Time-independent hazard-random process in time: used for building design, planning, insurance,...

• 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

The Idea of Earthquake Prediction

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

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

• 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

The Idea of Earthquake Prediction or Forecasting

• 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

Earthquake Forecasts

Long-term Forecasts

• Retrofitting

• Building codes

• Legislation

• Insurance

• Emergency plans

• Education to the public

• Preparedness

Long-term Forecasting Methods

• Identify fault trace• Trench• Analyze sedimentary

layers and offsets• Date organic material

Paleoseismicity

• Large Bay Area earthquakes are more frequent at some times more than others

• 1836-1911; 1911-1979 (68 years of no events)

Historical Seismicity Patterns

• 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

Paleoseismology and recurrence interval

• 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?

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

• 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

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

Variation of average movement on known faults

• Each vector represents the amount of movement on each fault

• Variations may indicate an imminent earthquake

Earthquake Prediction and Probability

Variation of average movement on known faults

Pattern of Seismicity

• 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

Earthquake Forecasting and Probability

Earthquake Forecasting and Probability

• 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

• Loma Prieta- 30% probability in 1988- eq, 1989

• Parkfield -90% probability in 1988-eq, 2004

• Landers, Northridge, Kobe- earthquake on a little known fault

The Idea of Earthquake Forecasting

Short-term Prediction based on precursors

All the described precursors sometimes occur but as of yet do

not occur in a manner that successfully predict earthquakes

What should be expected?

• A reasonable time period

• The location- fault or fault segment

• Magnitude or amount of energy released

• 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

Ground Deformations

• 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?

Radon Gas Emissions

Parkfield Experiment

• Examining precursors or those events that sometimes occur before a main event

• Changes in physical properties in close proximity to the fault

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.

Precursors expected to observe

• Foreshocks

• Ground deformation

Surface cracks associated with the 2004 earthquake

San Andreas Fault Observatory at Depth: 2004

Examining physical changes to the rocks at depth

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

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

Early Warning System

• 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: 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