slide © ubc-eosc 2001 the shaking earth: mitigation & prediction

slide © UBC-EOSC 2001

The Shaking Earth: mitigation & prediction


Outline for “The Shaking Earth”

NB: Readings & lectures are complementary - some unique coverage in both.

We investigate five aspects of earthquake science:Effects and global distribution

Local context, global distribution, effects, plate tectonics.Earthquake sources

Forces, types of faults, slip during earthquakes.Seismic waves

Ground motion, wave types, wave propagation, using waves to study

earthquakes

Human impact and engineeringWhat kills?, magnitude vs. intensity, earthquake-resistant structures.

Mitigation and Predictionpredicting occurrence and effects, minimizing damage


Mitigation: Preparedness

UBC information– UBC Health, safety, and environment:

• http://www.hse.ubc.ca/innerContentFrame.php?

type=pubsAndProcs&ln=11-Earthquake.PDF

Vancouver info:

http://www.city.vancouver.bc.ca/fire/emerg_prep.html

BC info:

http://www.pep.bc.ca/

Canada info:

http://www.epc-pcc.gc.ca/ http://www.seismo.nrcan.gc.ca/hazards


Mitigation: BC government

• Risk Management Branch of Ministry of Finance

• The Seismic Mitigation Program:– $133 million for fiscal years 1999 - 2003

– structural and nonstructural seismic upgrade of

• schools,

• post-secondary facilities,

• hospitals

• post-disaster facilities

Natural Resources Canada - seismic hazard reports: maximum acceleration and velocity (for various probabilities); basis for 2005 National Building Code of Canada


Mitigation: Building design Abbott 4th ed, pgs 81 - 83

Damping:• Absorb energy caused by

moving ground.

From University of Bristol, Department of Civil Engineering Earthquake Engineering.http://www.cen.bris.ac.uk/students/eqteach97/welcome.htm

Isolation: • Let ground move under the

building


Mitigation: Building design (shear walls)

QuickTime™ and aDV/DVCPRO - NTSC decompressorare needed to see this picture.


Mitigation: construction practices

• Cosmetic facing can be

dangerous

• Concrete must be

reinforced …

• But it must be

done properly!


Mitigation: a local example

Seymour Falls Dam Seismic Upgrade:

• Upgrading an earth-filled dam (2003-2008):

– The structure is strong, but would fail in a major

earthquake by liquefaction of the soil foundation.

• A new foundation will be made by blasting &

dropping large weights (dynamic compaction).

– “Blast densification” is new in SW BC.

– Explosions cause soil layers to settle and become

dense so they won't flow when the BIG ONE comes. http://www.gvrd.bc.ca/water/pdfs/seismic.pdfhttp://www.gvrd.bc.ca/water/current-projects.htm


Earthquake engineering at UBC

• UBC Department of Civil Engineering

• Earthquake simulator facility for seismic research and qualification testing.

http://www.civil.ubc.ca/home/eq_lab/

Shear-wall test on seismic simulation table.

Scale model of a building on the seismic simulation table.

Research at UBC inCivil Engineering


Prediction

Predict ...1. Where earthquakes will occur?2. When an event will occur?3. What effects if an event occurs?4. Specifics about Cascadia?

“Since my first attachment to seismology, I

have had a horror of predictions and of

predictors. Journalists and the general

public rush to any suggestion of earthquake

prediction like hogs toward a full trough.”

Charles Richter, Bulletin of the Seismological Society of America, 1977.


Prediction: Geologic faults are complicated.

• The San Andreas is the most studied fault system ever.

• “Seismic gaps” are regions “due” for an earthquake.

BUT …most fault systems are poorly studied.

San Francisco

0km Distance 350km

Loma PrietaDots show 20 yrs of earthquakes

Loma Prieta earthquakes: red dotsseismic gap


Prediction - San Andreas

The San Andreas is the most studied fault system ever.

But it is a complex system of faults, especially around Los Angeles.


“Prediction” using stress patterns

• Recall we showed stress changes at the 1999 Izmit earthquake:

http://quake.wr.usgs.gov/~ross/


• Red: Stress jumps up after M=7.3 ‘quake (Landers, CA, 1992).

• Small quakes, plus M=6.5 (Big Bear), in 3 hrs following.

• Majority of quakes in the next 7 years are in stressed zones.

Earthquakes causing more earthquakes

http://quake.wr.usgs.gov/~ross/


Prediction: When … ?

• When will a “seismic gap” be filled?Break a stick - exact moment can not be

predicted

• BUT …

– Parkfield experiment based on “prediction”.

