18
Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard maps? By careful study of earthquake effects and damage, geologists now understand that local rock and soil conditions are very important. The same earthquake can cause very different effects in nearby locations if the geologic layers beneath those locations are different. Simply stated, some locations are more hazardous than others. Geologists develop earthquake-hazard maps to show how a particular hazard, like liquefaction, changes over a mapped area (Figure 1) because of local geologic conditions (Figure 2). Governmental agencies use earthquake-hazard maps for land-use and emergency-management planning. Wise home buyers can use earthquake-hazard maps, among other considerations, to decide where to live (and where not to live). Figure 2: Shaking sands can take down large buildings as shown in the photograph of buildings tilted by ground failure caused by liquefaction. Nigata, Japan earthquake (www.noaa.gov) NGSS Science Standards From Molecules to Organisms—Structures and Processes: MS-LS1-8 Ecosystems—Interactions, Energy, and Dynamics: MS-LS2-4 Motion and Stability—Forces and Interactions: HS-PS2-1, MS-PS2-2 Energy HS-PS3-2, MS-PS3-5, HS-PS4-1, MS-PS4-2 Earth’s Systems: HS-ESS2-1, MS-ESS2-2, HS-ESS2-2 Earth and Human Activity: HS-ESS3-1, MS-ESS3-2 Animations about Alaska earthquakes: Alaska: The Great Alaska Earthquake of 1964: www.iris.edu/hq/inclass/animation/231 Alaska: Tectonics and Earthquakes: www.iris.edu/hq/inclass/animation/232 Animations about earthquake ground shaking and effects: Earthquake Intensity: What controls the shaking you feel during an earthquake? www.iris.edu/hq/inclass/animation/517 Buildings & Bedrock: Effects of amplification & liquefaction: www.iris.edu/hq/inclass/animation/111 Liquefaction during the 1906 San Francisco quake: www.iris.edu/hq/inclass/animation/112 1 Field Merrill Campbell Airstrip International Airport Anchorage Stevens Ted P o tter C r e ek L it tle Ra bbit Creek L it tle R ab bi t Creek Ra b b it Cr e e k R ab bit C re e k C a m p be l l Creek N orth F o rk Li ttle C a m pbell Creek M id d le Fo r k Little C a m p bell Creek So uth F o rk Campbell C r e ek F i s h C r e ek C he ste r Cree k S h i p C r ee k Ship Cree Little Surv i v a l C r e e k Fu rr o w Cr e ek S o u th F ork L i ttle C a m p b e l l C r e e k N ort h F ork C a m p bel l C r e e k S o u t h F o rk C hester Cree k H o od C r e e k A.A.R. A.A.R. RASPBERRY ROAD DIMOND BOULEVARD W KLATT ROAD OLD KLATT ROAD E KLATT ROAD POSTMARK DRIVE GLENN HIGHWAY P O T TE R VALLE Y R OAD SE WARD HIGHWA Y OLD SEWA RD HI G H W A Y RABBIT C R EEK ROA D DE ARMOUN ROAD CL AR KS R OA D GOLDENVIEW DRIVE S E WARD HIGHWAY OLD SEWARD HIGHWAY ELMORE ROAD BIRCH ROAD HUFFMAN ROAD HILLSIDE DRIVE ABBOTT ROAD O'MALLEY ROAD S O UTH P O R T D RIVE W 100TH AVENUE C ST R E E T JODHPUR STREET SAND LAKE ROAD JEWEL LAKE ROAD M I N N E S O T A D R I V E DIMOND BOULEV A RD KINCAID ROAD NORTHWOOD DRIVE C STREET E 68TH AVENUE LAKE OTIS PARKWAY ABBOTT LOOP ROAD DOWLING ROAD OLD SEWARD HIGHWAY SEWARD HIGHWAY INTERNATIONAL AIRPO RT ROAD ARCTIC BOULEVARD SPE N A RD RO A D BENSON BO ULE V ARD A S T R E E T C STREET FIREWEED LANE TUDOR ROAD D E N A L I S T R E E T 36TH AVENUE LAKE OTIS PARKWAY 3RD AVENUE 6TH AVENUE 10TH AVENUE 15TH AVENUE 5TH AVENUE BLUF F ROAD BRAGAW STREET BONIFACE PARKWAY DEBARR ROAD GLENN HIGHWAY MULDOON ROAD NORTHERN LIGHTS BOULEVARD BAXTER ROAD TUDOR ROAD WISCONSIN STREET AERO AVENUE NORTHERN LIGHTS BOULEVARD Elmendorf Air Force Base Fort Richardson Military Reservation Turnagain Arm Knik Arm ZONE 2 - (Moderately-Low Ground Failure Susceptibility) ZONE 3 - (Moderate Ground Failure Susceptibility) ZONE 4 - (High Ground Failure Susceptibility) ZONE 5 - (Very High Ground Failure Susceptibility) ZONE 1 - (Lowest Ground Failure Susceptibility) 5 Map Prepared By: GIS Services Data, Projects & Procurement Division Information Technology Department Municipality of Anchorage December, 2006 Anchorage Bowl Seismic Chugach State Park Figure 1: Seismic landslide hazard map for Anchorage, Alaska. A page-size map of this is available on page 18 of this document with links to a hazard assessment pamphlet. See Activity 2 on Page 3.

Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

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Page 1: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

Earthquake Hazard Maps & LiquefactionIncludes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction

What are earthquake-hazard maps?By careful study of earthquake effects and damage, geologists now understand that local rock and soil conditions are very important. The same earthquake can cause very different effects in nearby locations if the geologic layers beneath those locations are different. Simply stated, some locations are more hazardous than others. Geologists develop earthquake-hazard maps to show how a particular hazard, like liquefaction, changes over a mapped area (Figure 1) because of local geologic conditions (Figure 2). Governmental agencies use earthquake-hazard maps for land-use and emergency-management planning. Wise home buyers can use earthquake-hazard maps, among other considerations, to decide where to live (and where not to live).

Figure 2: Shaking sands can take down large buildings as shown in the photograph of buildings tilted by ground failure caused by liquefaction. Nigata, Japan earthquake (www.noaa.gov)

NGSS Science Standards• From Molecules to Organisms—Structures and

Processes: MS-LS1-8• Ecosystems—Interactions, Energy, and

Dynamics: MS-LS2-4• Motion and Stability —Forces and Interactions:

HS-PS2-1, MS-PS2-2• Energy HS-PS3-2, MS-PS3-5, HS-PS4-1,

MS-PS4-2 • Earth’s Systems: HS-ESS2-1, MS-ESS2-2,

HS-ESS2-2• Earth and Human Activity: HS-ESS3-1,

MS-ESS3-2

Animations about Alaska earthquakes:

Alaska: The Great Alaska Earthquake of 1964: www.iris.edu/hq/inclass/animation/231

Alaska: Tectonics and Earthquakes: www.iris.edu/hq/inclass/animation/232

Animations about earthquake ground shaking and effects:Earthquake Intensity: What controls the shaking you feel during an earthquake?

www.iris.edu/hq/inclass/animation/517Buildings & Bedrock: Effects of amplification & liquefaction: www.iris.edu/hq/inclass/animation/111Liquefaction during the 1906 San Francisco quake: www.iris.edu/hq/inclass/animation/112

1

Lake

Lake

Chen

ey

Lake O'

Reflection

Lake

University

Little

Campb ell

Lake

DeLon g

Lake

Lake

Baxter

Bog

The Hills

Lake

Hideaway

Bayshore

Lake

Campb ell

Birch

Lake

Sundi

Jewel

Sand Lake

Strawberry

Lake

TakuLake

Blueberry

Lake

Conners

Lake

Meadow

Lake

Lake

Bentzen

Lake

Delaney

Lake

Tina

Lake

Hood

Spenard

Lake

Jon es

Lake

Lagoo n

Westch es ter

Otis

Lake

Goose

Lake

Lake

Hills trand

Pon d

Waldron

Lake

Lake

Lake

Basher

Lakes

Lake

Lake

Chen

ey

Lake O'

