Tsunami Hazard Mapping in Crescent City, California

Transcription

Tsunami Hazard Mapping in
Crescent City, California
Nicole Metzger, Michael Baker International
Frank González, U. Washington, Earth and Space Sciences
Darryl Hatheway, AECOM
Randy LeVeque, U. Washington, Applied Mathematics
Loyce Adams, U. Washington, Applied Mathematics
Presented by Steve Eberbach, Michael Baker International
ASFPM CONFERENCE • JUNE 2014
Probabilistic Tsunami Hazard Assessment:
A pilot study in support of the FEMA Risk Map Project
Crescent City Harbor, California
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Model Methods
Map Products
There has been a gradual evolution in tsunami hazards assessment over the last few decades
I.
Worst Considered Case
• A Historic or Paleotsunami event
• Scientifically Defensible
There has been a gradual evolution in tsunami hazards assessment over the last few decades
I.
Worst Considered Case
• A Historic or Paleotsunami event
• Scientifically Defensible
II. Sensitivity Analysis (or Response Study)
• Run a bazillion simulations
• Ignore probability of occurrence
• Keep track of community inundation
III. Probabilistic Tsunami Hazard Analysis (PTHA)
Goal: Find the maximum flood levels that will be exceeded with a given annual probability
100-YEAR TSUNAMI
500-YEAR TSUNAMI
Maximum flooding with 0.01 annual
probability of exceedance
Maximum flooding with 0.002 annual
probability of exceedance
m
m
Basic Methodology: 1. Specify Seismic Sources
1. Specify J = 30 sources of “known” (Poissonian) probability of occurrence pj = 1 ‐ e‐νj ; νj = 1/TMj ; j=1,J
• 15 Far‐field Pacific Rim sources: Deterministic, each with 1 realization and an assigned Recurrence Time, TMj
• 15 realizations of a Near‐field CSZ source: Stochastic, with the realization of each scenario assigned a weight (conditional probability) that yields an overall TM for the CSZ. S. American Source
Basic Methodology: 1. Specify Seismic Sources
1. Specify J = 30 sources of “known” (Poissonian) probability of occurrence pj = 1 ‐ e‐νj ; νj = 1/TMj
• 15 Far‐field Pacific Rim sources: Deterministic, each with 1 realization and an assigned Recurrence Time, TMj
Model 9-13
Mw 8.5-8.8
Model 15
Mw 9.0
Model 1-8
Mw 8.5-8.8
Local Cascadia
Sources (15)
S. American Source
Model 14
Mw 9.2
; j=1,J
• 15 realizations of a Near‐field CSZ source: Stochastic, with each realization of a scenario assigned a conditional probability p = 0.nnn that yields an overall TM for the CSZ.
Basic Methodology: 2. Compute Inundation
1. Specify J seismic sources of “known” (Poissonian) probability of occurrence pj = 1 - e-νj ; νj = 1/TMj
2. Compute the inundation for each source and save the maximum flood depth values, ζ
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; j=1,J
GeoClaw Tsunami Model
Approved by National Tsunami Hazard Mitigation
Program (NTHMP)
Finite Volume
Shock Capture Algorithm
Open Source, with global user community
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Adaptive Mesh Refinement
Fine-grid resolution at source, to capture detail
Coarse grid where no wave exists (including
near the source)
Grid Refinements as needed, to track waves
above specified amplitude
Finest grid at site of interest (Hilo)
; j=1,J
GeoClaw Tsunami Model
Approved by National Tsunami Hazard Mitigation
Program (NTHMP)
Finite Volume
Shock Capture Algorithm
Open Source, with global user community
Adaptive Mesh Refinement
ζ at MLW
5.4 m
ζ at MHW
; j=1,J
5.4 m
• Example is for a 9.1 CSZ scenario
• Uncertainty introduced by the tides is accounted for by improved, newly-developed method for estimating tidal
uncertainty: Adams, et al. (2014) : The Pattern-Method for Incorporating Tidal Uncertainty Into Probabilistic
Tsunami Hazard Assessment (PTHA). Submitted to Natural Hazards (In review).
Basic Methodology: 3. Construct Hazard Curves
1. Specify J seismic sources of “known” (Poissonian) probability of occurrence pj = 1 - e-νj ; νj = 1/TMj ; j=1,J
3. Construct hazard curves P(ζ > ζi | x,y) = annual probability that ζ exceeds (specified) level ζi
Note: If ζ > ζi for the jth source, then pj(ζ > ζi) = 1 - e-νj , and P(ζ > ζi | x,y) = 1 - ∏j (1 - pj) = 1 - ∏j e-νj
103
P(ζx,y)
P(ζx,y)
101
ζ
ζ

