EARTHQUAKES…EARTHQUAKES…

What is an Earthquake?What is an Earthquake?

Shaking and vibration at the surface of the earth Shaking and vibration at the surface of the earth caused by the underground movement along a caused by the underground movement along a FAULTFAULT plane. plane.

Results from a sudden release of energy in the Results from a sudden release of energy in the Earth's crust that creates Earth's crust that creates SEISMIC WAVESSEISMIC WAVES..

Tectonic plate interaction is the primary cause.Tectonic plate interaction is the primary cause.

1960 Valdivia Chile 1960 Valdivia Chile EarthquakeEarthquake

Largest Earthquake ever recordedLargest Earthquake ever recorded Moment Magnitude of Moment Magnitude of 9.59.5!!!!!!

Generated a massive tsunamiGenerated a massive tsunami 2000 killed – over $550M in damage2000 killed – over $550M in damage

This Building Was Washed in by Tsunami Wave

Ocean-Continental Convergence = Nazca Plate Ocean-Continental Convergence = Nazca Plate subducting beneath S. American Platesubducting beneath S. American Plate

122 Killed in Onagawa, Japan122 Killed in Onagawa, Japan

61 Killed Hilo, Hawaii61 Killed Hilo, Hawaii

NAZCA PLATE S. AMERICAN PLATE

TRENCHEPICENTER

EPICENTEREPICENTER The location on Earth’s The location on Earth’s surfacesurface that lies directly that lies directly

above the forces of an earthquake (The Focus).above the forces of an earthquake (The Focus).

FOCUSFOCUS The zone The zone withinwithin Earth where movement Earth where movement

along a fault produces an earthquake.along a fault produces an earthquake.

What is a FAULT?What is a FAULT? A FAULT is a fracture or zone of fractures A FAULT is a fracture or zone of fractures

between two blocks of rock. between two blocks of rock.

Faults allow the blocks to move relative to Faults allow the blocks to move relative to each other.each other.

Slow movement = “creep”Slow movement = “creep” Rapid Movement = “earthquake”Rapid Movement = “earthquake”

Faults may range in length from a few Faults may range in length from a few millimeters to thousands of kilometers. millimeters to thousands of kilometers.

3 Classifications of Faults3 Classifications of Faults

1. Normal Faults1. Normal Faults: : Rock above the fault Rock above the fault plane has moved DOWN relative to the rock plane has moved DOWN relative to the rock below. (Divergence)below. (Divergence)

Normal Fault Flash AnimationNormal Fault Flash Animation

2. Reverse (Thrust) Faults2. Reverse (Thrust) Faults: : Rock above Rock above the fault plane moves UP relative to the rock the fault plane moves UP relative to the rock below. (Convergence)below. (Convergence)

Thrust Fault Flash AnimationThrust Fault Flash Animation

3. Strike-Slip Faults3. Strike-Slip Faults: : A fault along which A fault along which the movement is horizontal. (Transform)the movement is horizontal. (Transform)

Strike-slip Fault Flash AnimationStrike-slip Fault Flash Animation

Stress = DeformationStress = Deformation

Sumatra Mega-thrust Sumatra Mega-thrust (Reverse) Fault(Reverse) Fault

Tsunami 2004, Dec. 26thTsunami 2004, Dec. 26th

http://www.news.cornell.edu/http://www.news.cornell.edu/releases/Jan05/tsunamiVid640.htmlreleases/Jan05/tsunamiVid640.html

SUMATRA TSUNAMI 2004SUMATRA TSUNAMI 2004

Sumatra Tsunami 2004Sumatra Tsunami 2004

So….So….

How do Seismologists How do Seismologists measure the strength of measure the strength of

anan

EARTHQUAKE?EARTHQUAKE?

Giuseppe Mercalli – 1902

Qualitative Data

Charles Richter – 1936

Quantitative Data

Mercalli Intensity(at epicenter)

Witness Observations

I Felt by very few people; barely noticeable.

II Felt by a few people, especially on upper floors.

III Noticeable indoors, especially on upper floors, but may not be recognized as an earthquake.

IV Felt by many indoors, few outdoors. May feel like heavy truck passing by.

VFelt by almost everyone, some people awakened. Small objects moved. Trees and poles may shake.

VIFelt by everyone. Difficult to stand. Some heavy furniture moved, some plaster falls. Chimneys may be slightly damaged.

VIISlight to moderate damage in well built, ordinary structures. Considerable damage to poorly built structures. Some walls may fall.

VIIILittle damage in specially built structures. Considerable damage to ordinary buildings, severe damage to poorly built structures. Some walls collapse.

IXConsiderable damage to specially built structures, buildings shifted off foundations. Ground cracked noticeably. Wholesale destruction. Landslides.

XMost masonry and frame structures and their foundations destroyed. Ground badly cracked. Landslides. Wholesale destruction.

XITotal damage. Few, if any, structures standing. Bridges destroyed. Wide cracks in ground. Waves seen on ground.