Reflection

Lake

University

Little

Campb ell

Lake

DeLon g

Lake

Lake

Baxter

Bog

The Hills

Lake

Hideaway

Bayshore

Lake

Campb ell

Birch

Lake

Sundi

Jewel

Sand Lake

Strawberry

Lake

TakuLake

Blueberry

Lake

Conners

Lake

Meadow

Lake

Lake

Bentzen

Lake

Delaney

Lake

Tina

Lake

Hood

Spenard

Lake

Jon es

Lake

Lagoo n

Westch es ter

Otis

Lake

Goose

Lake

Hills trand

Pon d

Waldron

Lake

Lake

Lake

Basher

Lakes

Mosqu ito

Field

Merrill

CampbellAirstrip

InternationalAirport

AnchorageStevensTed

Potter Creek

Little Rabbit Creek

Little Rabbit Creek

Rabb

it

Creek

Rabbit Creek

C ampbel l Cree

k

North Fork Li ttle Ca m pbell Creek

Mid

dle Fork Little Cam p bell Creek

South F o rk Campbell Creek

Fish Cre

ek

C hester Creek

S h ip Cree k

Ship C

reek

Little Survival Cre e k

Furrow Creek

South Fork Little Campbel l Cree k

North Fork Campbell Creek

Sou th F o rk Chester Creek

Hoo

d C

re

e k

Matanuska - Susitna Borough

Municipality of Anchorage (indefinite boundary)

Municipality of Anchorage (indefinite boundary)

Kenai Peninsula Borough

A.A.R.

A.A.R.

RASPBERRY ROAD

DIMOND BOULEVARD

W KLATT ROADOLD KLATT ROAD

E KLATT ROAD

POSTM

AR

K D

RIV

E

GLENN HIGHWAY

POTTE R VALLEY ROAD

SEWARD HIGHW

AY

OLD SEWARD

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WAY

RABBIT CR EEK ROAD

DE ARMOUN ROAD

CL ARKS R OAD

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IEW

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IVE

SEWARD HIG

HWAY

OLD SEWARD HIGHW

AY

ELM

OR

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HUFFMAN ROAD

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E

ABBOTT ROAD

O'MALLEY ROAD

SO

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T DRIVE

W 100TH AVENUE

C S

TRE

ET

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HP

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OA

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JEW

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IVE C

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LAKE

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AR

KW

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36TH AVENUE

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AR

KW

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6TH AVENUE

10TH AVENUE

15TH AVENUE

5TH AVENUE

BLUFF ROAD

BRA

GA

W S

TREE

T

BON

IFA

CE

PA

RKW

AY

DEBARR ROAD

GLENN HIGHWAY

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BAX

TER

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TUDOR ROADWIS

CO

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TRE

ET

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AVE

NU

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NORTHERN LIGHTS BOULEVARD

Elmendorf Air Force Base

Fort Richardson

Military Reservation

Knik Arm

Turnagain Arm

Turnagain Arm

Knik A

rm

This map is derived from Geographic Information Systems data developed and maintained by the Municipality of Anchorage ("MOA"). This map is not

the official representation of any of the information included and is made available to the public solely for informational purposes. This map may

be outdated, inaccurate and may omit important information. Do not rely on this information. The Municipality will not be liable for

losses arising from errors, inaccuracies or omissions in the map.

ZONE 2 - (Moderately-Low Ground Failure Susceptibility)

ZONE 3 - (Moderate Ground Failure Susceptibility)

ZONE 4 - (High Ground Failure Susceptibility)

ZONE 5 - (Very High Ground Failure Susceptibility)

ZONE 1 - (Lowest Ground Failure Susceptibility)

50 0.4 0.80.2

Miles

Map Prepared By: GIS Services

Data, Projects & Procurement DivisionInformation Technology Department

Municipality of Anchorage

December, 2006

Anchorage Bowl

Seismic

Chugach State Park

Figure 1: Seismic landslide hazard map for Anchorage, Alaska. A page-size map of this is available on page 18 of this document with links to a hazard assessment pamphlet. See Activity 2 on Page 3.