104
105
105
104
P(ζx,y)
P( P(
x,y)
ζx,y)
103
 ζ
101
ζ
Basic Methodology: 4. Construct Annual Probability of Exceedance Maps
Basic Methodology
Note: If ζ > ζi for the jth source, then pj(ζ > ζi) = 1 - e-νj , and P(ζ > ζi | x,y) = 1 - ∏j (1 - pj) = 1-∏j e-νj
4. Construct annual probability of exceedance maps for P = 0.01, 0.002, … , etc.
500-year Tsunami
ζ values for P(ζ
•(x,y)
ζ ~3.8 m
Note:
ζ on land = flow depth wrt topography
ζ offshore = wave height wrt MHW
Basic Methodology: 4. Construct annual probability of exceedance maps
Basic Methodology
a. Choose a P value on the Hazard Curve, say P = 0.002, and find corresponding value ζ = 3.8 m
500-year Tsunami
•(x,y)
ζ ~3.8 m
Note:
Basic Methodology: 4. Construct annual probability of exceedance maps
Basic Methodology
a. Choose a P value on the Hazard Curve, say P = 0.002, and find corresponding value ζ = 3.8 m
b. Assign the value ζ = 3.8 m to grid cell (x,y)
c. Repeat for all grid cells (x,y) and contour the ζ values
500-year Tsunami
•(x,y)
ζ ~3.8 m
Note:
Final Products (two complementary maps)
Question: What are the maximum flood levels that will be
exceeded for given annual probabilities ?
Product: Maps of P(ζ ) = 0.01, 0.002, …
100-year Tsunami
P(ζ) = 0.01
500-year Tsunami
P(ζ) = 0.002
Question: What are the maximum flood levels that will
be exceeded for given annual probabilities ?
Question: What are the annual probabilities that
flooding will exceed given levels ?
Product: Maps of ζ(P) = 0, 1, …
100-year Tsunami
P(ζ) = 0.01
500-year Tsunami
P(ζ) = 0.002
ζ(P) = 0
ζ(P) = 1
ζ(P) = 2
ζ(P) = 3
Question: What are the maximum flood levels that will
be exceeded for given annual probabilities ?
Question: What are the annual probabilities that
flooding will exceed given levels ?
Product: Maps of ζ(P) = 0, 1, …
100-year Tsunami
P(ζ) = 0.01
500-year Tsunami
P(ζ) = 0.002
ζ(P) = 0
ζ(P) = 1
ζ(P) = 2
ζ(P) = 3
Summary
 Phase I Completed
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100- and 500-year annual exceedance probability maps for flooding
depth
15 Pacific Rim Far-field Sources; 1 CSZ Stochastic source
 Phase II (near completion)
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Expand suite of CSZ sources. Improve consistency with the 2014
update to US National Seismic Hazard Mapping Program.
Probabilistic maps for
Max wave height, flooding, speed, and momentum flux
 2015
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Use 300+ Cascadia Subduction Zone sources developed by URS that
are optimally consistent with NSHMP guidance
Develop a Source-Reduction Methodology to reduce the number of
sources yet obtain acceptably accurate results.
For More Information
 Final Report
González F.I., R.J. LeVeque R.J., L.M. Adams (2013): Probabilistic
Tsunami Hazard Assessment (PTHA) for Crescent City, CA. Final
Report on Phase I, 1–70,
http://hdl.handle.net/1773/22366
 Contacts
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Frank González: figonzal@u.washington.edu
Randy LeVeque: rjl@uw.edu
Loyce Adams: lma3@uw.edu
Darryl Hatheway: darryl.hatheway@aecom.com
Nicole Metzger: nmetzger@mbakerintl.com

Tsunami Hazard Mapping in Crescent City, California

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