L11 - Earthquake Hazard - Steve Crane

7/28/2019 L11 - Earthquake Hazard - Steve Crane

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Earthquake Hazard

Presented by: Stephen Crane, M.Sc.

Ph.D. Candidate Earth Science


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Lecture Outline

Earthquake intensity

Earthquake damage

Mitigation against earthquake hazards


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Review

Earthquake Locations: most (but not all) occur

along plate boundaries

Seismic waves: body and surface waves

Earthquake Size: measured with magnitudescales.


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Earthquake Intensity

Intensity: Qualitative description at a location,

as evidenced by observed damage and human

reactions

vs.

Magnitude: Quantitative measure of the size

and strength of an earthquake


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Qualitative

Uses descriptions from those affected. Can infer intensity from pastevents with no recordings

1906 San Francisco earthquake, CA; eyewitness account

" Of a sudden we had found ourselves staggering and reeling. It wasas if the earth was slipping gently from under our feet. Then camethe sickening swaying of the earth that threw us flat upon our faces.We struggled in the street. We could not get on our feet. Then itseemed as though my head were split with the roar that crashed

into my ears. Big buildings were crumbling as one might crush abiscuit in one's hand. "

Source: http://www.eyewitnesshistory.com/


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Intensity Scales

Intensity is measured using a scale: oftenranging from not felt to total damage

Several scales used worldwide:

Most english speaking countries: modifiedMercalli intensity (MMI)

Japan: Japanese Meterological Agency (JMA) Central and Eastern Europe: Medvedev-

Spoonheuer-Karnik (MSK)


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Modified Mercalli Intensity Scale

Originally developed by Mercalli (Italian

Sesimologist)

Modified by others, including C. Ricter

(American Seismologist), to correspond to

California conditions

Ranges from I XII


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Isoseismal Maps

Contour map of earthquake intensity

Based on damage observed and reports

Did you feel it?http://www.earthquakescanada.nrcan.gc.ca/dyfi-lavr/known-connu-eng.php

Asks for when, where and how intense was it?
http://www.earthquakescanada.nrcan.gc.ca/dyfi-lavr/known-connu-eng.phphttp://www.earthquakescanada.nrcan.gc.ca/dyfi-lavr/known-connu-eng.phphttp://www.earthquakescanada.nrcan.gc.ca/dyfi-lavr/known-connu-eng.phphttp://www.earthquakescanada.nrcan.gc.ca/dyfi-lavr/known-connu-eng.phphttp://www.earthquakescanada.nrcan.gc.ca/dyfi-lavr/known-connu-eng.phphttp://www.earthquakescanada.nrcan.gc.ca/dyfi-lavr/known-connu-eng.phphttp://www.earthquakescanada.nrcan.gc.ca/dyfi-lavr/known-connu-eng.phphttp://www.earthquakescanada.nrcan.gc.ca/dyfi-lavr/known-connu-eng.php


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June, 2010 Val-de-Bois Earthquake

Source:S

tep

henHa

lchu

k,G

SC

Pre

liminaryreport

,s

hownw

ith

permission


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1935 Temiscaming earthquake (M6.2)

Source:

M.

Lamontagne

,NR

Can

.

Shownwit

hpermission

.


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Other Intensity Maps

Isoseismal maps are good to use but:

They take a while to create

Only as good as the records and reports allow

Would like something almost real time, i.e.

ShakeMaps:

Created moments after an earthquake, and updated

Use recorded values to determine intensity

USGS has a ShakeMap generator
http://earthquake.usgs.gov/http://earthquake.usgs.gov/research/shakemap/http://earthquake.usgs.gov/research/shakemap/http://earthquake.usgs.gov/research/shakemap/http://earthquake.usgs.gov/research/shakemap/http://earthquake.usgs.gov/


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Source:U

SGSEart

hqua

kes

.

Shownwithpermission

.


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Source:

USGSEart

hqua

kes

.

Shownwit

hpermission

.


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Earthquake Damage


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Earthquake Damage

Factors include:

Earthquake parameters: magnitude, duration of

shaking, epicenter location, depth, etc.