Page 2: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

Hazard Map Activity 1: Earthquakes and Ground Shaking Amplification (Demo)Ground shaking is the primary cause of earthquake damage to man-made structures. The amplitude of ground shaking is affected by the near-surface geology (Figure 3). Hard bedrock experiences much less violent ground shaking than does soft sedimentary layers while loose sediments greatly amplify ground shaking. Structures built on loose sediments are much more likely to experience damage during earthquake shaking than would the same structures built on bedrock

Procedure:• Pace a small heavy object on the cinder block and another

on the gravel.• Strike the cinder block with a hammer and observe.• Repeat with the pan of gravel and observe.

Questioning:What happens when the energy of a “seismic” P wave passes

through each sample material?What could each material sample represent in a real-world

setting?What features of good building design help protect buildings in

areas susceptible to ground amplification?

Materials:• Cinderblock to simulate bedrock• Pan with aquarium gravel to simulate

loose alluvium or soil “geologic Jell-O”• Small heavy object such as a weight, film

canister with sand

2

Figure 3: Image on left from www.iris.edu. Images on right from : John Clague, Chris Yorath, Richard Franklin, and Bob Turner, 2006, At Risk: Earthquakes and Tsunamis on the West Coast; Tricouni Press

Landslidepotential

Amplification& Liquefaction Amplification

Why does ground shaking from an earthquake change so much with location?

1 2 3

(Cla

gue

et a

l, 20

06)

TIME

Mild

Mild

Moderate

Severe

Strong

Strong

Poorly consolidated

sediment

Solidbedrock

Solidbedrock

Well-consolidated

sediment

Poorly consolidated

sediment

Water-saturatedsand & mud

Ampli�cation—Tall buildings on thick uncon-solidated sediments (1 & 2) such as river deltas or ocean shorelines, will be more strongly shaken than those lying directly on bedrock (3). Low-frequency, long-period seismic waves are ampli�ed as they enter the thick sediment pile. Tall buildings resonate with high-amplitude, low-frequency seismic waves (1), but if the waves are high-amplitude but higher-frequency (2), smaller buildings will be a�ected.

Liquefaction & Seismic Landslides—Liquefaction of water-saturated silt or sand may cause the ground to lose strength, fracture, and slide downhill during an earthquake, damaging or destroying buildings and other human works.

The �gure below shows that seismic waves traversing solid bedrock have low amplitude & high frequency. In weaker less-consolidated material, seismic waves oscillate with higher amplitude but with a lower frequency. Imagine dropping a rock on concrete and recording the vibration compared to dropping a rock on a vat of Jello©.

Page 3: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

3

Hazard Map Activity 2: Seismic LandslidesDemonstration: Earthquakes and Seismic Landslides

Earthquake ground shaking can cause even gently sloping areas to slide when those same areas would be stable under normal conditions. An area that is slightly unstable without earthquake ground shaking is very likely to slide during prolonged earthquake shaking. During the 1964 Great Alaska earthquake, seismic landslides caused major damage to sloping areas along Knik Arm, Ship Creek, and Chester Creek that are underlain by layers of clay and silt .

Materials:• Pan or tray with edges• 500 ml or more gravel or any other small

sediments• Paper towel tube• Monopoly© sized buildings

Procedure: • Place the paper towel tube upright in the center

of the pan. Carefully pour the sediments into the tube. Lift the paper tube allowing the sediments to fall out into a symmetrical cone demonstrating the material’s angle of repose. This angle serves as a constant for the steepness of a slope for a particular material – undisturbed.

• Carefully place one or more houses onto the slope.• Explain that an earthquake can cause the materials

on a slope to become unstable by disturbing the cohesion that holds soil particles together.

• Gently tap the pan with your hand or a ruler to simulate an earthquake and watch the hill slope “fail” or collapse.

Extensions: Try using different sediments or combinations of sediments. Use water to help over-steepen the hillside, or replicate ground saturation.

Background on Shake MapsA USGS informational paper called “ShakeMaps”—Instant Maps of Earthquake Shaking” is available from: https://pubs.usgs.gov/fs/2000/fs103-00/

Figure 4 : In this March 1964 photo released by the U.S. Geological Survey, the Govern-ment Hill Elementary School is shown torn in half by a landslide during the magnitude 9 earthquake in Anchorage, Alaska. (See link to animation about the 1964 earthquake on Page 1.)

Figure 5: Seismic landslide effects in the Turnagain Heights area, Anchorage, Alaska, caused by the 1964 earthquake.

