1. Earthquakes
Source: NPS
Source: USGS

2. Seismic Hazard
Source: USGS

3. California Tectonics: Present
Source: USGS

4. California Tectonics: Past

5. The San Andreas fault system is a relatively new geologic feature in the Bay Area; only forming within the last 28 million years. Older rocks in the area formed when the tectonic plate underlying the Pacific Ocean plunged under the North American Plate at a subduction boundary. The unusual rocks of the world-famous Franciscan Complex, named at San Francisco and underlying the Presidio, formed at this plate boundary. As the Pacific Ocean crust was thrust under the North American Plate, the Franciscan Complex formed from oceanic rocks that were scraped off of the subducting plate and churned into continental sediments derived from the North American Plate.

6. What Is An Earthquake? _______________________________________________

7. Types of Earthquake Waves
Surface waves
Complex motion
_________________________________
Body waves
1. Primary (P) waves
Push-pull (__________________) motion
Travel through solids, liquids, and gases
___________________of all earthquake waves
2. Secondary (S) waves
"Shake" motion
Travel only through _____________
____________________ than P waves

8. Seismic Waves

9. A seismogram records ________________vs. _________

10. Locating an ____________ from 3 seismograph stations
Measure the difference in arrival of ____________ waves.

11. Step 2 of locating the epicenter
2. Use a graph to determine the ______________ from the monitoring station to the epicenter.

12. Steps 3, 4 & 5 of Locating the Epicenter
Draw a circle, centered around the monitoring station with a radius _________ to the distance from the epicenter.
Repeat two more times.
5. The point where all three circles intersect is the location of the ______________.

13. Measuring The Size of An Earthquake
______________ – determined by effects on people, structures, and the environment
_______________ – measures energy released at the source of the earthquake.

14. Magnitude From Amplitude

15. Abbreviated Modified ________ Intensity Scale
Witness observations I
Felt by very few people; barely noticeable II
Felt by a few people, especially on upper floors.
III
Noticeable indoors, especially on upper floors, but may not be recognized as an earthquake. Hanging objects swing. IV
Felt by many indoors, by few outdoors. May give the impression of a heavy truck passing by. V
Felt by almost everyone, some people awakened. Small objects move. Trees and poles may shake. VI
Felt by everyone. Difficult to stand. Some heavy items of furniture move, plaster falls. Slight damage to chimneys possible.
VII
Slight to moderate damage in well-built, ordinary structures. Considerable damage to poorly built structures. Some walls may fall.
VIII
Little damage in specially built structures. Considerable damage to ordinary buildings, severe damage to poorly built structures. Some walls collapse. IX
Considerable damage to specially built structures, buildings shifted off foundations. Noticeable cracks in ground. Wholesale destruction. Landslides. X
Most masonry and frame structures and their foundations destroyed. Ground badly cracked. Landslides. Wholesale destruction. XI
Total damage. Few, if any, structures standing. Bridges destroyed. Wide cracks in ground. Waves seen on ground.
XII
Total damage. Waves seen on ground. Objects thrown up into air.

16. Did You Feel It?

17. Earthquake Hazards ________________ Ground shaking _______________
Ground Rupture

18.
Shaking

19. _________________ Niigata Earthquake, Japan, 1964:
Niigata Earthquake, Japan, 1964:
Tilting of apartment buildings

20. Asian Earthquake and Tsunami of 2004 What Happened and Why?
Magnitude 9 earthquake
Largest earthquake since the 9.2 magnitude Alaskan earthquake (1964)
Energy release equivalent of 23,000 atom bombs such as the one that destroyed Hiroshima
Why did it occur here?

22. Wind-generated Waves vs. Tsunamis

23. Earthquakes and Tsunamis
Landslide, volcano eruptions, asteroid impacts also cause earthquakes
What, besides earthquakes, can cause a tsunami?

24. Tsunami Risk in California
California is at risk of tsunamis that are generated locally and from a distance.
1964: 10 killed and 35 injured when tsunami from the 1964 Alaska earthquake reached Crescent City (Oregon/CA border).
A Cascadia earthquake (an earthquake up in ____________ or ____________ could bring a tsunami to Northern CA in ~ 15 minutes.
Cascadia Earthquake- a quake up in oregon or washington

25. Short-term Prediction
Precursors: May or may not occur
Uplift
Foreshocks
Anomalous animal behavior
Changes in water levels in wells
Release of radon gas
Changes in velocity of P waves

26. Long-Range Forcasting
Based on knowledge of when and where past earthquakes have occurred.
Paleoseismology –
_________________________________________
Seismic gaps-

27. Bay Area EQ Probabilities
Hayward – Rodgers Creek Faults have the highest probabilities
Forecasting (probability) vs. prediction
Source: USGS

28. Paleoseismology - the study of prehistoric earthquakes.

29. M Hayward earthquake
30 fatalities, 5 in San Francisco (12th most lethal US earthquake)
$350,000 (>$5-100M in 2007 dollars) in damage in San Francisco alone
Extensive damage in San Leandro, Hayward, and Fremont (total population less than 2000)
Bay Area population was 260,000 (it is now 27 times larger)
Source: USGS

30. 1868 Hayward
Earthquake
Source: USGS
38°
37.5°
-121°

31. Earthquake of M > 6.8 on the Hayward Fault?
A major earthquake today on the Hayward fault
would impact more than 5 million people and
Cause estimated total economic losses to residential and commercial properties would likely exceed $165 billion.
Other factors, such as fire, damage to infrastructure and related disruption would substantially increase the loss