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Chapter 4: The SFBR Earthquake Source Model: Magnitude and Long-Term Rates

Chapter 4: The SFBR Earthquake Source Model: Magnitude and Long-Term Rates. Ahyi Kim 2/23/07 EQW. SFBR Earthquake Source Model. SFBR earthquake model  Size Locations Magnitude Long-term recurrence rate

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Chapter 4: The SFBR Earthquake Source Model: Magnitude and Long-Term Rates

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  1. Chapter 4: The SFBR Earthquake Source Model: Magnitude and Long-Term Rates Ahyi Kim 2/23/07 EQW

  2. SFBR Earthquake Source Model SFBR earthquake model  Size Locations Magnitude Long-term recurrence rate Earthquake: fixed, floating and back ground Constructed from variety of geologic, geodetic and seismic data

  3. Outline • Compute rate of characterized earthquake, γchar • Long-term occurrence rate and interval • Evaluating the SFBR model

  4. Introduction: Calculating Rupture Source Rates in Complex Model If each segment act as independent rupture source, the rate of earthquake, γwill be Long-term moment release rate of segment Mean moment of earthquakes However, SFBR model allows segments to fail in combination Char: characterized rupture source Fchar: fraction of seismogenic moment rate expended in characterized eq

  5. Steps in the calculation sequence Eq. 4-2a

  6. Estimating the magnitudes and moments of earthquakes Mean characteristic Magnitude: M-logA relations Wells and Coppersmith(1994) Regression of 83 continental eq 4.4 4-5a 4-5b 4-5c WG99 4-5a and 4-5c: 95% bound of 4-5b 4-6a 4-6b Hanks and Bakun(2001) : based on constant stress drop source scaling. For 7<M, L-model scaling of average fault slip U=αL, α=2E-5

  7. Comparison of candidate M-logA relationships

  8. 1906 San Francisco event (1)The 1906 eq is one instance in a global dataset (2)1906 eq is the one of the event which is relevant to SFBR

  9. Weight of M-logA models

  10. Calculating mean moment approximation

  11. Estimating rupture source moment rates

  12. Fault segment moment rate μ=3E11dyne/cm^2 ν： long-term slip rate (Table 3.8)

  13. Regional slip rate constraint Prescott et al. (2001): GPS data between 1992 and 2000 in central California  39.8+-1.2mm/yr Argus and Gordon (2001): GPS and VBLI  39+-2m/yr Long-term estimates DeMets and Dixon (1999) and Prescott et al.(2001):global plate-motion models. 41+-1mm/yr

  14. Defining relative likelihoods of rupture Moment rate for each rupture source: product of available moment rate and the moment-balanced factors, summed across all rupture scenarios

  15. Partitioning moment rate across earthquake types Fchar characteristic earthquake Fchar Fractions of seismogenic moment rate aftershocks Fafter small earthquake Fsmall Fchar + Fafetr + Fsmall = 1

  16. Seismic moment rate in aftershocks Summed moment of aftershock=10% of main shock moment But This is because of some of very large aftershocks If the large aftershocks are removed, 3+-2% Fafter = 0

  17. Seismic moment rate in smaller earthquakes

  18. Magnitude-frequency distributions for faults Pi(M>Mτ) is the probability that the magnitude of rupture i is greater than the threshold value fmi(m) is the magnitude pdf for the ith rupture source

  19. Background earthquakes Based on Gutenberg-Richter distribution For the 1951-1998(M>3) a=3.67(3.6-3.74 at 95% confidence) b=0.89 For the 1836-2001(M>5.5) a=3.94(3.62-4.3 at 95% confidence) b=0.89 Wesson et al.

  20. Results: Long-term earthquake rates in the SFBR

  21. Evaluating the SFBR Model (Regional comparisons) M>6.7 0.031eq/yr b=1.02 M<6.7 b=0.9

  22. Timing of Large EQ on SFBR faults

  23. Evaluating the SFBR Model (Fault-specific comparisons)

  24. Comparison of SFBR model to other models Frequency of events (6.7>M) Andrews and Schwere(2000) 0.0378/yr 1 B=(2/3)b SFBR model 0.031/yr using eq1 in Andrews and Schwere(2000): 0.028/yr Using roll-off model: 0.043/yr

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