Page 4: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

What happens to filled land when an earthquake shakes it up? Try this simple experiment to see.

What do I do?Fill the pan with sand: the deeper the better.

Put the pan on a table. Then pour in water to just below the surface of the sand.

Wiggle the skinny end of the brick down into the wet sand so it stands up like a building would.

Now, very gently, repeatedly tap the side of the pan with a mallet and notice what happens to the sand and the brick.

What’s going on?Did the sand get all squishy and the brick fall over? Allow a mixture of sand and water to sit for a while and the sand grains will settle until they touch each other. There will be water in cavities between the grains, but the mixture will behave as a solid.

When you shear or squeeze the sand (essentially what you are doing by striking the container with a hammer) you are trying to push the sand particles closer together. To do this, the particles have to push the water between them out of their way, just like what happens when you squeeze saturated sand in your hand or what happens to the sand under your feet as you walk close to the water on a beach.

In the case of an earthquake (striking the container with a hammer), the squeezing done by the shockwave happens very quickly and the water does not have time to flow out of the way of the sand particles. This results in the particles pushing on the water and causing an increase in water pressure as the particles try to move into a denser configuration.

This increased pressure causes the force at the contact points between the sand particles to decrease, and if the pressure is high enough it can reduce the interparticle forces to zero, essentially trying to “float” the sand particles away from each other for a very short time. This is liquefaction. The loss of strength occurs because there is no contact between the grains of sand and you basically have a mixture of sand suspended in water for a short time.

Materials• l Metal or heavy plastic pan—full-sized

loaf pans work fine• l Sand• l Water• l smooth brick• l rubber mallet

Hazard Map Activity 3: Liquefaction Demonstration & Student Activity (next page)Demo on th is page used with permission from http://www.exploratorium.edu/

Liquefaction is a phenomenon where water-saturated sand and silt take on the characteristics of a dense liquid during the intense ground shaking of an earthquake. The strength of loose sand or silt layers comes from friction between the grains. During shaking, these grains can lose contact and the space between grains is occupied by water. The resulting viscous fluid has little strength, and water-saturated sand and silt layers may flow to fill cracks in adjacent stronger layers or even flow onto the surface.

4

OptionalAnother demonstration of liquefaction uses two pie pans containing sand. One pan is dry, the other is saturated with water, but not covering the surface. Place a weight in each pan. Ask students to predict what will happen to the weight when an earthquake shakes the pan. Tap each pan with a ruler. Ask students to explain why there was such a big difference between the two pans. What does water do to the sand grains? What are the implications for building in an area identified as being at risk for liquefaction? What can be done to help protect structures built in areas prone to liquefaction?

Gently tapping the container vibrates the sand causing liquefac-tion. With repeated taps, the brick will settle.

Page 5: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

Liquefaction—Individual student activityBy Chris Hedeen, Oregon City High School, Oregon City OR

What do I need?• Clear plastic cups• Sand• Water• Washers (1” or larger) • Coins may be used

What do I do?Instructions and discussion are intercalated in the Student Worksheets on the next pages.Teacher answer key begins on page 12 of this document.

Clear plastic cup & washers (coins may be used)

plus

sand & water

Background on LiquefactionInformation on “Liquefaction: What it is and what to do about it” can be downloaded from: https://eeri.org/wp-content/uploads/store/Free%20PDF%20Downloads/LIQ1.pdf

5

Page 6: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

Liquefaction

A common cause of damage during earthquakes is the result of liquefaction of the soil. When earthquake vibrations pass through sand or silt, which has a high liquid content, the soil loses the properties of a solid and takes on those of a dense liquid, like quicksand or pudding. The solid strength sand or silt comes from the friction between the grains touching each other. As shaking continues, the pressure of the water between the grains increases until the pore pressure almost equals the external pressure on the soil. At this point the grains spread apart and, after sufficient strength is lost, the sand and water flows.

Procedures Model 1Obtain a small plastic or paper cup. Fill it three-quarters full with dry sand (sediment). Place several coins in the sediment so they resemble vertical walls of buildings constructed on a substrate of uncompacted sediment. This is Model 1.

Observe what happens to Model 1 when you simulate an earthquake by lightly tapping the cup on counter while you also rotate it counter clockwise.

