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The Idea of Earthquake Prediction

The Idea of Earthquake Prediction. Time-independent hazard- random process in time: used for building design, planning, insurance, probability

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The Idea of Earthquake Prediction

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  1. The Idea of Earthquake Prediction • Time-independent hazard-random process in time: used for building design, planning, insurance, probability • Time-dependent hazard-a degree of predictability, enable authorities to prepare for an event-false alarms- loss of public confidence, China- shut down of public services during false alarms

  2. Earthquake Predictions • The 1960’s- descriptions of physical changes • 1970’s- 1975, successful prediction; 1976, 250,000- people died in Tangshen, China • 1980s- Jim Berkland, fluctuations of missing dogs in local newspapers, increase number of calls to satellite TV companies • Greek scientists, electrical signals

  3. Haichen, China, 1975 • An evacuation warning was issued the day before • The local rural population was educated and aided in the monitoring • changes in land elevation and ground water • reports of peculiar animal behavior- snakes coming out of the ground in January, livestock not going into their barns • an increase in small earthquakes

  4. The Idea of Earthquake Prediction or Forecasting • 1977- National Earthquake Hazards Reduction Program (NEHRP) • 1. Precursor detection instruments at the site • 2. Detect and recognize precursors • 3. Get colleagues to agree, accept and put out a warning

  5. Earthquake Forecasts • Earthquake forecasting- some connection between the level of chance between observation and event; probabilities and errors involved • Scientists cannot predict earthquakes • Evacuation before an event since 1975 has not occurred

  6. Long-term Forecasts • Retrofitting • Building codes • Legislation • Insurance • Emergency plans • Education to the public • Preparedness

  7. Long-term Forecasting Methods

  8. Paleoseismicity • Identify fault trace • Trench • Analyze sedimentary layers and offsets • Date organic material

  9. Historical Seismicity Patterns • Large Bay Area earthquakes are more frequent at some times more than others • 1836-1911; 1911-1979 (68 years of no events)

  10. Parkfield Seismic Area 1988-90% probability for a M6 earthquake 1901 1922: 21 years 1934: 12 years 1966: 32 years 2004: 38 years Statistical Method of historic earthquakes Shortest interval: Longest interval: Average: 25.5 years Problems with this method? Recurrence Interval

  11. Pallet Creek offset 1857 1745: 112 years 1470: 275 years 1245: 225 years 1190: 55 years 965: 225 years 865: 100 years 545: 320 years Shortest interval? Longest interval? Average? 187 years Strengths of this method: Shortcomings? Paleoseismology and recurrence interval

  12. Seismic Gaps -areas on a larger fault system that lack seismicity

  13. Variation of average movement on known faults • Bay Area faults belong to the San Andreas fault system • Movement varies • Right-lateral strike-slip faults • 1868- Hayward fault • 1906-San Andreas fault • 1989-San Andreas fault

  14. Variation of average movement on known faults • Bay Area faults move at different rates to accommodate the total amount of slip of the San Andreas fault system • Total+ 34 mm/year • SAF 19 mm/yr • Hayward fault 9 mm/yr

  15. Variation of average movement on known faults Earthquake Prediction and Probability • Each vector represents the amount of movement on each fault • Variations may indicate an imminent earthquake

  16. Pattern of Seismicity

  17. Earthquake Forecasting and Probability • Working Group on California Earthquake Probabilities • Group of 100 geologists, engineers, government officials evaluated all information • Came up with a probability of a magnitude 7 or greater in the next 30 years • 1988. 1999, 2003, 2008

  18. Assumes a random distribution of earthquakes In the Bay Area, 5 earthquakes greater or equal to M 6.75 occur approximately every 30 years 50% probability-just as likely to happen as not to happen Earthquake Forecasting and Probability

  19. The Idea of Earthquake Forecasting • Loma Prieta- 30% probability in 1988- eq, 1989 • Parkfield -90% probability in 1988-eq, 2004 • Landers, Northridge, Kobe- earthquake on a little known fault

  20. Short-term Prediction based on precursors

  21. All the described precursors sometimes occur but as of yet do not occur in a manner that successfully predict earthquakes

  22. What should be expected? • A reasonable time period • The location- fault or fault segment • Magnitude or amount of energy released

  23. Ground Deformations • Ground deformation • Preceding the 1906 earthquake in Marin County-elastic rebound theory • The Palmdale bulge- monitoring began in the 1960’s , associated with the SAF

  24. Radon Gas Emissions • Radon emission- a radioactive gas that sometimes shows an increase preceding an earthquake- • There was a ten-fold increase 30 kilometers away from the epicenter 9 days preceding the earthquake. • Problem with this method?

  25. Parkfield Experiment • Examining precursors or those events that sometimes occur before a main event • Changes in physical properties in close proximity to the fault

  26. Parkfield experiment • Magnitude 6 earthquake occurred on average every 22 years from 1857-2004 • Similar location • Similar seismic wave pattern recorded Hopes of documenting an earthquake before, during, and after the main shock in order to produce a short-term prediction technique.

  27. Precursors expected to observe • Foreshocks • Ground deformation Surface cracks associated with the 2004 earthquake

  28. San Andreas Fault Observatory at Depth: 2004 Examining physical changes to the rocks at depth

  29. Animal Prediction • Unusual animal behavior prior to a disaster • Greece, 373 BC, rats, snakes and weasels deserted days before an earthquake • Advanced vibrations? • Change in electrical charges? • Change in magnetic field? • So far, unable to use unusual animal behavior to predict earthquakes

  30. Chi Chi Earthquke,Taiwan, 1999 • Initial smaller earthquake during the first 4 seconds have higher frequency waves than larger earthquake • The warning could be sent • Seismic waves travel at about 2 miles per second

  31. Detect P-wave arrival Warning system Emergency centers, hospitals, railways Depends on distance to how helpful Japan-March , 2011, M9, Tokyo-stopped trains; cell phone notification; 8-10 minutes tsunami Kobe-fault under city Mexico-11 warnings, M6 or greater Early Warning System

  32. Early Warning System: U.S. • $80 dollars over 5 years • Arrival of P-waves • 3-4 minutes: Cascadia Subduction Zone • 1 minute warning for SAF • 30 seconds: • doctors stop surgery; • Duck and cover • Trains stop

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