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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.php7/28/2019 L11 - Earthquake Hazard - Steve Crane
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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/7/28/2019 L11 - Earthquake Hazard - Steve Crane
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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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Example: Mexico City, 1985
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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Example: Mexico City, 1985
Spectral acceleration for UNAM (Rock) and SCT(Clay)
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Example: Mexico City, 1985
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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Local Site Amplification
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
Local Site Amplification
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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
Canadian National Seismograph Network
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.php7/28/2019 L11 - Earthquake Hazard - Steve Crane
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Canadian National Seismograph Network
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/