Answer all questions with complete sentences for full credit.

1. What happened to the vertically positioned coins in the uncompacted sediment of Model 1 when you simulated and earthquake?

2. Why does this happen?

Name:_________________

SW-1

Page 7: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

Model 2

Remove the coins from model one, and add a small bit of water to the sediment in the cup so that it is moist (but not soupy). Press down on the sediment in the cup so that it is well compacted, and then place the coins into this compacted sediment just as you placed them in Model 1 earlier. Simulate an earthquake as you did for Model 1, and then answer questions 2 and 3.

1. What happened to the vertically positioned coins in the compacted sediment of Model 2 when you simulated an earthquake?

2. Based in your experimental Models 1 and 2, which kind of Earth material is more hazardous to build on in an earthquake-prone regions: compacted sediment or uncompacted sediment? (Justify your answer by citing the evidence from your experimental models.)

3. Consider the moist compacted sediment in Model 2. Do you think this material would become more hazardous to build on, or less hazardous to build on, if it became totally saturated with water during the rainy season? To find out and justify your answer, design and conduct an experimental model of your own. Call it Model 3

On the next page, write out your question (objective) and procedures on next page before conducting the experiment.

Name:_______________________________

SW-2

Page 8: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

Question:

Procedures:

1. What happened to the vertically positioned coins in the compacted sediment that is saturated with water when you simulated an earthquake?

2. What will the effects of liquefaction will be on buildings?

3. Where would liquefaction be likely to occur?

Write a statement (100-150 words) that summarizes how water in a sandy substrate beneath a home can be beneficial or hazardous. Justify your reasoning with the reference to your experimental models.

Name:______________________________

SW-3

Page 9: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

Loma Prieta Earthquake

San Francisco is located in a tectonically active region, so it occasionally experiences strong earthquakes. Figure 1 is a map showing the kinds of Earth materials upon which buildings have been constructed in a portion of San Francisco. These materials include hard compact Franciscan Sandstone, uncompacted beach and dune sands, river gravel, and artificial fill. The artificial fill is mostly debris from buildings destroyed in the great 1906 earthquake that reduced large portions of the city to blocks of rubble. Also note that three locations have been labeled X, Y, and Z on Figure 1. Imagine that you have been hired by an insurance company to asses what risk there may be in building newly constructed apartment buildings located at X, Y, and Z on Figure 1. Your job is to infer whether the risk of property damage during strong earthquakes is low (little or no damage expected) or high (damage can be expected). All that you have as a basis for reasoning is Figure 1 and knowledge of your experiments with the liquefaction models.

1. In relation to the seismograms (Figure 2), rank the seismograms according to the amount of shaking.

_____ X _____ Y _____ Z

Figure 1 Map of the nature and distribution of Earth mate-rials on which buildings and roads have been constructed for a portion of San Francisco, California.

Figure 2 Seismograms recorded at Stations X, Y, and Z, for a strong (Richter Magnitude 4.6) aftershock of the Loma Prieta, Cali-fornia, earthquake. During the earthquake, little damage occurred at X, but significant damage to houses occurred at Y and Z.

Name:_________________

SW-4

Page 10: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

2. What is the risk at location X? Why?

3. What is the risk at location Y? Why?

4. What is the risk at location Z? Why?

On October 17, 1989, just as Game 3 of the World Series was about to start in San Francisco, a strong earthquake occurred at Loma Prieta, California, and shook the entire San Francisco Bay area. Seismographs at locations X, Y, and Z (Figure 1) recorded the shaking, and resulting seismographs are shown in Figure 2.

Use complete sentences for full credit.

5. The Loma Prieta earthquake caused no significant damage at location X, but there was moderate damage to buildings at location Y and severe damage at location Z. Explain how this damage report compares to your predictions of risk in

Questions 1, 2, and 3.

SW-5

Page 11: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

6. The Loma Prieta earthquake shook the entire San Francisco Bay region. Yet Figure 2 is evidence that the earthquake had very different effects on properties located only 600 m, apart. Explain how the kind of substrate (uncompacted vs. firm and compacted) on which buildings are constructed influences how much the buildings are shaken and damaged in an earthquake

7. Imagine that you are a member of the San Francisco City Council. What actions could you propose to mitigate (decrease the probability of ) future earthquake hazards like the damage that occurred at locations Y and Z in the Loma Prieta

earthquake?

