Earthquake forecasting Flashcards
What would prediction of an earthquake state?
A specific magnitude, in a stated place at a stated time
What precursory phenomena might prediction be based off?
Animal behaviour
Changes in seismic velocity, groundwater levels or radon emissions
Electromagnetic varations
Foreshcoks
What is the problem with precursory phenomena?
Non statistically valid (most in hindsight)
What is an example of where good eq predictions occurred?
Haicheng 1975 - 7.5
Foreshocks
Good education and public involvement
following year nearby Tangshan killed ~250,000
What problems were associated with L’Aquila 2009?
Poor communication of risk and by Radon lab technician which identified risk led to public distrust exacerbating damages
What is needed to make earthquake prediction valid?
More than a few days in advance to be useful
Must predict the earthquake with an accuracy of a few days
If the prediction is wrong:
Loss of credibility for prediction
Possible lawsuits
What is eq forecasting?
statistical probabiity or eq above a specified magnitude in agiven place for a specific period of time
What is forecasting based on?
Recurrence time estimte
Geodetic monitoring
What can go wrong with using recurrence time with example?
If data is cherry picked like parkfield california and ignores year which doesnt fit pattern it can affect the outcome like when quake from 85-93 didnt occur till 04.
What can be do when we have a long history of eqs in an area?
can estimate avg recurrence but lots of scatter
How is the recurrence time of large eqs estimated when there is only a short history?
Interval between small eqs (can be bias)
How does fault and eqs being fractal allow estimate of recurrence?
Means there is a relationship between number of large and small eqs in a gievn interval
How does statistics used affect the forecasting of recurrence time?
Time indepenent - constant
Time dependent - probability small after last event then grows (probability lower until 2/3 recurrence)
What happens to velocity and strain as you move away fro the fault zone in interseismic?
Both increase
What will strain be like at the fault during the intersesicmic period?
0
What is the best moniroting method for eqs?
Monitoring interseismic strain using geodetics (gps)
WHat are sesimic gaps?
segemnt of active fault that has not experienced a significnt eq in some time
What is the idea behind seismic gaps?
Slip on surrounding faults increase stress onto part of fault segemnt which hasent ruptured increasing risk there over time
What is an example of the seimsic gap theory?
Tohoku eq occured on segemnt with no major eq ruptures but extented beyond the gap
Worrying area is siemic gao near Tokyo
What is mexicos example of a seismic gap?
Guerrero gap
Why is there an empahsis with forecasted shake maps to look at 30 to 50 yr intervals?
Typical lifetime of mortages
What is important for ground motion models?
The assumptions of the model as well as magnitude
What are ground motion models for the new madrid seismic zone derived from?
Known geology, past events (laregley histroical)
What is seismic risk a combinaiton of?
Hazard (probability, shaking intensity) X Consequence
