Cascadia Interface Intraslab Crustal seismic sources Earthquake

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Cascadia Interface Intraslab Crustal seismic sources Earthquake Powered By Docstoc
					Probabilistic Ground Motions
for Scoggins Dam, Oregon
Chris Wood
Seismotectonics & Geophysics Group
Technical Service Center

                                     July 2012
Scoggins Dam
• 45 km east of locked
  part of CSZ interface
  (red)
  – M 9.0 megathrust
    earthquakes
• 60 km above slab (blue,
  green)
  – M 7.5 deep earthquakes
       Reclamation Dam Safety
             Guidelines
• Use risk-based approach for decision making
  that evaluates the following risks:
  – annual probability of failure
  – annualized loss of life
• Consider a wide range of loading conditions to
  determine risk

Probabilistic seismic loadings are needed for input
  into engineering analyses of how dams respond
  to seismic loadings
  – Specifically, we need scenario ground motion time
    histories for a wide range of return periods
How probabilistic ground motions were
    developed for Scoggins Dam
• Perform a Probabilistic Seismic Hazard Analysis (PSHA)
  to get hazard curves, uniform hazard spectra (UHS), and
  disaggregation of hazard
• Determine response spectra for scenario earthquakes
  using the Conditional Mean Spectrum (CMS) method
• Select initial time histories that are representative of the
  main contributors to the hazard
   – from historical records (e.g., M 9.0 Tohoku, Japan)
   – from Empirical Green’s Function (EGF) models
• Spectrally match the selected initial time histories to the
  scenario earthquake response spectra
               Seismic sources
               • Subduction
                  zone
                  interface
               • Intra-slab
                  (deep)
                  earthquakes
               • Crustal:
                  mapped
                  faults and
                  shallow
                  background
                  seismicity



Source: USGS
                PSHA

• Probabilistic seismic hazard analyses
  (PSHA) conducted by R. LaForge, Fugro
  Wm. Lettis & Assoc. (FWLA) for
  Reclamation, 2006, 2009, 2011
• Considered commonly recognized
  earthquake sources (CSZ interface,
  intraslab, and crustal)
          Earthquake Sources used for PSHA


                      Puget intraslab

CZS Interface




                           Portland intraslab
Crustal faults




                                        Cascadia (Interface), Intraslab
                                        & Crustal seismic sources
                                                   PHA Hazard
                                   Scoggins Dam PHA Hazard

                   1.E-01                                                      10                                • 10,000-yr PHA =
                                                        Total                                                      1.4 g
                                                        Interface-only
                                                        Intraslab Sources                                        • Mean hazard
                   1.E-02                               Crustal Sources        100                                 contributors (for
                                                                                                                   return periods of




                                                                                          Return Period, years
Annual Frequency




                                                                                                                   interest):
                   1.E-03                                                      1,000                                1) Cascadia SZ
                                                                                                                       Interface
                                                                                                                    2) Portland
                   1.E-04                                                      10,000
                                                                                                                       Intraslab
                                                                                                                    3) Crustal sources
                                                                                                                       (Gales Creek
                                                                                                                       fault)
                   1.E-05                                                       100,000
                         0.00   0.50        1.00         1.50               2.00
                                           PHA, g
Contributions by source – PHA
                                   Scoggins Dam PHA Hazard Contribution by Source
                          1

                                  Interface
                                  Intraslab

                         0.8      Crustal
 Relative Contribution




                         0.6                                                50,000-yr

                                                  5,000-yr
                                                             10,000-yr
                         0.4
                                       1,000-yr



                         0.2




                          0
                           0.00         0.50       1.00            1.50     2.00        2.50
                                                          PHA, g
                        0.75-sec. SA Hazard – All Sources
                                   Scoggins Dam 0.75-Sec SA Hazard

                   1.E-01
                                                             Total
                                                                                  10
                                                                                                                    • 10,000-yr
                                                             Interface-only
                                                             Intraslab Sources
                                                                                                                      SA = 1.7 g
                                                                                                                    • Mean
                   1.E-02                                    Crustal Sources      100