SW-6

Page 12: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

Liquefaction - KEY

A common cause of damage during earthquakes is the result of liquefaction of the soil. When earthquake vibrations pass through sand or silt, which has a high liquid content, the soil loses the properties of a solid and takes on those of a dense liquid, like quicksand or pudding. The solid strength sand or silt comes from the friction between the grains touching each other. As shaking continues, the pressure of the water between the grains increases until the pore pressure almost equals the external pressure on the soil. At this point the grains spread apart and after sufficient strength is lost the sand and water flows.

Procedures Model 1Obtain a small plastic or paper cup. Fill it three-quarters full with dry sand (sediment). Place several coins in the sediment so they resemble vertical walls of buildings constructed on a substrate of uncompacted sediment. This is Model 1.

Observe what happens to Model 1 when you simulate an earthquake by lightly tapping the cup on counter while you also rotate it counter clockwise.

Answer all questions with complete sentences for full credit. 1. What happened to the vertically positioned coins in the uncompacted sediment of Model 1 when you simulated and earthquake?

The coins tip horizontally and sank slightly into the sediment. Overall movement isn’t great.

2. Why does this happen?

Answers will vary. The vibrations of the shaking cause both the particles of the sediment and the coins to shift.

AK-1

Page 13: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

Model 2

Remove the coins from model one, and add a small bit of water to the sediment in the cup so that it is moist (but not soupy). Press down on the sediment in the cup so that it is well compacted, and then place the coins into this compacted sediment just as you placed them in Model 1 earlier. Simulate an earthquake as you did for Model 1, and then answer questions 2 and 3.

2. What happened to the vertically positioned coins in the compacted sediment of Model 2 when you simulated an earthquake?

Answers will vary. There was less displacement of the coins.

3. Based in your experimental Models 1 and 2, which kind of Earth material in more hazardous to build on in an earthquake-prone regions: compacted sediment or uncompacted sediment? (Justify your answer by citing the evidence from your experimental models.)

Answers will vary. Building on compacted sediment is going to less hazardous. Answers should include evidence from models 1 and 2.

4. Consider the moist compacted sediment in Model 2. Do you think this material would become more hazardous to build on, or less hazardous to build on, if it became totally saturated with water during the rainy season? (To find out and justify your answer, design and conduct another experimental model of your own.) Call it Model 3

The more saturated the soil, the more hazardous it becomes to build on it.

On the next page, write out your question (objective) and procedures before conducting the experiment.

KEY

AK-2

Page 14: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

Question:

Procedures:

1. What happened to the vertically positioned coins in the compacted sediment that is saturated with water when you simulated an earthquake?

2. What will the effects of liquefaction will be on buildings?

3. Where would liquefaction be likely to occur?

Write a statement (100-150 words) that summarizes how water in a sandy substrate beneath a home can be beneficial or hazardous. Justify your reasoning with the reference to your experimental models.

KEY

AK-3

Page 15: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

Loma Prieta Earthquake

San Francisco is located in a tectonically active region, so it occasionally experiences strong earthquakes. Figure 1 is a map showing the kinds of Earth materials upon which buildings have been constructed in a portion of San Francisco. These materials include hard compact Franciscan Sandstone, uncompacted beach and dune sands, river gravel, and artificial fill. The artificial fill in mostly debris from buildings destroyed in the great 1906 earthquake that reduced large portions of the city to blocks of rubble. Also note that three locations have been labeled X, Y, and Z on Figure 1. Imagine that you have been hired by and insurance company to asses what risk there may be in building newly constructed apartment buildings located at X, Y, and Z on Figure 1. Your job is to infer whether the risk of property damage during strong earthquakes in low (little or no damage expected) or high (damage can be expected). All that you have as a basis for reasoning is Figure 1 and knowledge of your experiments with the liquefaction models.

1. In relation to the seismograms (Figure 2), rank the seismograms according to the amount of shaking.

___3__ X ___1__ Y ___2__ Z

Figure 1 Map of the nature and distribution of Earth materi-als on which buildings and roads have been constructed for a portion of San Francisco, California.