XII Total damage. Waves seen on ground. Objects thrown up into air.

Modified Mercalli Scale (Qualitative)

Richter Scale is Logarithmic: Richter Scale is Logarithmic: Each magnitude is 10x stronger than the Each magnitude is 10x stronger than the

previous.previous.

MOMENT MAGNITUDE MOMENT MAGNITUDE

Invented in 1977 by Hiroo KanamoriInvented in 1977 by Hiroo Kanamori

Moment is a measure of earthquake size Moment is a measure of earthquake size that takes into account how much the fault that takes into account how much the fault slips and over how much area. slips and over how much area.

Identical to Richter for EQ’s 7 and smaller.Identical to Richter for EQ’s 7 and smaller.

More precise for measuring larger EQ’s.More precise for measuring larger EQ’s.

INTENSITY vs. MAGNITUDEINTENSITY vs. MAGNITUDE The MAGNITUDE of an EQ is how much energy The MAGNITUDE of an EQ is how much energy

is released during the event.is released during the event.

INTENSITY describes the perceptible moving, INTENSITY describes the perceptible moving, shaking and damage experienced during the shaking and damage experienced during the event.event.

Two EQ’s can have same magnitude, but very Two EQ’s can have same magnitude, but very different intensity depending upon such different intensity depending upon such variables as location relative to the epicenter, variables as location relative to the epicenter, type of bedrock and soil in the region, as well type of bedrock and soil in the region, as well as the type of fault where the EQ occurred.as the type of fault where the EQ occurred.

How are Earthquakes How are Earthquakes Recorded?Recorded?

A A seismogramseismogram is a record written by a is a record written by a seismographseismograph in response to ground motions produced by an in response to ground motions produced by an earthquake, explosion, or other ground-motion sources earthquake, explosion, or other ground-motion sources

How do Seismologists use this How do Seismologists use this Data?Data?

Seismic WavesSeismic Waves

1) Surface Waves1) Surface Waves: Waves that travel : Waves that travel alongalong

Earth’s outer layer.Earth’s outer layer.

2) Body Waves2) Body Waves: Travel through Earth’s : Travel through Earth’s Interior…….2 KindsInterior…….2 Kinds

P- WavesP- Waves

S-WavesS-Waves******Identified by how they travel through the materials within the Identified by how they travel through the materials within the

EarthEarth

Surface Waves Surface Waves Love WavesLove Waves The first kind of surface wave is called a The first kind of surface wave is called a Love waveLove wave, ,

named after A.E.H. Love, a British mathematician who named after A.E.H. Love, a British mathematician who worked out the mathematical model for this kind of worked out the mathematical model for this kind of wave in 1911. It's the fastest surface wave and moves wave in 1911. It's the fastest surface wave and moves the ground from side-to-side.the ground from side-to-side.

Surface WavesSurface WavesRayleigh WavesRayleigh Waves

The other kind of surface wave is the The other kind of surface wave is the Rayleigh waveRayleigh wave, named for , named for John William Strutt, Lord Rayleigh, who mathematically predicted John William Strutt, Lord Rayleigh, who mathematically predicted the existence of this kind of wave in 1885. A Rayleigh wave rolls the existence of this kind of wave in 1885. A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Most of the shaking in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves.much larger than the other waves.

P-Waves (Compression)P-Waves (Compression)

S-Waves (Shear)S-Waves (Shear)

P-WavesP-Waves S-WavesS-Waves

PPrimary Wavesrimary Waves SSecondary Wavesecondary Waves

FasterFaster SSlowerlower

Compression “Compression “PPush” ush” WaveWave

““SShear” Waveshear” Waves

Direction of Particle MovementDirection of Particle Movement

((PPush/ush/PPull)ull)Direction of Particle MovementDirection of Particle Movement

((SSide to ide to SSide)ide)

Moves through liquids Moves through liquids and solidsand solids

SStop when they reach a top when they reach a liquid medium liquid medium

P Wave Shadow ZoneP Wave Shadow Zone

S Wave Shadow ZoneS Wave Shadow Zone

ESRT Time/Travel Graph P and S WavesESRT Time/Travel Graph P and S Waves

Sample Regents ProblemSample Regents Problem

ESRT Time/Travel GraphESRT Time/Travel GraphS - P = Lag Time (3 min.)S - P = Lag Time (3 min.)

Calculate Distance from Seismic Station to Calculate Distance from Seismic Station to Epicenter of EQ Using ESRT Epicenter of EQ Using ESRT

Let’s try it another way…Let’s try it another way…

ESRT Time/Travel GraphESRT Time/Travel GraphP and S WavesP and S Waves

7 min

Here’s Another One…Here’s Another One…8/07 test8/07 test

Take difference between P arrival

and S arrival

And…..And…..

Let’s Be Virtual Let’s Be Virtual Seismologists!Seismologists!

Virtual Earthquake - An IntroductionVirtual Earthquake - An Introduction