                                                                                             Return Period, years
Annual Frequency




                                                                                                                      hazard
                   1.E-03                                                         1,000
                                                                                                                      contributors
                                                                                                                      (for return
                   1.E-04                                                         10,000
                                                                                                                      periods of
                                                                                                                      interest):
                   1.E-05                                                          100,000
                         0.00   0.50      1.00       1.50        2.00          2.50                                   1) Cascadia
                                           0.75-Sec SA, g
                                                                                                                         SZ
                                                                                                                         Interface
                                                                                                                      2) Crustal
Contributions by source – 0.75-sec. SA
                                      Scoggins Dam 0.75-Sec SA Hazard Contribution by Source
                              1

                                        Interface
                                        Intraslab
                             0.8        Crustal
     Relative Contribution




                                                                                           50,000-yr
                             0.6                                          10,000-yr
                                                               5,000-yr

                                             1,000-yr
                             0.4




                             0.2




                              0
                               0.00        0.50         1.00         1.50         2.00   2.50          3.00
                                                                0.75-sec SA, g
Computed
 hazard
 strongly
 depends
 on
 subjective
 GMPE
 weights
        Ground Motion Prediction
    Equations (GMPEs) and Weighting
•    Cascadia Subduction Zone Interface
      – Atkinson & Boore, 2003 (worldwide): 0.1 (predicts lowest ground motions for R <
        150 km)
      – Atkinson & Macias, 2009: 0.1
      – Youngs et al, 1997: 0.3
      – Zhao et al, 2006: 0.5 (predicts highest ground motions for R < 150 km)
•    Cascadia Subduction Zone Intraslab
      – Atkinson & Boore, 2003 (worldwide): 0.17
      – Youngs et al, 1997: 0.0
      – Zhao et al, 2006: 0.83
•    Shallow Crustal Sources
      –   Abrahamson & Silva, 2008 (NGA): 0.25
      –   Boore & Atkinson, 2008 (NGA): 0.25
      –   Campbell & Bozorgnia, 2008 (NGA): 0.25
      –   Chiou & Youngs, 2008 (NGA): 0.25

Note: Same GMPEs and weights used both for PSHA and for development of
   scenario response spectra
                 Median CSZ interface deterministic spectra
                                     Deterministic spectra, median
                                                                                        • ZEA06 gives
                           1.0
                                                                     AB03 - ε=0           much larger
                                                                     AM09 - ε=0
                           0.8
                                                                     YEA97 - ε=0          estimated
Spectral Acceleration, g




                           0.6
                                                                     ZEA06 - ε=0
                                                                     Mean
                                                                                          accelerations

                           0.4



                           0.2



                           0.0
                              0.01       0.1                    1                  10
                                               Period, sec.
Comparison
 of M 9.0
 Tohoku,
 Japan EQ
 observatio
 ns with
 GMPE
 predictions
        Scenario Response Spectra
               Development
• Scenario spectra were developed using the Conditional
  Mean Spectrum (CMS) method developed by Baker &
  Cornell, 2006
       • Requires specification of one or more critical spectral response periods
       • If the critical periods of a structure are poorly known, may require target
         spectra from numerous trial periods to fully envelope total hazard
         defined by UHS
       • Provides a more realistic response spectrum for a single earthquake
         than the UHS
• For Scoggins, simplified to long- and short-period scenario
  spectra
   – Results in larger ground motions, but fewer time histories to analyze
• Scenario spectra constraints
   – Scenario spectra for a specified return period envelope the UHS
   – No scenario spectrum is allowed to exceed the UHS
Uniform Hazard Spectra (UHS)
                                            Scoggins Dam UHS

                            6.0
                                                                   Total - 50k UHS
                                                                   Total - 10k UHS
                            5.0                                    Total - 5k UHS
                                                                   Total - 1k UHS
                                                                   Total - 500-yr UHS
                            4.0
 Spectral Acceleration, g




                            3.0


                            2.0



                            1.0


                            0.0
                               0.01   0.1                      1                        10
                                                Period, sec.
                                 Development of CMS Spectra
                                          CMS Method - AM09, 10k Scenario, Tc=0.75 sec

                           3.0                                                                        4.0
                                 Rrupt = 47 km                                      10k UHS
                                 M = 9.0, ε = 2.13
Spectral Acceleration, g




                                                                                    SA(ε=2.13)
                                                                                    SA(ρ?ε)
                           2.0                                                                        3.0
                                                                                    ρ(Tc=0.75,T)



                           1.0                                                                        2.0

                                                                    ε = 2.13
                                                     ε = 1.14
                                      ε = 0.76
                           0.0                                                                        1.0




                                                                                                            Correlation
                                                                    0.75-sec.
                                                                    Critical
                           -1.0                                      Period                           0.0
                               0.01               ρ =0.1
                                                      0.54            ρ=1       1                10
                                      ρ = 0.36
                                                                Period, sec.
CMS – CSZ Interface, 10k, Tc=0.75 sec.
                                         CMS Method - 10k Interface scenario - Tc = 0.75 sec.