Figure 2 Seismograms recorded at Stations X, Y, and Z, for a strong (Richter Magnitude 4.6) aftershock of the Loma Prieta, California, earthquake. During the earthquake, little damage occurred at X, but significant damage to houses occurred at Y and Z.

KEY

AK-4

Page 16: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

2. What is the risk at location X? Why? Low – rocks are sandstone

3. What is the risk at location Y? Why? High –bed rock is modern beach and dune sand

4. What is the risk at location Z? Why? High – bed rock is artificial fill, likely uncompacted

On October 17, 1989, just as Game 3 of the World Series was about to start in San Francisco, a strong earthquake occurred at Loma Prieta, California, and shook the entire San Francisco Bay area. Seismographs at locations X, Y, and Z (Figure 1) recorded the shaking, and resulting seismographs are shown in Figure 2.

Use complete sentences for full credit.

5. The Loma Prieta earthquake caused no significant damage at location X, but there was moderate damage to buildings at location Y and severe damage at location Z. Explain how this damage report compares to your predictions of risk in Questions 1, 2, and 3.

Answers will vary. Greatest damage in those areas that have highest risk for liquefaction (uncompacted artificial fill) and least damage in areas that have well compacted rocks (sandstone).

KEY

AK-5

Page 17: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

6. The Loma Prieta earthquake shook the entire San Francisco Bay region. Yet Figure 2 is evidence that the earthquake had very different effects on properties located only 600 m apart. Explain how the kind of substrate (uncompacted vs. firm and compacted) on which buildings are constructed influences how much the buildings are shaken and damaged in an earthquake.

Answers will vary. Answer should include a discussion of better compacted substrates making better foundation materials as they do not experience liquefaction. When earthquake vibrations pass through sand or silt, which has a high liquid content, the soil loses the properties of a solid and takes on those of a dense liquid, like quicksand or pudding. The solid strength sand or silt comes from the friction between the grains touching each other. As shaking continues, the pressure of the water between the grains increases until the pore pressure almost equals the external pressure on the soil. At this point the grains spread apart and after sufficient strength is lost the sand and water flows.

7. Imagine that you are a member of the San Francisco City Council. What actions could you propose to mitigate (decrease the probability of ) future earthquake hazards like the damage that occurred at locations Y and Z in the Loma Prieta earthquake?

Answers will vary. Possible answers include: different building codes in different areas, evacuation plans for existing buildings, retrofit foundations for existing buildings.

KEY

AK-6

Page 18: Earthquake Hazard Maps & Liquefaction...Earthquake Hazard Maps & Liquefaction Includes activities on Ground-Shaking Amplification, Seismic Landslides, and Liquefaction What are earthquake-hazard

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This map is derived from Geographic Information Systems data developed and maintained by the Municipality of Anchorage ("MOA"). This map is not

the official representation of any of the information included and is made available to the public solely for informational purposes. This map may

be outdated, inaccurate and may omit important information. Do not rely on this information. The Municipality will not be liable for

losses arising from errors, inaccuracies or omissions in the map.

ZONE 2 - (Moderately-Low Ground Failure Susceptibility)

ZONE 3 - (Moderate Ground Failure Susceptibility)

ZONE 4 - (High Ground Failure Susceptibility)

ZONE 5 - (Very High Ground Failure Susceptibility)

ZONE 1 - (Lowest Ground Failure Susceptibility)

50 0.4 0.80.2

Miles

Map Prepared By: GIS Services

Data, Projects & Procurement DivisionInformation Technology Department

Municipality of Anchorage

December, 2006

Anchorage Bowl

Seismic

Chugach State Park

18

This seismic hazard map was downloaded from: www.muni.org/Departments/OCPD/Planning/Planning%20Maps/Anch_Bowl_Seismic_8x11.pdfA Siesmic Risk Assessment pamphlet is available from: www.muni.org/Departments/OCPD/Planning/Publications/Downtown%20Anchorage%20Seis-mic%20Risk%20Assessment/Downtown%20Anchorage%20Seismic%20Risk-Full%20Doc.pdf