slide © ubc-eosc 2001 the shaking earth - earthquakes your personal stake in earthquake science:...

slide © UBC-EOSC 2001

The Shaking Earth - Earthquakes

Your personal stake in earthquake science:

• Quakes cause the most misery in the shortest amount of time.

• BUT, with knowledge, we can mitigate their effects!

Understanding=> effective harm reduction & affordable

management.

Who needs to know? Law/policy makers, engineers, locals, etc … One result of a living, dynamicplanet …

Earth !


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


Outline for today:

• Nisqually - the most recent earthquake felt at UBC.

• Global distribution of earthquakes.

• Examples of effects on human society.

• Relation to plate tectonics.

• Cascadia - our regional context.

All reading assignments listed at http://www.eos.ubc.ca/courses/eosc114/P/EOSC114notes/EarthquakeNotes/EQOverview.html

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


Who felt the Nisqually ‘quake, Feb. 28, 2001?

• What did it feel like in Vancouver?

• What did it feel like in Olympia (S. Puget Sound)?

• Was it

– large?

– Significant?

– Costly? Lives? Dollars?

• Mag 6.8, ~ 40km deep,

near Olympia Washington.


Washington Capitol Bldg (Olympia)

http://maximus.ce.washington.edu/~nisqually/struc/buildings/olympia/wa_fed/img082.jpg

slide © UBC-EOSC 2001Highway 101

http://maximus.ce.washington.edu/~nisqually/geo/hwy101.html


How unique? (Western Canada)

One year of earthquakes:July, 2000 - July, 2001.

Approximately 1600 quakes.

From NRC (GSC), Pacific Geoscience Centre (PGC), Sydney BC

slide © UBC-EOSC 2001How unique? (SW BC)

http://www.pgc.nrcan.gc.ca/seismo/recent/eqmaps.html

Nisqually, Feb 28, 2001

One year of earthquakes:July, 2000 - July, 2001.

From NRC (GSC), Pacific Geoscience Centre (PGC), Sydney BC


How often (frequency)?

• PGC quotes around 1600 per year in BC => ~ 4.4 / day.

For GLOBAL frequency see Abbot 4th ed., table 3.3.


Where do earthquakes occur?

See also Abbott 4th ed, figs 2.6, 2.12, 2.13


Where do BIG ones occur?

Magnitude > 7.0 1975-2001

Note the pattern.

Implications for hazard assess-ment and earth-quake prediction will be discussed in a later lecture.


What impact on human history?

• Abbott discusses the Lisbon 1755 earthquake’s impact on global politics and economy.

• “Cradles” of civilization are often in earthquake zones.

• Local legends refer to somecatastrophic events.


August 17, 1999 (3:02 AM), Mw = 7.4 in the Kocaeli area, NW Turkey. Population = 1/3 of Turkey; 20 million, 1/2 Turkey’s industry. One of the most devastating earthquakes of the 20th century in terms of casualties & damage.

Current impact of big earthquakes: Turkey, 1999

Understanding still needs work!

Why did some buildings kill while others were nearly unaffected ?


Even moderate earthquakes can be devastating

Bam, Iran Dec. 26, 2003

Kobe, Japan 1995


Earthquake disasters in perspective:

• 40 Deadliest Disasters, 1970 - 2001. Mostly in 3rd world countries – Earthquakes and volcanoes 22

– Weather related 15

– Human causes 3

ItalyJapan

China

China

ChinaPakistan

Peru

China

Armenia

Iran

Abbott 4th ed., table 1.3


Your National Tax $$

• The economic return of NRC's earthquake program is ~$43 million per year, or 15 x the cost …

• Cost of the program ~ $2.9 million per year.

GSC Open File 3764 (1999) http://www.seismo.nrcan.gc.ca/hazards/OF3764/OF3764abs.html


Today’s outline …

• Nisqually - our most recent felt experience.

• Global distribution of earthquakes.

• Examples of effects on humanity all around the

globe.

• Relation to plate tectonics.

• Cascadia - our local context.

Arizona Tribune Newspapers, Mike Ritter


Recall where earthquakes occur …


Rigid pieces of crust moving on a sphere:


Rigid pieces of crust moving on a sphere:

http://pubs.usgs.gov/publications/text/Vigil.html

Sliding boundaries

Diverging boundaries

Converging boundaries, 2 types

(order)


Plate tectonics in action...

QuickTime™ and aVideo decompressorare needed to see this picture.

animation by Tanya Atwater, UC Santa Barbara

slide © UBC-EOSC 2001Plate speeds:

• Plates with subducting edges are fastest.• Continental (less dense) plates move more slowly.

Vancouver


Pacific Northwest …

Magnetic evidence for plates:

• Spreading centres are along

lines of symmetry.

• Subduction zone is along

the coast line.

• Continents have “chaotic”

magnetic signature.

• This region is called

“Cascadia”.

PacificPlate

Juan de Fuca

Subduction

Spreading Sliding

Magnetic stripes on seafloor: see Abbott, 4th ed., Figures 2.10 and 2.11


Cascadia and the Nisqually earthquake

Epicentre(nearest surface location)

Hypocentre or Focus(actual location at depth)


What’s driving it all?

• What are the internal energy sources?– Gravity pulls dense material down.

– Heat drives convection (hotter, less dense material rises).

• Results:– Lighter material floats on top (crust).

– Convection => motion => crust gets pushed around.

– At collision zones:• Older, cooler, denser material dives.

• Stiff slabs get pulled.

– Creating new crust => plates move apart. http://pubs.usgs.gov/publications/text/unanswered.html

• Internal energy sources


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

slide © ubc-eosc 2001 the shaking earth - earthquakes your personal stake in earthquake science:...

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