EARTHQUAKES AND PLATE TECTONICS

CHAPTER 6 SECTION 1CHAPTER 6 SECTION 1

ELASTIC REBOUND ELASTIC REBOUND THEORYTHEORY

Rocks on each side of a fault are moving.Rocks on each side of a fault are moving.

Fault is locked, rocks stop moving.Fault is locked, rocks stop moving.

Rocks on each side of a fault are stressed.Rocks on each side of a fault are stressed.

Rocks fracture and separate at weakest point.Rocks fracture and separate at weakest point.

Rocks return to original shape.Rocks return to original shape.

Elastic Rebound TheoryElastic Rebound Theory

AFTERSHOCKSAFTERSHOCKS

Original earthquake releases energy in Original earthquake releases energy in the form of vibrations called seismic the form of vibrations called seismic waves.waves.

These vibrations may increase stress in These vibrations may increase stress in other rocks along the fault.other rocks along the fault.

The increased stress on these rocks may The increased stress on these rocks may cause them to fracture and spring back.cause them to fracture and spring back.

The series of smaller tremors are called The series of smaller tremors are called aftershocks. aftershocks.

FOCUSFOCUS

Area 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 variesThe depth of the focus varies

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 A point on the earth’s surface directly above the surface directly above the focusfocus

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

PUGET SOUND FAULT PUGET SOUND FAULT ZONESZONES

MagnitudeMagnitude

STRUCTURAL DAMAGESTRUCTURAL DAMAGEKobe EarthquakeKobe Earthquake

LIQUEFACTIONLIQUEFACTIONKobeKobe

RECORDING EARTHQUAKESRECORDING EARTHQUAKES

CHAPTER 6, SECTION 2CHAPTER 6, SECTION 2

TYPES OF SEISMIC WAVESTYPES OF SEISMIC WAVES

P wavesP waves

S wavesS waves

L wavesL waves

P WAVESP WAVES

Fastest waveFastest waveFirst recorded on seismographFirst recorded on seismographTravel through solid and liquidTravel through solid and liquidCause rock particles to move together and Cause rock particles to move together and

apart along the direction of the waves.apart along the direction of the waves.

S WAVESS WAVES

Second wave to reach seismographSecond wave to reach seismographTravels through solids onlyTravels through solids onlyCause rock particles to move at right Cause rock particles to move at right

angles to the direction the wave is angles to the direction the wave is travelingtraveling

L WAVESL WAVES

Slowest moving of the three wavesSlowest moving of the three wavesAlso called surface or long wavesAlso called surface or long wavesLast to be recorded by the seismographLast to be recorded by the seismographTravel over the earth’s surface similar to Travel over the earth’s surface similar to

ocean wavesocean wavesCause the greatest damageCause the greatest damage

SEISMOGRAPHSEISMOGRAPH

A device used to measure A device used to measure seismic wavesseismic waves

LOCATING THE EPICENTER

EARTHQUAKE SCALESEARTHQUAKE SCALES

RICHTER RICHTER

MERCALLIMERCALLI

RICHTER SCALERICHTER SCALE Scale that ranges from 1-10Scale that ranges from 1-10 Each whole number increases the Each whole number increases the

magnitude of the energy 31.7 timesmagnitude of the energy 31.7 times

Largest recorded magnitude - 9.5Largest recorded magnitude - 9.5 Above 7 - Major earthquakeAbove 7 - Major earthquake Between 6 and 7 - Moderate earthquakeBetween 6 and 7 - Moderate earthquake Between 2.5 and 6 - Minor earthquakeBetween 2.5 and 6 - Minor earthquake Less than 2.5 - MicroearthquakeLess than 2.5 - Microearthquake

MERCALLI SCALEMERCALLI SCALE

Measures the intensity of the damaged Measures the intensity of the damaged caused by the earthquakecaused by the earthquake

Scale of I - XII (1-12)Scale of I - XII (1-12)

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

II. Felt by a very few persons II. Felt by a very few persons onon

the upper floors of buildings the upper floors of buildings

III. Felt indoorsIII. Felt indoors

IV. Hanging objects swingIV. Hanging objects swing

V. Felt outdoorsV. Felt outdoors

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

VII. Difficult to standVII. Difficult to stand

VIII. Damage slight in VIII. Damage slight in speciallyspecially

designed structures designed structures

IX. Damage considerable inIX. Damage considerable in specially designed specially designed

structuresstructures

X. Ground cracked, rail bentX. Ground cracked, rail bent

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

XII. Damage totalXII. Damage total

Pacific Northwest Earthquake InformationREQUEST FOR EARTHQUAKE INFORM

ATION

EARTHQUAKE SAFETY

BEFORE - Be prepared BEFORE - Be prepared DURING - Stay calmDURING - Stay calmAFTER - Stay cautiousAFTER - Stay cautious

ASSIGNMENTWORKSHEET 6.3WORKSHEET 6.3Page 111, #1-5Page 111, #1-5