                                                                                            ZEA06

                             3.0                                                            YEA97
                                                                                            AM09
                                                                                            AB03
                                                                                            Interface CMS
  Spectral Acceleration, g




                                                                                            10k UHS
                             2.0




                             1.0




                             0.0
                                   0.0                 0.1                      1.0                         10.0
                                                                Period, sec.
CMS – Crustal sources, 10k, Tc=0.75 sec.
                                          CMS Method - 10k crustal scenario - Tc=0.75 sec.

                                                                                             AS08
                                                                                             BA08
                              3.0
                                                                                             CB08
                                                                                             CY08
                                                                                             Crustal CMS
   Spectral Acceleration, g




                                                                                             10k UHS
                              2.0




                              1.0




                              0.0
                                    0.0               0.1                      1.0                     10.0
                                                               Period, sec.
   Time History Development
• Obtain initial time histories for scenario
  earthquakes from historical or synthetic records
  with magnitudes, distances and characteristics
  representative of the Cascadia interface,
  crustal, and intraslab sources
• Use a wavelet-based spectral matching method
  to modify the initial time histories so that the
  response spectrum of the final time history
  matches that of the scenario spectrum
• Match spectra for 500, 1,000, 5,000, 10,000,
  and 50,000 year return periods
CSZ interface source characteristics
 (M, RRupt,ε) for PHA, 10k, YEA97
                            • Largest
                              contribution
                              from M 9.0,
                              and RRupt
                              45-50 km
                            • Similar
                              results for
                              other return
                              periods,
                              response
                              spectral
                              periods, and
                              GMPEs
   Cascadia interface initial time
             histories
• Historical records from 3/11/2011 M 9.0
  Tohoku, Japan earthquake
• Synthetic M 8 to 9 Cascadia interface
  earthquake records based on Empirical
  Green’s function (EGF) method.
HKD070
         EGF
               HKD070 EGF
               • R = 104 km
               • M 6.4
                 aftershock of
                 2003 M 8.0
                 Tokachi-oki,
                 Japan
                 earthquake
               • Soil site
• Simulation
  using EGF
  with R = 100
  km
• Rupture length
  is 600 km
• Hypocenter in
  center
• HKD070 (soil)
• Duration ~ 130
  sec
                 Spectrally-matched
                   5k time history for
                   CSZ interface
                   earthquake source
                 • Initial time history: M
                   9.0 EGF simulation
                   using HKD070 EGF
Spectral Match   • Target spectrum: 5k
                   interface, CMS
                 • PHA = 0.56 g
                 • Duration = 180 sec
                 • IA = 30.2 m/s
Comparison of target and matched response
                  spectra
                                • Target and
                                  matched
                                  response
                                  spectra, 5k
                                  CSZ
                                  interface
                                  from M 9.0
                                  EGF
                                  simulation
                                  using
                                  HKD070
                                  EGF
  Non-interface Time Histories
• Initial time histories representing crustal
  earthquake source (Gales Creek)
• Initial time histories representing the
  Portland intraslab
• Spectrally matched to CMS non-interface
  scenario spectra
• Initial time histories selected from
  historical strong-motion records based on
  PSHA disaggregation results
       Initial
                 Spectrally-matched
                   5k time history for
                   crustal earthquake
                   source
                 • Initial time history: M
                   6.5, 1992, Big Bear,
Spectral Match
                   CA, Big Bear Lake,
                   R=9 km
                 • Target spectrum: 5k
                   non-interface, CMS
                 • PHA = 0.96 g
                 • Duration = 10 sec
                 • IA = 11.2 m/s
Scenario Earthquake Time History
           Summary
• Seven sets of 3-component time histories for
  each scenario spectra.
  – Time histories for CSZ interface, CSZ intraslab, and
    crustal fault scenarios
  – Five return periods: 500, 1,000, 5,000, 10,000 and
    50,000 years
  – Baseline-corrected acceleration, velocity and
    displacement
• Free-surface acceleration time histories
• Velocity time histories for use as compliant base
  input to FLAC model

				
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