Aftershocks

Site conditions, ex. rock vs soil

Building style and materials


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Magnitude

Larger magnitude = higher intensity


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Duration of Shaking

Larger magnitude = longer time of strong

shaking

Note: there are several magnitude scales are based on the duration


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Epicenter Location

Close to populated areas = not good

Shallower earthquakes produce strongershaking

Hypocenter Depth


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Aftershocks

Occur often gradually decreasing over time

after a main shock

Can be almost as strong as the main shock

Example: 2002, November 3rd

M7.9 DenaliEarthquake (Alaska)


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Sourc

e:

USGSEart

hquake

s.

Shownwit

hpermission.


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Distance from Epicenter

Waves attenuate more with distance travelled

Can depend on the region: i.e. western N. A.attenuates faster than eastern N. A.


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Source: Earthquakes Canada


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Ref.: Abbott, P.L. 2004. Natural Disasters.

4th Edition. Fig. 5.16. Shown with permission.


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Local Site Conditions

Where you are can strongly influence the

intensity of shaking you feel

Top 0-30m can have a large impact on the

ground motion

Local site amplification

Liquefaction

Landslides


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Example: Mexico City, 1985

Magnitude 8.1

Subduction zone earthquake

8,000 lives lost Severity of damage related to near-surface

conditions

Mexico City built over drained Lake Texcoco

Ground motion of soft lake sediments amplified by

surface waves


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Re

f.:

Abbott,

P.L.

2004

.Natura

lD

isasters

.

4th

Edition

.F

ig.

4.6.

Shownwith

permission

.

Rock

~370km

Soft lake

sediments

~400km


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Spectral acceleration for UNAM (Rock) and SCT(Clay)


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The damage in Mexico City was in a large partdue to COINCIDENCE between the dominantperiod of the ground shaking and the natural

period of vibration of these high-risestructures.

Most severe damage to almost 400 buildingsbetween 7 and 18 storeys in height. (EEFIT,1986)


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Local site effects are built into the NBCC

Building design for seismic loading is

dependent upon:

Location

NEHRP site classification (we will discuss this

shortly)

Local Site Amplification


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Rocks and Soils have a different response

frequency content

amplitude of ground motions

0-30m is a good indicator of site response

(measure Vs30)


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Local site amplification effects include:

Broadband amplification

Resonance amplification

Focusing (defocusing) of seismic waves

Surface wave generation at basin edges



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Broadband Amplification

Seismic waves increase amplitude travelling

through softer materials

Source:

J.Hunter,GSC


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Resonance Amplification

Seismic waves get trapped in an acoustic

medium

Certain frequencies have stronger amplifications

Source:

J.Hunter,GSC


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Focusing (Defocusing)

Waves combine or disperse depending on

bedrock topography

Source:

J.Hunter,GSC


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Surface Wave Generation

Basin edges are known to generate surface

waves

Seismic waves are amplified and periods are longer

Source:

J.Hunter,GSC


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Liquefaction

Liquefaction: phenomenon in which the

strength of soil is reduced by rapid and

violent shaking

Occurs in saturated soils in which the space

between particles is filled with water

Liquefied soil behaves like a liquid

Does not have the strength to support a load


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1964 Niigata earthquake, Japan

Source: Steinbrugge Collection, EERC


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Landslides

Soils or clays along a slope fail and shift

downwards

i.e. Force of gravity overcomes the cohesive

strength of the soil


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Lemieux, Ontario

Settled around 1850 as a milling and farming

community

Purchased by South Nation River Conservation

Authority and Ministry of Natural Resources

for Ontario in 1989

All homes were moved or destroyed by 1991


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Lemieux Landslide, 1993

Caused by heavy rainfall

Covered 17 hectares

Crater dimensions = 680m long by 320m wide by 18m deep

2.5-3.5 million cubic meters of debris


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Landslides

Other landslides in the region are thought to

be caused from earthquakes

15 landslides dated around 4550 years ago

Large deformation of soil and sand areasdated at 7060 years ago


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Building Style and Materials

Earthquakes dont kill, buildings do.

