tom heaton caltech geophysics and civil engineering
Post on 19-Dec-2015
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Earthquake Alerting … a different kind of prediction
• What if earthquakes were really slow, like the weather?
• We could recognize that an earthquake is beginning and then broadcast information on its development … on the news.
• “an earthquake on the San Andreas started yesterday. Seismologists warn that it may continue to strengthen into a great earthquake and they predict that severe shaking will hit later today.”
If the earthquake is fast, can we be faster?
• Everything must be automated • Data analysis that a seismologist uses must be
automated• Communications must be automated• Actions must be automated• Common sense decision making must be
automated
How would the system work?• Seismographic Network computers provide estimates of the
location, size, and reliability of events using data available at any instant … estimates are updated each second
• Each user is continuously notified of updated information …. User’s computer estimates the distance of the event, and then calculates an arrival time, size, and uncertainty
• An action is taken when the expected benefit of the action exceeds its cost
• In the presence of uncertainty, false alarms must be expected and managed
What we need is a special seismologist
• Someone who has good knowledge of seismology
• Someone who has good judgment• Someone who works very, very fast• Someone who doesn’t sleep• We need a Virtual Seismologist
Virtual Seismologist (VS) method for seismic early warning
• Bayesian approach to seismic early warning designed for regions with distributed seismic hazard/risk
• Modeled on “back of the envelope” methods of human seismologists for examining waveform data• Shape of envelopes, relative frequency content • Robust analysis
• Capacity to assimilate different types of information• Previously observed seismicity• State of health of seismic network• Known fault locations• Gutenberg-Richter recurrence relationship
Full acceleration time history
envelope definition– max.absolute value over 1-second window
Ground motion envelope: our definition
Efficient data transmission3 components each ofAcceleration, Velocity, Displacement, of9 samples per second
P-wave frequency content scales with M (Allen and Kanamori, 2003,
Nakamura, 1988) Find the linear combination of
log(acc) and log(disp) that minimizes the variance within magnitude-based groups while maximizing separation between groups (eigenvalue problem)
Estimating M from Zad
Estimating M from ratios of P-wave motions
SRN
STGLLS
DLA
PLS
MLS
CPP
WLT
Voronoi cells are nearest neighbor regions If the first arrival is at SRN, the event must be within SRN’s Voronoi cell Green circles are seismicity in week prior to mainshock
What about Large Earthquakes with Long Ruptures?
• Large events are infrequent, but they have potentially grave consequences
• Large events potentially provide the largest warnings to heavily shaken regions
• Point source characterizations are adequate for M<7, but long ruptures (e.g., 1906, 1857) require finite fault
Strategy to Handle Long Ruptures
• Determine the rupture dimension by using high-frequencies to recognize which stations are near source
• Determine the approximate slip (and therefore instantaneous magnitude) by using low-frequencies and evolving knowledge of rupture dimension
• We are using Chi-Chi earthquake data to develop and test algorithms
Real-time prediction of ultimate rupture
Bӧse and Heaton, in prep.
slip
Is the rupture on the San Andreas fault?
Distributed and Open Seismic Network
• Just in the gedanken phase• Tens of thousands of inexpensive seismometers running on
client computers.• Sensors in buildings, homes, buisinesses• Data managed by a central site and available to everyone.• It will change the world!
1000 station LA Network (Phase 2)
Number of stations: 1000
Average spacing: 1.5 km
Unaliased frequency: 1 Hz