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Working Group on California Earthquake Probabilities (WGCEP) Development of a

Working Group on California Earthquake Probabilities (WGCEP) Development of a Uniform California Earthquake Rupture Forecast (UCERF). WGCEP Goals:.

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Working Group on California Earthquake Probabilities (WGCEP) Development of a

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  1. Working Group on California Earthquake Probabilities (WGCEP) Development of a Uniform California Earthquake Rupture Forecast (UCERF)

  2. WGCEP Goals: To provide the California Earthquake Authority (CEA) with a statewide, time-dependent ERF that uses “best available science” and is endorsed by the USGS, CGS, and SCEC, and is evaluated by Scientific Review Panel (SRP) and CEPEC & NEPEC Coordinated with the next National Seismic Hazard Mapping Program (NSHMP) time-independent model CEA will use this to set earthquake insurance rates (they want 5-year forecasts, maybe 1-year in future)

  3. UCERF Model Components Fault Model(s) (A) Black Box Deformation Model(s) (B) Black Box (C) Earthquake Rate Model(s) Black Box (D) Earthquake Prob Model(s)

  4. UCERF Model Components Fault Model(s) (A) Black Box Instrumental Qk Catalog Deformation Model(s) Fault Section Database Historical Qk Catalog (B) Black Box (C) Earthquake Rate Model(s) GPS Database Black Box (D) Paleo Sites Database Earthquake Prob Model(s)

  5. Delivery Schedule February 8, 2006 (to CEA) UCERF 1.0 & S. SAF Assessment to CEA Aug 31, 2006 (to CEA) Fault Section Database 2.0 Earthquake Rate Model 2.0 (preliminary for NSHMP) • April 1, 2007 (to NSHMP) • Final, reviewed Earthquake Rate Model • (for use in 2007 NSHMP revision) • September 30, 2007 (to CEA) • UCERF 2.0 (reviewed by SRP and CEPEC) UCERFs ≥3 later

  6. Aug 31 Deliverables: • i. Fault Section Database 2.0: • “… will contain the parameters describing a revised statewide set of fault sections. This statewide set will be sufficient for building Earthquake Rate Model 2.0.” • ii. Earthquake Rate Model 2.0: • “… will be the product delivered to the USGS as USC-SCEC/USGS/CGS input to NSHMP(2007).” • Reality: this will be a preliminary version of what’s ultimately used, as revisions up to the last minute are inevitable (versions 2.X). • NSHMP will have their own public review in October, 2006. • Thus, how polished does the Aug. 31 delivery need to be? • Branch weights will not be included (except maybe preliminary)

  7. Aug 31 Deliverables: • i. Fault Section Database 2.0: • “… will contain the parameters describing a revised statewide set of fault sections. This statewide set will be sufficient for building Earthquake Rate Model 2.0.” • ii. Earthquake Rate Model 2.0: • “… will be the product delivered to the USGS as USC-SCEC/USGS/CGS input to NSHMP(2007).” • Incremental changes to NSHMP (2002) because: • We want to keep track of what changes matter • Don’t promise more than we can deliver • NSHMP consumers don’t want more than this • (more ambitious changes in versions ≥3.0)

  8. Aug 31 Deliverables: • i. Fault Section Database 2.0: • “… will contain the parameters describing a revised statewide set of fault sections. This statewide set will be sufficient for building Earthquake Rate Model 2.0.” • ii. Earthquake Rate Model 2.0: • “… will be the product delivered to the USGS as USC-SCEC/USGS/CGS input to NSHMP(2007).” • Development strategy: • “Focus on what’s important rather than what’s interesting” • Statewide consistency • Simplify wherever possible • Question: • What hazard or loss metric should we use?

  9. Time Span Earthquake- Rupture Forecast List of Adjustable Parameters Intensity- Measure Relationship List of Supported Intensity-Measure Types List of Site-Related Independent Parameters Site Location List of Site- Related Parameters Intensity Measure Type & Level (IMT & IML) Adjustable Parameter Settings Hazard Calculation Prob(IMT≥IML)

  10. UCERF Model Components Fault Model(s) (A) Black Box Deformation Model(s) (B) Black Box (C) Earthquake Rate Model(s) Black Box This is a time- independent ERF (D) Earthquake Prob Model(s)

  11. The ERF Adjustable Parameters are the epistemic uncertainties:

  12. Those in Earthquake Rate Model 2.0 include (so far) :

  13. Easily Added: • Fault Section Database 2.0 Uncertainties for: • slip rate • upper and lower seismogenic depth • aseismicity factors (if available) • average dip for each fault section • Fraction of Mo-Rate on A & B sources into smaller events* • Additional epistemic uncertainty on A- & B-fault mags* • More Work: • Other slip per even assumptions on A-Faults • (other than the characteristic slip; Dsr = Ds): • WG02 Slip (Dsr proportional to vs) • Uniform/Boxcar Slip (Dsr = Dr) • Tapered (Dsr goes down toward ends of rupture) • Others? • Uncertainties in segment mean recurrence intervals • Uncertainties in segment boundaries for A-Faults • Combining some adjacent B-Fault sources These could (should?) be added to Earthquake Rate Model 2.0:

  14. Definitely Not Included in Earthquake Rate Model 2.0: Deformation Models ≥3.0 Fault-to-fault rupture jumps (via generalized inverse or simulations) Relaxation of assumed segmentation while honoring paleoseismic data (which might demand a segmented model) These inherent limits should be kept in mind when deciding how much more work should be put into Earthquake Rate Models 2.x

  15. The outer branches of a logic tree represent an “ERF Epistemic List” (a list of ERFs w/ diff. param. settings & associated weights): How extensively should the logic-tree be sampled? Example with WGCEP-2002 … What will actually be used?

  16. Basic Questions for SRP What more should be accomplished by Aug. 31st? What should be accomplished by April 1 (NSHMP deadline)? What hazard or loss metric should be used? How extensively should the logic-tree be sampled? How shall the branch weights be assigned? How shall the formal review proceed? Fault Section Database 2.0 Fault Models 2.1 & 2.2 Deformation Models 2.x Earthquake Catalog Regional Seismicity Constraints Magnitude-Area Relations Segment Recurrence Data Alt. A-Fault Rupture Models Type-B Fault & C-zone models Recipe for combining everything

  17. Intro to Fault Section Database, Fault Models, and Deformation Models

  18. Hanks & Bakun (2002): M = 3.98 + log(A) if A<537 M = 3.07 + (4/3)log(A) if A>537 Ellsworth A: M = 4.1 + log(A) Ellsworth B: M = 4.2 + log(A) Somerville (2006): M = 3.98 + log(A)

  19. If S segments, then R=S(S+1)/2 different ruptures involving contiguous segments. • We want the long-term rate (fr) of each rth rupture. • We know for each segment: Slip Rate (vs); Mean Recur Int (Ts=1/s) • Constraints are: • Equation Set (1) • Equation Set (2) • Equation Set (3) • Positivity • where Dsr is the average slip in the rth rupture on the sth segment, and Gsr is a matrix indicating whether the rth rupture involves the sth segment (1 if so, 0 if not). Type-A Fault Rupture Models Under-determined (infinite number of solutions)

  20. WGCEP-2002 Solution Requires moment balancing Implicitly assumes Drs is proportional to vs If end segment can’t go alone, then neither can its neighbor.

  21. Assume characteristic slip (like WGCEP-1995): Dsr= Ds= vs/s= vsTs Current WGCEP Solution With compiled Ts (spreadsheet), and vs from the chosen deformation model, solve for the following (by hand): Minimum Rate Solution - That which minimizes the total rate of ruptures (and therefore maximizes event magnitudes), consistent w/ obs. Maximum Rate Solution - That which maximizes the total rate of ruptures (and therefore minimizes event magnitudes), consistent w/ obs. Geological Insight Solution - That which makes all fr as close as possible to a complete set of defined by geologists, consistent w/ obs. • Equal Rate Solution - That which makes all fr as equal as possible (These don’t span solution space, but should span hazard/loss space?)

  22. Current WGCEP Solution Further details: Aseismic Slip Factor applied as reduction of area or slip rate. Each rupture given a Gaussian magnitude PDF w/ default sigma = 0.12 and truncation at +/- 2 sigma.

  23. Current WGCEP Solution Hanks & Bakun (2002): M = 3.98 + log(A) if A<537 M = 3.07 + (4/3)log(A) if A>537 Ellsworth A: M = 4.1 + log(A) Ellsworth B: M = 4.2 + log(A) Somerville (2006): M = 3.98 + log(A)

  24. What needs further consideration (?): Current WGCEP Solution Dependence of tabulated mean recurrence intervals (Ts) on deformation model (vs). Some rupture models are not exactly rate balanced. Influence of mean recurrence interval uncertainties. How well & consistently are these uncertainties defined? Alternatives to the characteristic slip assumption (currently trying to implement a generalized inversion solution using NNLS of Lawson and Hanson (1974)).

  25. Current WGCEP Solution We also have an Un-Segmented option for Type-A faults (same as for Type-B faults).

  26. One for each fault section in the database that is not part of a Type-A fault (although Concord-Green Valley & Greenville are sections combined Type-B Fault Rupture Models • Set the following • 1) Deformation Model • 2) Aseismicity Factor Reduced Area? • Mag-Area Relationship (to get mean and upper mag for char and GR dists) • 4) % Char vs GR • 5) Mag Sigma (for char dist) • 6) Truncation Level (for char dist) • 7) B-Faults b-value (for GR dist) GR lower mag = 6.5. If GR upper mag < 6.5 , all moment-rate goes in the Char dist. NSHMP-2002 used a truncation level of 1.25 sigma (rather than the 2 sigma of WGCEP-2002), but also added an additional +/- 0.2 epistemic uncertainty to both the Char and Upper-GR Mags (not yet done here).