Very few people have died as a direct result of anearthquake. Most deaths occur from secondary

disasters; i.e. tsunami, fire, building collapse, etc.

b


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Comparison between San Francisco

and MessinaSan Francisco Messina

California Sicily

United States Italy

Date 18 April 1906 28 December 1908

Time 05:13 AM 05:23 AM

Magnitude 8.25 7.5

Associated disasters Tsunami NO NOFires Burning for 3 days Few small fires

Casualities Lost lives 700 83000

Survival rate 99.8% 45.0%

Structures Wood Masonry

In Messina, houses were predominantly masonry, withmassive stone floors and brick-tile roofs supported by

timber set into niches in granite walls"

Example from "Perils of a restless planet"


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Building Response

Different building materials behave differentlywhen subjected to external deformationforces

The same material can behave differentlydepending on the type of externaldeformation forces

Tension

Compression

Shear


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Types of Stresses

Shear

Tension Compression


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Elastic Limit

Materials behave elastically below this limit

(i.e. Return to original shape)

Above this limit, two possiblities:

Abrupt failure; stone, brick

Plastic deformation; wood, steel


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Failure

Elastic

behavior

Elastic limit

Deformationforcesac

tingon

thesurfa

ceofabody

Deformation

Plastic

behavior

Failure

Messina: structures were hard; failed at elastic limit

San Francisco: structures were soft; failed after plastic

behavior


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Building Response

Resonance amplification also affects buildings

Soft sediments

(f1Hz)

Bungalow (10 Hz) Vulnerable

Two-storey building (5 Hz)

High-rise building (1 Hz) Vulnerable

Near-surface geology

Buildings

Natural frequency


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Earthquake Damage

Which type of seismic wave is most damaging

to structures?

P-waves (compression, tension)

S-waves (shear)

Surface waves (tension, compression and shear)


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S-waves!

Shearing motion is often most damaging

S-waves tend to be the strongest waves close to theepicenter

Tension, compression already accounted for in buildingdesign (gravity)

Surface waves take some distance to fully develop (notas strong near source) However these can be stronger away from the source


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Mitigation against Seismic

Hazards


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Steps

1. Classify Seismic Hazard vs. Risk

2. Identify high/low risk areas

3. Determine likelihood of a certain level/type

of seismic loading

4. Mitigate the hazard as best as possible!


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Hazard vs. Risk

Seismic Hazard: shaking irrespective of

consequence

Risk = Hazard * Vulnerability

Vulnerability: likelihood that a community willsuffer injuries, deaths or property damage

from a hazardous event


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Seismic Hazard

Civilisation exists by geological consent,

subject to change without prior notice.William Durant, historian

Seismic Hazard: the possibility of that consent

being withdrawn


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Seismic Hazard

Can be found either:

Deterministically: maximum level of shaking

possible

Probabilistically: likelihood of above a certain level

of shaking over a specified time frame


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Seismic Hazard

What do we need to know?

Seismic sources in the area (historical seismicity,

paleoseismic studies)

Distance to these sources

Types (or sizes) of earthquakes


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Seismicity

Historical Seismicity: Earthquakes often occur where they have in the

past

Plate tectonics:

Earthquakes often occur along plate boundaries

Paleoseismic studies:

has a young fault (


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2010 NBCC Seismic Hazard Map of Canada


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2010 NBCC Seismic Hazard Map of Canada

Source:

Ear

thqua

kesCana

da,

shownwith

permission

Vulnerability Population distribution


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Vulnerability = Population distribution

Sou

rce:

Eart

hqua

kesCana

da

Seismic Risk


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Seismic Risk

Sou

rce:

Eart

hqua

kesCana

da


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Sample of Risk Calculations

City Hazard Exposure Risk

Baffin Island High Low Low

Vancouver High High High

Toronto Low High Moderate


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Risk by Canadian City


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Now we know the high risk areas

and the regional hazards, how do we

mitigate these hazards?

Low Risk areas: monitor events and indicateareas of possible damage

High Risk areas: design and build accordingto specific hazards


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Monitoring

Canadian National Seismograph Network

Network of 160 seismographs

Data telemetered to Ottawa

Analysis in near real-time

http://www.earthquakescanada.nrcan.gc.ca/stndon/CNSN-RNSC/stnbook-cahierstn/index-eng.phphttp://www.earthquakescanada.nrcan.gc.ca/stndon/CNSN-RNSC/stnbook-cahierstn/index-eng.php


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3-component

Broadband

3-component

High Broadband

1-component

Extremely Short Period

1-component

Short Period

Earthquakes Canada:


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Earthquakes Canada:

Early Warning System

"Autoloc" software Automatic event detection and location

Rapid earthquake alert service (AENEAS)

Issues alerts to railways, dam owners, nuclearpower plants

Usually within 8 minutes

2-3 valid notifications/year

1-2 false alarms/year

Rapid alerts help ensure the right actions aretaken promptly

Al t t il

Source: J. Adams, Earthquakes Canada


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Earthquake Report Rapport d'un tremblement de terre

