PowerPoint slides on the ways in which earthquakes damage structures

1. This work is supported by the National Science Foundation’s
Transforming Undergraduate Education in STEM program within the
Directorate for Education and Human Resources (DUE-1245025). Questions, contact education-AT-unavco.org
IMAGING ACTIVE TECTONICS UNIT 1
HOW EARTHQUAKES DAMAGE STRUCTURES

2. OUTLINE
• How earthquakes cause damage
• How might that damage affect society?
• What do we need to know to prepare?

3. DAMAGE!
In what ways do earthquakes cause damage
to structures, and why?
Think on your own for a minute, and then
confer with your neighbor for a minute, and
come up with a list.

4. DAMAGE!
strain!
shaking
• resonance
• toppling
• swaying
liquefaction
• differential movement
• sinking
landsliding
• differential movement
• burial
fault offset
• differential movement
secondary effects
• fire
• flooding

5. NEWTON’S SECOND LAW AND INERTIA
F = m a
force = mass x acceleration
Inertial Response
Building at
Rest
Ground Motion

6. NEWTON’S SECOND LAW AND INERTIA
D’Alembert’s principle: the inertial force on a mass
resisting acceleration is of equal magnitude and in the
opposite direction.
Inertial Response
Building at
Rest
Ground Motion

7. YIELD STRAIN
Inertial forces cause shear strains in a structure and its components. If
any element exceeds its yield strain, it will be permanently damaged.
Lateral
load
Yield Point
Ductile
Brittle
Deflection
Elastic
Range

8. TOPPLING AND ROTATION
One response of a structure to lateral inertial forces is
to rotate like an inverted pendulum. If it is not secured
at its base, it may topple.
Free-standing

9. TOPPLING AND ROTATION
On the other hand, if it is secured at its base, it must
absorb the inertial force internally, possibly leading to
yielding at its base.
Free-standing Fixed-base

10. SWAYING AND RESONANCE
Structures have their own natural frequencies, related
to their dimensions and stiffness. If they are shaken at
those frequencies, they will resonate.
Download video from:
http://www.iris.edu/hq/programs/%20e
ducation_and_outreach/videos#P

11. SITE AMPLIFICATION
Seismic waves traveling from stiff rock to softer
material (e.g. from basement to a sedimentary basin)
typically experience an increase in shaking amplitude.
Why?

12. SITE AMPLIFICATION
Conservation of kinetic energy requires that amplitude
of shaking increase when waves travel into less stiff
materials. This can strongly affect the likelihood of
building damage.
small x large = large x small
amplitude stiffness amplitude stiffness

13. LIQUEFACTION
Water saturated
Loose sediments
Sand injected
into overlying
area upon
shaking

14. LIQUEFACTION

15. LIQUEFACTION
Above: Christchurch, New Zealand
sand boils (2011 earthquake)
Right: Christchurch, New Zealand
road affected by liquefaction

16. BUILDING DAMAGE FROM SHAKING

17. LANDSLIDES
Above: Wenchuan, China, 2008
Right: El Salvador, 2001

18. FAULT OFFSET
Above: Horizontal offset from 1906
San Francisco earthquake (Marin
County)
Right: Vertical offset from 1999
Taiwan earthquake

19. TRANSPORTATION CORRIDOR DAMAGE
Above: South Napa, CA earthquake 2014
Right: Northridge, CA earthquake 1994

20. SECONDARY HAZARDS

21. SAN FRANCISCO, 1906
The worst damage in San Francisco was caused
by the fire following the earthquake, not the
earthquake itself. (Why?)

23. Port of Seattle
Major highway

24. EARTHQUAKE PROBLEMS!
In what ways might earthquake damage to
structures (buildings and infrastructure)
affect society?
Think on your own for a minute, and then
confer with your neighbor for a minute, and
come up with a list.

25. RISK VS HAZARD
Informally, people use these terms interchangeably,
but in the natural disasters field, they have specific,
different definitions.
Hazard refers to the probability of a particular
disaster–e.g. earthquake hazard = the
likelihood of a given size of earthquake
occurring.
Risk refers to the likely implications of such a
disaster, and usually is quantified in dollars–e.g.
uninsured earthquake risk in LA is ~ $100 billion.

26. PREPARING FOR EARTHQUAKE HAZARDS
What information might we want to have in
order to characterize and prepare for future
earthquake risk and hazard?
Think on your own for a minute, and then
confer with your neighbor for a minute, and
come up with a list.