  27. NSHMP-2002 B-Fault exceptions (special cases with “fixed” values): Type-B Fault Rupture Models Owl Lake ( M 6.5, rate 0.002/yr), Owens Valley fault (M7.6, rate 0.00025) The magnitude was fixed at the magnitude of the 1882? (1872) earthquake. Honey Lake fault (M 6.9, rate 0.00067) recurrence rate of about 1500 years based on paleoseismic study by Wills and Borchardt (1991) Eureka Peak ( M 6.4, rate 0.0002) The 5,000 yr recurrence is similar to the other Mojave faults Burnt Mountain (M6.5, rate 0.0002) The 5,000 yr recurrence is the same as other Mojave faults Cucamonga (M6.9, 0.00154) Maximum magnitude and recurrence of about 650 years based on 2 m average recurrence. Sierra Madre-San Fernando (M6.7, 0.001) Magnitude based on San Fernando earthquake, recurrence of 1 ka based on USGS (1996). Palos Verdes (M7.2, 0.00154) Recurrence based on McNeilan et al. (1996) of 650 years. Blackwater (M 6.9, 0.0002) Based on paleoseismic studies by Hecker et al., 1993; Rubin and Sieh, 1993; and Herzberg and Rockwell, 1993. Calico-Hidalgo (M7.2, 0.0002) Based on paleoseismic studies by Hecker et al., 1993; Rubin and Sieh, 1993; and Herzberg and Rockwell, 1993. Gravel Hills-Harper Lake (M7.0, 0.0002) Based on paleoseismic studies by Hecker et al., 1993; Rubin and Sieh, 1993; and Herzberg and Rockwell, 1993. Helendale-S. Lockhart (M7.2, 0.0002) Based on paleoseismic studies by Hecker et al., 1993; Rubin and Sieh, 1993; and Herzberg and Rockwell, 1993. Lenwood-Lockhart-Old Woman Springs (M7.5, 0.0002) Based on paleoseismic studies by Hecker et al., 1993; Rubin and Sieh, 1993; and Herzberg and Rockwell, 1993. Pisgah-Bullion Mountain Mesquite Lake (M7.2, 0.0002) Based on paleoseismic studies by Hecker et al., 1993; Rubin and Sieh, 1993; and Herzberg and Rockwell, 1993. Landers (M7.3, 0.0002) Based on paleoseismic studies by Hecker et al., 1993; Rubin and Sieh, 1993; and Herzberg and Rockwell, 1993. Magnitude based on 1992 Landers qk South Emerson-Copper Mountain (M 6.9, 0.0002) Based on paleoseismic studies by Hecker et al., 1993; Rubin and Sieh, 1993; and Herzberg and Rockwell, 1993. Johnson Valley (M 6.7, 0.0002) Based on paleoseismic studies by Hecker et al., 1993; Rubin and Sieh, 1993; and Herzberg and Rockwell, 1993. Maacama (M 7.5 ) Floated a M 7.5 earthquake because the discontinuous strands of the fault were not thought to be capable of rupturing in a larger event.

  28. For events in areas where deformation is occurring over a wide area on poorly known or unknown faults, modeled as strike slip events oriented along the structural trend (fixed strike); GR between mag 6.5 and 7.3 (except foothills gets mag 6-7); moment rate as: *L*h*slipRate. Type-C Zone Rupture Models 4 New zones:

  29. Background Seismicity • In computing total regional seismicity parameters, Karen recommends several revisions to the NSHMP-2002 method, including: • making corrections for magnitude error and rounding before calculating a values • using only modern instrumental data to calculate b value • leaving aftershocks in the catalog when calculating parameters for the entire study region • using an inverse power law rather than a Gaussian smoothing kernel when calculating spatially variable seismicity rates Results: 14% lower total rate of M≥5 events b-value of 1.0 rather than 0.8 a different spatial distribution or seismicity

  30. Background Seismicity • In computing total regional seismicity parameters, Karen recommends several revisions to the NSHMP-2002 method, including: • making corrections for magnitude error and rounding before calculating a values • using only modern instrumental data to calculate b value • leaving aftershocks in the catalog when calculating parameters for the entire study region • using an inverse power law rather than a Gaussian smoothing kernel when calculating spatially variable seismicity rates Results: 14% lower total rate of M≥5 events b-value of 1.0 rather than 0.8 a different spatial distribution or seismicity Her best estimate of the total rate of M≥5 events is 10+/-1.2 per including aftershocks , and 5.4+/- 0.85 otherwise (and assuming the definition of aftershocks applied by the NSHMP-2002). However, for our definition of “California” (RELM-test region) mult these by 0.75 to get: Rate of M≥5 = 7.5 +/- 0.9 including aftershocks Rate of M≥5 = 4.0 +/- 0.6 excluding aftershocks