Date : 2000/01/01 Time/Heure : 11:22:56 UT

Epicenter : 47.11 -78.74 Region : east/est

Magnitude : 5.3 Richter Status : Q018/OTT

104 KM NE OF NORTH BAY, ONT.

--------------------------------------------------------------------------------

Action

PROCEED AT RESTRICTED SPEED... LES TRAINS ET LES LOCOMOTIVES DEVRONT

until inspections have been OBLIGATOIREMENT CONTINUER LEUR AVANCE

completed and appropriate speeds VITESSE DE MARCHE VUE...

established by proper authority jusqu' ce que les inspections soient

termines et que l'autorit comptente ait dfini les vitesses particulires

respecter.

Line ( Station to/ Station ) From/de To/

Mile/Mille Mile/Mille

ALEXANDRIA (DE BEAUJEU to/ OTTAWA) 6.9 76.5

BALA (ZEPHYR to/ CAPREOL) 44.6 276.1

BEACHBURG (OTTAWA to/ FEDERAL) 0.0 6.0

CHAPAIS (BARRAUTE to/ CHAPAIS) 0.0 170.5

MATAGAMI (FRANQUET to/ MATAGAMI) 0.0 61.1 NEWMARKET (BRADFORD to/ YELLEK) 41.5 233.4

RUEL (CAPREOL to/ OATLAND) 0.0 176.4

ST MAURICE (PARENT to/ SENNETERRE) 118.9 257.2

TASCHEREAU (SENNETERRE to/ LA SARRE) 0.0 97.3

VAL D"OR (SENNETERRE to/ NORANDA) 0.0 101.2

WALKLEY LINE (HAWTHORNE to/ WASS) 0.0 5.8

--------------------------------------------------------------------------------

ACTION: CONFIRM RECEIPT OF THIS MESSAGE TO: [email protected]

Alert to railways

Proceed at

restricted speed

Track

segmentsaffected


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High Risk Areas

Specify level of hazard at that location Seismic hazard map of Canada is insufficient for this scale

Geotechnical evaluation of each site

= costly, not very time efficient

Microzonation of high risk regions

Use simple measurement to classify specific locations

NEHRP site classification

National Earthquake Hazard


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National Earthquake Hazard

Reduction Program (NEHRP)

Site Class Generic Description Range of Vs30 (m/s)

A Hard Rock >1500

B Rock 760 - 1500

C Very dense soil and soft rock 360 - 760

D Stiff soil 180 - 360

E Soil profile with soft clay < 180

F Site-specific geotechnical investigation

required (sensitive and liquefiable soil)

Vs30 site classification for seismic site response as defined by NEHRP (1994) and

adapted by the 2005 National Building Code of Canada

Microzonation of Ottawa


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Microzonation of Ottawa

Source: Dr. Motazedian, Carleton University, shown with permission


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Microzonation

Other high risk areas are microzoned as well;

Examples are Vancouver, Montreal

Helps to specify expected ground shaking in a

highly variable region

Map does not include site class F locations!


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Mitigation: Buildings

Avoid matching natural frequency of building

and natural frequency of the site

Design to be able to withstand certain levels

of seismic loading (minimum levels in NBCC)

Fundamental Period Map


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Fundamental Period Map

Avoid Building High-Rises Here

f


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National Building Code of Canada

Includes a uniform hazard spectrum which

buildings must be designed to withstand

Different for each city

Amplification factors for the different site classes

h


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Current Research

Modelling basin effects

3D vs 1D amplification

Soil strength and amplification

Large scale velocity mapping

ff


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Basin Effects

Can see several subsurface basins from

microzonation and fundamental period maps

Currently have 3 soil/rock seismometer pairs

in these basins

Objective: separate 1-D amplification from 3-D

amplification


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R f


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References

Abbott, P.L. 2004. Natural disasters. McGraw Hill.4th Edition.Kramer, S.L. 1996. Geotechnical earthquake

engineering. Prentice Hall.Zebrowski, E. 1997. Perils of a restless planet.

Cambridge University Press.

Interesting websites:

Earthquakes Canada

earthquakescanada.nrcan.gc.ca/index_e.phpUSGS Earthquakes

http://earthquake.usgs.gov/earthquakes/

Documents

L11 - Earthquake Hazard - Steve Crane