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 I MAGING A CTIVE T ECTONICS U NIT 1 H OW EARTHQUAKES DAMAGE STRUCTURES

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

3. D AMAGE ! 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. D AMAGE ! strain! shaking resonance toppling swaying liquefaction differential movement sinking landsliding differential movement burial fault offset differential movement secondary effects fire flooding

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

6. N EWTON ’ 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. Y IELD 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. T OPPLING 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. T OPPLING 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. S WAYING 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. S ITE 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. S ITE 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

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

14. L IQUEFACTION

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

16. B UILDING DAMAGE FROM SHAKING

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

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

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

20. S ECONDARY HAZARDS

21. S AN F RANCISCO, 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. E ARTHQUAKE 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. R ISK 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. P REPARING 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.