1. Earthquake Predictions & Tectonic Environments
Natural Disasters
Earthquake Predictions & Tectonic Environments

2. Predicting Earthquakes
Forecast
Involve statements of where and how frequent an event is likely to occur and how large it might be
Predictions
Involve statements about specifically when and where and earthquake is expected to occur

3. Forecasts Reasonable Forecasts:
Most earthquakes will be on plate boundaries
By knowing the type boundary, we can sense the type of motion along faults
Convergent  thrust fault
Divergent  normal fault
Transform  strike-slip
Longer faults produce larger earthquakes

4. Earthquake Predictions
Earthquake Precursors
Seismic Gaps
Migrating Earthquakes
Earthquake Regularity
Paleoseismology
Water as a trigger

5. Earthquake Precursors
Foreshock
Change in surface elevations
Change in water table
Change in radioactivity
Peculiar behavior in animals

6. Earthquake Precursors
Tangshan, China
Haicheng, China (1975)
Successful prediction of 7.3M EQ
Evacuated 1 million people; saved >100,000
90% of buildings severely damaged
Tangshan, China (1976)
No precursors; did not predict 7.6M EQ
250,000 died; 500,000 injured

7. Seismic Gaps A fault segment with few or no historic earthquakes
Upper plot (purple) shows a lack of seismic activity (seismic gap) near Loma Prieta; Lower plot shows seismic gap filled in 1989

8. Seismic Gap Some seismic gaps slip continuously
Stress is relieved w/o an earthquake
Hollister fault (purple) continuously creeps

9. Migrating Earthquakes
In Turkey ( ), EQ moved sequentially westward
Each rupture juxtaposed each other
Seismic gaps later filled with lesser EQ

10. Earthquake Regularity
Fault movement regulated by calendar
i.e. Parkfield, CA
M EQ w/ average 22-year interval
Method uncommon and unreliable

11. Paleoseismology
Study former EQ by measuring offset of rock layers below ground
Trenches across active faults determine ancient fault movement
Amount of offset proportional to magnitude

12. Water as a Trigger Addition of fluids increases pore pressure
Decreases friction between sediments  trigger EQ

13. Long-Term Forecasts and Risk Maps
Based on past activity, frequency, and magnitude
Long-term forecasts requires knowledge of past EQ along fault

14. Surviving Earthquakes
The largest EQ do not kill people, poor construction does
Notice beneath stucco walls, house is built by poorly-cemented rocks

15. San Andreas Fault San Andreas Fault Zone is composed of:
San Andreas fault is main strand
Many parallel faults ~50km width
Dominant EQ zone in U.S.
Continental Transform Fault
Pacific Plate moves northwest relative to North American Plate
1,200 km length in California
Just south of Mexico border to Cape Mendocino in northern CA
Moves at a rate of 3.5 cm/year

16. San Andreas Fault San Francisco Bay Area San Francisco (1906) – 7.8M
Shaking seconds; brick buildings collapsed
500 deaths (early estimate); 3,000 deaths (recent estimate)
Fires burned for days; destroyed 28,000 buildings
dynamite used to stop fire

17. San Francisco Bay Area The Next Big One?
Hayward, Rogers Creek, Calaveras faults
Pose serious threat; last major quake in 1868
62% chance of >6.7M; 80% chance M
Problem – lie beneath heavily populated area
Kobe, Japan (1995)  similar Mag. & pop. density  6,000 deaths

18. San Andreas Fault Los Angeles area Northridge, CA (1994) 6.7M
61 deaths
10,000 bldgs closed; 7 freeway collapse; 170 bridges damaged
Many buildings collapsed due to weak 1st floors

19. Los Angeles Area The Next Big One?
Aside from San Andreas fault, there are many potentially dangerous faults closer to L.A. Metro area
Sierra Madre-Cucamonga, Santa Monica Mtns., Palos Verdes faults
Capable of causing M EQ
Probability of ~6.7M has recurrence interval <10 years; 7.5M  300 years

20. Tectonic Environments & Major Earthquakes
Transform Boundary
Convergent Boundary
Divergent Boundary

21. Transform Boundary
Plates slide past one another

22. Transform Boundary Izmit, Turkey (1999) 7.4M
Similar to San Andreas fault
Arabian & African Plates slide northward against Eurasian Plate
Slippage rate cm/year; 900 km length

23. Convergent Boundary Ocean-continent boundary
Oceanic crust is subducted beneath continental crust

24. Ocean-Continent Chile (1960) 9.5M
Subduction zones produce the largest EQ’s
Large foreshock saves 1,000’s of lives; 2,000 died
Tsunami hit Japan 22 hours after  120 deaths
Expect similar results for the next Cascade Range EQ (Pacific NW U.S.)

25. Convergent Boundary Continent-continent boundary
Build up of huge mountain ranges

26. Continent-Continent Bam, Iran (2003)
Arabian Plate collides with Eurasian Plate  Caucasus Mtns.
3.0 cm/year convergence
6.7 M  similar to Northridge
61 deaths (Northridge); 26,000 deaths (Bam)
The increase in deaths due to poor construction

27. Convergent Boundary Ocean-ocean boundary
Older, colder oceanic plate is subducted

28. Ocean-Ocean Kobe, Japan (1995) 7.2M Very shallow EQ
5,000 deaths, 190,000 buildings destroyed

29. Divergent Boundary Spreading Zones
Extensional forces pulls plates apart

30. Basin & Range Basin & Range Basin & Range in Nevada & Utah
Numerous north-trending normal faults
Faults separate dropped valleys (basins) and uplifted mountains (ranges)