasian-Melanesian Mountain Belt

MAJOR EARTHQUAKES MAJOR EARTHQUAKES AREASAREAS

Fault ZonesFault Zones Intense stress along plate boundaries create Intense stress along plate boundaries create

fault zonesfault zonesPlates separate, collide, subduct or slide past Plates separate, collide, subduct or slide past

one anotherone anotherMovement from stress buildup causes major Movement from stress buildup causes major

earthquakesearthquakes

PUGET SOUND FAULT PUGET SOUND FAULT ZONESZONES

Studying EarthquakesStudying Earthquakes

Ancient Chinese Method of Studying Earthquakes

MagnitudeMagnitude

The measure of the The measure of the strength of an strength of an earthquake, earthquake, determined by determined by measuring the measuring the amount of ground amount of ground motion.motion.

Richter ScaleRichter Scale

Used for most of the Used for most of the 2020thth century. Each century. Each number represents a number represents a factor of 30 (a 5 factor of 30 (a 5 earthquake has 30 earthquake has 30 times the energy of a times the energy of a 4). We now prefer to 4). We now prefer to use the……use the……

Moment MagnitudeMoment Magnitude Based on the size of the area of fault movement, the Based on the size of the area of fault movement, the

average distance that the fault blocks move, and the average distance that the fault blocks move, and the rigidity of the rocks in the fault zone. More rigidity of the rocks in the fault zone. More accurate for large earthquakes.accurate for large earthquakes.

IntensityIntensity

Based on an earthquake’s Based on an earthquake’s effects. The effects. The Mercalli Mercalli scalescale (p. 304) uses Roman (p. 304) uses Roman numerals I-XII. Depends numerals I-XII. Depends on magnitude, distance on magnitude, distance from the epicenter, local from the epicenter, local geology, earthquake geology, earthquake duration, and human duration, and human infrastructure.infrastructure.

Charleston, SC - 1886

I & III & II

Not felt except by a Not felt except by a very few.very few.

Felt by a few persons Felt by a few persons on the upper floors on the upper floors of buildings.of buildings.

III & IVIII & IV

Felt indoors.Felt indoors.

Hanging objects Hanging objects swing.swing.

V & VIV & VI

Felt outdoors.Felt outdoors.

Felt by all, many Felt by all, many scared and run scared and run outdoors.outdoors.

VII & VIIIVII & VIII

Difficult to stand.Difficult to stand.

Damage slight in Damage slight in specially designed specially designed structures.structures.

IX & XIX & X

Damage considerable in Damage considerable in specially designed specially designed structures.structures.

Ground cracked, rails Ground cracked, rails bent.bent.

XI & XIIXI & XII

Bridges destroyed, Bridges destroyed, broad fissures in broad fissures in ground.ground.

Total destruction.Total destruction.

Earthquakes and SocietyEarthquakes and SocietyEffects on Humans, Property & InfrastructureEffects on Humans, Property & Infrastructure

How to PREPARE for an EarthquakeHow to PREPARE for an Earthquake

MAJOR TSUNAMISMAJOR TSUNAMIS

Caused by an earthquake whose epicenter is on or below the ocean floor that causing:

A rapid drop or rise in the ocean floor

OR

An underwater landslide that displaces a large volume of water

Much Safer To Be Out In The OpenMuch Safer To Be Out In The Open

Most injuries result Most injuries result from the collapse from the collapse of buildings, falling of buildings, falling objects, and flying objects, and flying glass.glass.

Other Dangers IncludeOther Dangers Include

LandslidesLandslidesFiresFiresExplosions (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 rock Loose soil and rock can vibrate like can vibrate like Jell-O.Jell-O.

KOBE SEISMOGRAPHKOBE SEISMOGRAPHTop - Station on solid groundTop - Station on solid ground

Right - Station on water Right - Station on water saturated, saturated, soft ground soft ground

LIQUEFACTIONLIQUEFACTIONKobeKobe

Quake DurationQuake Duration

A long duration moderate earthquake can A long duration moderate earthquake can cause more damage than a short one at a cause more damage than a short one at a higher magnitude.higher magnitude.

FIRES FIRES KobeKobe

Destruction to Buildings and Destruction to Buildings and PropertyProperty

STRUCTURAL DAMAGESTRUCTURAL DAMAGEKobe earthquakeKobe earthquake

CHILE – 1960CHILE – 1960Largest Recorded 9.5Largest Recorded 9.5

ALASKA- 1964ALASKA- 19649.29.2

EARTHQUAKE SAFETYPeople who live near active faults should be

ready to follow a few simple earthquake safety rules to help prevent death, injury,

and property damage

BEFOREBEFORE - - Be preparedBe prepared DURINGDURING - - Stay calmStay calmAFTERAFTER - - Stay cautiousStay cautious

Before an EarthquakeBefore an Earthquake

Be prepared. Keep an adequate supply Be prepared. Keep an adequate supply of food, water, batteries, flashlights and of food, water, batteries, flashlights and a radio.a radio.

Prepare an earthquake plan and Prepare an earthquake plan and discuss it with your family.discuss it with your family.

Learn how to turn off the gas, water, Learn how to turn off the gas, water, and electricity in your home.and electricity in your home.

During an EarthquakeDuring an Earthquake

Protect yourself by moving to a safe Protect yourself by moving to a safe position.position.

Best way is the “Triangle of Life” Best way is the “Triangle of Life” (next slide--(next slide--))

Indoors Indoors – – get under a table or if not get under a table or if not possible in a inside door frame away possible in a inside door frame away from heavy furniturefrom heavy furniture

OutdoorsOutdoors – – get away from tall get away from tall buildings, tunnels, power lines or buildings, tunnels, power lines or bridges out in the openbridges out in the open

Triangle of Life during a QuakeTriangle of Life during a Quake

Newest research shows your first best position Newest research shows your first best position to get into during a quake is next to and below to get into during a quake is next to and below the level of a heavy object – table or furniturethe level of a heavy object – table or furniture

Cover your head in bracing position Cover your head in bracing position (like shown on a plane)(like shown on a plane)

Any falling debris will hit table or furniture and Any falling debris will hit table or furniture and arc over you and you will be protectedarc over you and you will be protected

Bracing Under a TableBracing Under a TableEspecially at SchoolEspecially at School

Earthquake Warnings and Forecasts

Scientists study past earthquakes to Scientists study past earthquakes to predict predict wherewhere future earthquakes will future earthquakes will occur.occur.

There is currently There is currently no wayno way to predict to predict exactly when exactly when an earthquake will occur.an earthquake will occur.

Seismic Gaps – Areas along a fault where Seismic Gaps – Areas along a fault where stress has built up due to a decrease in stress has built up due to a decrease in

seismic activity recently but where strong seismic activity recently but where strong

earthquakes occurred in the pastearthquakes occurred in the past

Don’t be Don’t be ScaredScared, , Be Be

PreparedPrepared!!3 Days, 3 Ways3 Days, 3 Ways

Earthquake Preparedness Earthquake Preparedness Starts NOW!Starts NOW!

3days3ways.org3days3ways.org

Mr. K will show you how starting Tuesday!Mr. K will show you how starting Tuesday!