1. Marina District after Loma Prieta Earthquake, 1989
Photo: GSA, Explore Earthquakes CD-Rom

2. Damage to garages in Marina District, Loma Prieta EQ, 1989
Photo: GSA, Explore Earthquakes CD-Rom

3. House that slid off foundation during Loma Prieta EQ, 1989
Photo: GSA, Explore Earthquakes CD-Rom

4. Collapsed walls of house, Loma Prieta EQ, 1989
Photo: GSA, Explore Earthquakes CD-Rom

5. Collapse of 5 story tower, Loma Prieta EQ, 1989
Photo: GSA, Explore Earthquakes CD-Rom

6. Northridge Earthquake Damage

7. Collapse of Interstate 5, Northridge EQ, 1994
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8. Highway damaged during Northride EQ, 1994
Photo:
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9. Highway Damage, Northridge Earthquake, 1994
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10. Damaged Building, Northridge EQ, 1994
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11. Earthquake Destructiveness
Destructive earthquakes are even more common in Japan than in California
Japan is the best prepared nation to deal with earthquakes, with strong public education campaigns, building codes and warning systems
Despite this, more than 5600 people were killed in a mag 6.9 EQ in Kobe in 1995
Casualties and structure failure (50,000 buildings destroyed) occurred because of less stringent building codes that were in effect when most of the city was built and the proximity of the rupture to the city

12. How Earthquakes Cause Damage
Primary effects:
Faulting (breaks in ground surface)
Ground shaking (from seismic waves)
Secondary effects:
Landslides
Tsunamis
Fires

13. Faulting and Shaking
Ground surface can subside or uplift during faulting
Ground accelerations near the epicenter can exceed the acceleration of gravity, so objects lying on the surface can be thrown into the air

14. Faulting and Shaking
Seismic waves can shake structures so hard that they collapse, which is the leading cause of casualties and economic damage
Examples:
Tangshan, China 1976: >240,000 killed
Spitak, Armenia 1988: 25,000 killed
Izmit, Turkey 1999: 15,600 killed
Etc…

15. Landslides and Other Ground Failures
Landslides can bury towns
Ex: debris flow in China’s Kansu Province, 1920, covered >100 km2, 200,000 killed
Water saturated soils can behave like a liquid – called liquefaction – and flow away, taking buildings, bridges, etc along with it
Ex: cause of massive building collapse in Mexico City EQ: Mexico City built on unstable soils of ancient lakebed

16. Liquefaction in Niigata, 1964
Photo:
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17. Tsunamis
Destructive sea wave triggered by earthquake beneath the ocean
NOT called tidal wave – this term is incorrect, has nothing to do with tides
Deadliest and most destructive hazard associated with largest earthquakes – megathrust quakes that occur in subduction zones

18. Tsunamis
Megathrust ruptures can push the seafloor upward by as much as 10 m, displacing the overlying ocean water
Resulting wave travels at speeds of up to 800 km/hr, as fast as a jetliner
They are hardly noticeable in deep ocean, but waves slow down and pile up when they reach shallow coastal waters
Resulting wave can be tens of meters tall

19. Tsunamis Most common in Pacific Ocean, why?
Ring of Fire – subduction zones ring the Pacific
Examples:
1964 Alaska EQ caused tsunamis that hit thousands of kilometers from epicenter. At one location, near Valdez, AK, the tsunami ran up a mountainside to a height of 67 m (that’s 220 feet)!
2004 Indian Ocean EQ caused tsunamis that killed 300,000 people in several countries

20. 1946 Tsunami Hilo, Hawaii. Caused by earthquake in Aleutian Islands
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21. Damage from 1946 tsunami, Hilo, Hawaii
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22. Aftermath of 1960 tsunami at Hilo, Hawaii; caused by earthquake in Chile
Photo:
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23. Damage to hotel from Indian Ocean tsunami, 2004
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24. Fires
Are ignited by ruptured gas lines or downed electrical power lines
Damage to water mains can making fighting them impossible, as happened in the 1906 San Francisco EQ

25. Reducing Earthquake Risk
Seismic hazard – describes the intensity of seismic shaking and ground disruption that can be expected
Seismic risk – describes the damage that can be expected for a specific region
Risk depends on the seismic hazard, population, and number of built structures

26. Reducing Earthquake Risk
California leads the nation in seismic risk at 75% of the national total, with Los Angeles county accounting for 25%
But 46 million people are at risk outside of California, including: Hilo, Honolulu, Anchorage, Seattle, Tacoma, Portland, Salt Lake City, Reno, Las Vegas, Albuquerque, Charleston, Memphis, Atlanta, St. Louis, New York, Boston & Philadelphia

27. United States seismic hazard map
Photo:

28. Land Use Policies
Exposure of built structures to earthquake risk can be reduced by policies that restrict land use
It is unwise to erect buildings on known active faults, as was done in residential areas of San Francisco.
California law now restricts construction across active faults.
Real estate agents are required to disclose information about houses built on a fault

29. Earthquake Engineering
Risk from seismic shaking can be reduced by good engineering and construction
Building codes specify the forces a structure must be able to withstand from a seismic hazard
U.S. building codes have been largely successful in preventing loss of life during earthquakes
Ex: from 1983 to 2004, 131 people died in nine severe earthquakes in the western U.S., whereas >460,000 people were killed by earthquakes worldwide

30. Warning Systems
When an earthquake occurs, automated seismic systems can send warnings tens of seconds before the arrival of destructive seismic waves
Tsunamis travel 10 times slower than seismic waves, so distant shorelines can be given up to hours of warning time
Unfortunately, no system had been installed in the Indian Ocean during the 2004 quake

31. Can Earthquakes be Predicted?
Prediction means specifying time, location and size
Information from plate tectonics and geologic mapping of fault systems can allow geologists to forecast which faults are likely to produce earthquakes over the long term
To specify precisely when a particular fault will rupture is very difficult

32. Long-Term Forecasting
The longer the time since the last big EQ, the sooner the next one will be
Recurrence interval – the average time between large earthquakes.
Determined by strain rate – how long it takes for a fault to build up enough strain that rock strength is exceeded

33. Short-Term Prediction
There have been a few successful short-term predictions
Ex: in 1975, an EQ was predicted only hours before occurring near Haicheng, China
Seismologists used precursors of swarms of tiny earthquakes to make prediction
The next year, however, an unpredicted quake struck the Chinese city of Tangshan, killing more than 240,000
No reliable method of short-term prediction has been found