Part 2Part 2: Earthquakes & Seismology: Earthquakes & Seismology (See Part 1: The Earth & Plate Tectonics for background)

Video lectures of this presentation can be viewed at: www.iris.edu/hq/programs/education_and_outreach/videos

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www.iris.edu/hq/programs/education_and_outreach/animations

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Slide show prepared by Slide show prepared by Dr. Robert Butler, University of Portland, and Jenda Johnson.Dr. Robert Butler, University of Portland, and Jenda Johnson.

Focus: or hypocenter; point within Earth where the EQ occurred.

Epicenter—Location directly above EQ on Earth’s surface.

Epicenter & Focus of Earthquakes

Why are there earthquakes? Brittle vs. ductile

Example:

Subduction-zone earthquakes occur in discrete areas on and between plates.

Why?

Watch the video lectures!

Body wavesBody waves(P and S) (P and S) travel inside travel inside Earth.Earth.

Surface waves Surface waves travel along travel along Earth’s surfaceEarth’s surface..

Body Waves and Surface Waves

While P- and S- waves radiate outward in all directions, surface waves travel along the surface of the earth and decrease in amplitude with depth.

P waves Fast

S wavesIntermediate

Surface Slow

waves

Types of seismic waves

Body waves

P waves are compressional

Activity: “Seismic Slinky—Generating P & S waves”; see notes.

ACTIVITY:

Screen GrabAnimation link in notes

S waves are shear waves

Body waves

ACTIVITY:

Screen GrabAnimation link in notes

Rayleigh & Love Waves

Surface waves

A seismograph detects and records EQs.

A seismogram is the EQ record.

How do scientists detect earthquakes?

When an earthquake occurs the seismic waves travel through the Earth to the seismic station

where the information is transmitted to distant computers.

Seismometers

Animations of horizontal and vertical seismographs and a movie of an actual seismogram being recorded during an

earthquake are on the website: http://www.iris.edu/hq/programs/education_and_outreach/animations

Screen GrabAnimation link in notes

Download one-pager, “No. 7. How Does a Seismometer Work?”http://www.iris.edu/hq/publications/brochures_and_onepagers/edu

Narrated animations of basic effect of P, S, and Surface waves on a seismic station are on:

http://www.iris.edu/hq/programs/education_and_outreach/animations

SeismicWaveBehavior—

Effect on Building: 3-Component Seismograph:

Screen GrabsAnimation link in notes

Download the impressive interactive P.C. program with other earthquakes from Alan L. Jones’ website: http://www.geol.binghamton.edu/faculty/jones/

If you don’t have a PC, you can watch the progression (and how complicated it can be) in an animated replication of a part of the computer program:http://www.iris.edu/hq/programs/education_and_outreach/animations

ACTIVITY:

Seismic waves from the 2004 Sumatran earthquake were recorded at stations all over the globe.

Screen GrabAnimation link in notes

Travel-time curvesSeismic waves from large earthquakes arrive at seismic stations around the world at predictable times.

The graph on the right (turned 90° and includes only major direct waves) shows the arrival times as continuous lines for each of the waves reflecting the pattern in the seismograms above.

(see animation “Travel-time curves”)

Animation link in notes

A seismogram is the record of an earthquake.

P waves travel about 1.7 times faster than S waves. Surface waves take their time rolling along at shallow

levels.

The difference between the arrival times of the seismic waves indicates of how far away the earthquake was.

QUESTION:

If a P wave arrived at a station 5 minutes and 45 seconds after the earthquake occurred; and the S wave arrived at the station 10 min and 30 seconds minutes after the earthquake occurred, how far away was the earthquake?

How far away was the earthquake?

Calculate S-arrival time minus P-arrival time using this graph of travel-time curves.

ACTIVITY:

How can you use this information to locate an earthquake?

ACTIVITY:

Graph of travel-time curves

Locating an Earthquake1) Determine distance of EQ

from three seismic stations by calculating the S minus P arrival times.

2) Plot them on the travel-time graph.

3) Intersection of the circles gives the location.

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ACTIVITY:

See: http://www.iris.edu/hq/programs/education_and_outreach/animations#N

How big was it? The Richter Scale

What is the Richter magnitude of this EQ?

S — P = 26 sec

Amplitude = 23mm

Magnitude = 5

How big was it? The Richter Scale

What is the Richter magnitude of this EQ?

Magnitudes and Energy of Earthquakes Download: How Often do Earthquakes Occur? Annual Numbers of EQs

What’s the message?

MOST of the energy is released by around 20 magnitude-7 and larger EQs every year.

Magnitudes and Energy of Earthquakes Download: How Often do Earthquakes Occur? Annual Numbers of EQs

What’s the message?

MOST of the energy is released by around 20 magnitude-7 and larger EQs every year.

The Earthquake Machine

Think forces, faults, and friction.

How could pulling a block of wood

with a string of rubber bands have

anything to do with earthquakes?

There are no rubber bands in the

Earth, but all solids are elastic,

including the Earth’s crust.

ACTIVITY:

ACTIVITY & ANIMATIONS are on http://www.iris.edu/hq/programs/education_and_outreach/animations/1

Earthquake Intensity is what you feel. What Controls the Level of Shaking?

• Magnitude—More energy released

• Distance—Shaking decays with distance

• Geology—Local soils amplify the shaking

• Building style—Construction, not height

• Duration of shaking

Example: 1994 Northridge EQ, M=6.7

Seismic intensity is affected by rock type.

Amplitude of oscillation

How would you expect the houses to react during an EQ?

Seismic intensity is affected by rock type.

Amplitude of oscillation increasing

Liquefaction experimentWhat happens to a structure built on a weak

foundation when an earthquake strikes?

Photos: Lily RodriguezFrom website below

For the description of this liquefaction activity:http://www.exploratorium.edu/faultline/activezone/liquefaction.html

Niigata, Japan 1964Source: National Geophysical Data Center

Building design: If the resonant frequency of a building is equal to the frequency of ground oscillation, then damage or collapse is likely.

What is resonant frequency?

Discussion: Why is building damage selective?

ResonanceOscillating buildings demonstration—3 methods.

BOSS model

Video demonstrations by John Lahr are online:

http://www.iris.edu/hq/programs/education_and_outreach/videos

Two similar demonstrations use simpler methods:

Spaghetti & Manilla file raisins……. “Boss lite”…

Screen Grabs

Building design is critical to earthquake safety

Resistance to shear is critical.

See the video lecture on Building Strength on: http://www.iris.edu/hq/programs/education_and_outreach/videos