– Chinese “predicted” successfully once, but failed terribly in 1976 (Tangshan

- 250,000 fatalities!).

– Japan focussed work in early 1990’s on prediction in Tokyo region, then

Kobe was struck catastrophically.

2004


Prediction: Probability of a quake

• In spite of progress, prevention of catastrophic effects is often considered more cost-effective than “prediction”.

1. Each fault segment has an average time between events. Probability remains constant.2. If stress increases gradually, then the chance of a damaging shock grows as time passes.

3. Effects of stress changes caused by nearby earthquakes may cause probabilities of a shock to jump.


Prediction: Effects?

• We can predict how the ground will move.

East-west & north-south ground motion for two Parkfield earthquakes, recorded at Berkeley, CA. http://quake.wr.usgs.gov/research/parkfield/berkeleyrecords.html

• Therefore we can design buildings to survive, and develop emergency response procedures.


Prediction: Cascadia?

• Where? When? How large?

• Recurrence relation gives one way of estimating how often `quakes might occur.

• Gutenberg / Richter curve.

Queen Charlotte Fault

Cascadia

Earthquake magnitude, M

Ear

thq

uak

es p

er y

ear

> M

Queen C

harlo

tteFau

ltDATA:- Many ‘quakes with M < 6- 4 ‘quakes with M ~ 7.5-8- 1 ‘quake M ~ 8-9 (1700)


Prediction: Cascadia?

Evidence:• Mega-quake,

9:00PM, January 26, 1700

– Tsunami in Japan on January 27.• Mega-quakes every

400-600 years– tree rings/drownedforests, ocean landslides• Real-time tectonic

deformation (GPS)

Conclusion? A Megathrust earthquake in Cascadia is likely. Therefore we must prepare to deal with it.


QuickTime™ and aGIF decompressorare needed to see this picture.

"The water also went into the pine trees of Ego. The receding water went out very fast, like a big river. It came in about seven times before 10 a.m. of that day and gradually lost its power…Because the way the tide came in was so unusual, and was in fact unheard of, I advised the villagers to escape to Miho Shrine…It is said that when an earthquake happens, something like large swells result, but there was no earthquake in either the village or nearby."

Tsunami from a Cascadia earthquake: 1700

-account from the head of Miho village, near Tokyo

slide © UBC-EOSC 2001Drowned forests - evidence of Cascadia

mega-earthquake

Oregon coast

wood fragments sandwiched between sand layers where land surface dropped suddenly and killed a mature forest

photos by Steve Carlson

slide © UBC-EOSC 2001As Vancouver Island is squashed, stresses

are building on the subduction zone...

Henton et al., 2001


Prediction recap …

1. Where will earthquakes occur?

3 aspects of prediction, & some complications for each.

2. Exactly When will an event occur?> 3 ways to estimate probability - include evolving stress patterns.

> Reliable, detailed records exist for only ~100yrs.

3. What effects can be anticipated if an event occurs?> Knowing ground motion permits better buildings.

What about Cascadia?- Large quakes have occurred.- Recurrence rate of large quakes is ~400-600 years.- Plate dynamics is being studied.- Preparation and hazard mitigation can be done.

> Faults, but geometry and physics is complicated.


That concludes Earthquakes

• Earthquakes kill thousands world-wide every year.

• They are a factor in S.W. BC.

• Understanding causes /effects /patterns is pre-requisite

for

– Minimizing tragedy

– Reducing costs


Active Research in Earthquake Science

Examples of current research topics:– Earth’s internal processes, chemistry & structures.– Physics of tectonic plate behaviour.– Using seismic waves to image Earth’s interior.– Earthquake-earthquake & earthquake-volcano interactions.– Hazard mitigation & management.

At UBC’s EOS Department:– Global structure, Crustal structure (Cascadia).– Fault physics, earthquake stresses, interaction, prediction.– Clowes, Hearn, Bostock, Herrmann, Ellis, and students.


Outline for “The Shaking Earth”

We investigate five aspects of earthquake science:Effects and global distribution

Local context, global distribution, effects, plate tectonics.Earthquake sources

Forces, types of faults, slip during earthquakes.Seismic waves

Ground motion, wave types, wave propagation, using waves to study

earthquakes

Human impact and engineeringWhat kills?, magnitude vs. intensity, earthquake-resistant structures.

Mitigation and Predictionpredicting occurrence and effects, minimizing damage


This is just the beginning!

Our Planet - understanding is the key to survival.

slide © ubc-eosc 2001 the shaking earth: mitigation & prediction

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