  31. Background Seismicity • Background seismicity is computed as the total target rate minus the rates implied by the Type-A, Type–B, and C-zone sources. The adjustable parameters (epistemic uncertainties) are: • Total Rate of M≥5 events (default=7.5 including aftershocks; 4.0 excluding) • Regional b-value (default=1.0) • Maximum Magnitude of Background (default=7 as in NSHMP) • The magnitude frequency distribution for all background seismicity combined is computed as follows: • 1) Create a target cumulative Gutenberg-Richter distribution between magnitude 5.0 and the maximum magnitude of the background seismicity (truncated on the incremental distribution) with the specified b-value and total rate of M≥5 events. • 2) From this target distribution subtract the cumulative magnitude frequency distribution of all the Type-A, Type-B, and C-zone sources. • 3) Set any negative rates in the resultant magnitude-frequency distribution to zero. • What remains is then applied as background seismicity using the relative spatial distribution given in Appendix G (and taking care to lower the relative rates accordingly over the A-Fault, B-fault, and C-zone sources). • Total regional moment rate of model varies with the assumed max-mag of background.

  32. Results Magnitude frequency distributions (MFDs) obtained from Earthquake Rate Model 2.0 with default parameters (listed in Table 1 and shown in Figure 3). The bold black line is the total model MFD, blue is for all Type A sources, green is for the Gutenberg-Richter part of all Type B sources, charcoal is for the characteristic part of all Type B sources, and hot pink is for the background sources. Red is simply a target MFD that should be ignored at high magnitudes.

  33. Results Changing: Mag-Area Relationship = Ellsworth-B Regional b-value = 0.9.

  34. Those in Earthquake Rate Model 2.0 include (so far) :

  35. Easily Added: • Fault Section Database 2.0 Uncertainties for: • slip rate • upper and lower seismogenic depth • aseismicity factors (if available) • average dip for each fault section • Fraction of Mo-Rate on A & B sources into smaller events* • Additional epistemic uncertainty on A- & B-fault mags* • More Work: • Other slip per even assumptions on A-Faults • (other than the characteristic slip; Dsr = Ds): • WG02 Slip (Dsr proportional to vs) • Uniform/Boxcar Slip (Dsr = Dr) • Tapered (Dsr goes down toward ends of rupture) • Others? • Uncertainties in segment mean recurrence intervals • Uncertainties in segment boundaries for A-Faults • Combining some adjacent B-Fault sources These could (should?) be added to Earthquake Rate Model 2.0:

  36. Definitely Not Included in Earthquake Rate Model 2.0: Deformation Models ≥3.0 Fault-to-fault rupture jumps (via generalized inverse or simulations) Relaxation of assumed segmentation while honoring paleoseismic data (which might demand a segmented model) These inherent limits should be kept in mind when deciding how much more work should be put into Earthquake Rate Models 2.x

  37. The outer branches of a logic tree represent an “ERF Epistemic List” (a list of ERFs w/ diff. param. settings & associated weights): How extensively should the logic-tree be sampled? Example with WGCEP-2002 … What will actually be used?

  38. Basic Questions for SRP What more should be accomplished by Aug. 31st? What should be accomplished by April 1 (NSHMP deadline)? What hazard or loss metric should be used? How extensively should the logic-tree be sampled? How shall the branch weights be assigned? How shall the formal review proceed? Fault Section Database 2.0 Fault Models 2.1 & 2.2 Deformation Models 2.x Earthquake Catalog Regional Seismicity Constraints Magnitude-Area Relations Segment Recurrence Data Alt. A-Fault Rupture Models Type-B Fault & C-zone models Recipe for combining everything

  39. SCEC will provide CEA with a single-point interface to the project. WGCEP Organization & Funding Sources CEA Geoscience organizations SCEC NSF Management oversight committee Scientific review panel USGS Menlo Park USGS MOC SRP Sources of WGCEP funding USGS Golden CGS State of CA Working Group on California Earthquake Probabilities WGCEP ExCom Working group leadership … Subcom. A Subcom. B Subcom. C … Task-oriented subcommittees

  40. WGCEP Management: • WGCEP Management Oversight Committee (MOC): • SCEC Thomas H. Jordan (CEA contact)  USGS, Menlo ParkRufus Catchings • USGS, Golden Jill McCarthy • CGS Michael Reichle In charge of resource allocation and approving all project plans, budgets, and schedules Their signoff will constitute the SCEC/USGS/CGS endorsement

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