WAACY Magnitude PSF Model (Wooddell, Abrahamson, Acevedo-Cabrera, and Youngs) Norm Abrahamson DCPP SSC workshop #3 Mar 25, 2014

Transcription

1 WAACY Magnitude PSF Model (Wooddell, Abrahamson, Acevedo-Cabrera, and Youngs) Norm Abrahamson DCPP SSC workshop #3 Mar 25, 2014

2 UCERF3 Allowing larger magnitudes by linking rupture segments Grand inversion used, but not simple to use in site-specific studies How do we address these larger magnitudes in a simpler way? How do we constrain the high magnitude part of the magnitude pdf? How often do these linked ruptures occur?ucerf3

3 Typical Example: Hayward Fault

4 What data can we use to constrain the high magnitude part of the Mag pdf? Variability of Slip at a Point Hecker et al. (BSSA, 2013) quantified the characteristic earthquake by exploring coefficient of variation (C.V.) values of surface ruptures: 505 slip-at-a-point observations from 171 sites in 20 countries Average number of observations per site is approx. 3 Approx. 65 sites (~40%) considered most reliable. C.V. (subset dependent): ~

5 Constraints on the high magnitude part of the Mag pdf Approach: Evaluate the upper-bound rates of large magnitude rupture without violating Hecker s observations of surface rupture variability Limitation: Constraint depends on the correlation of magnitude and slip. Steeper the Disp(M) slope, the stronger the constraint. If Disp is independent of M, then no constraint from this method.

6 Forward Modeling Results: Hayward Fault CV ~ CV ~ Empirical Dataset: CV = ~

7 Modified Y&C Model

8 Approach to Constrain Mag pdf Select a Disp(M) model Wells &Coppersmith (1994) all fault types Hecker et al (2013) fit to Wesnousky (2008) data Shaw (2013) Assume a mag pdf (tail model) B-tail and offset Compute the distribution of slip at a point Compute the CV of the observed slip at a point Account for same sampling per site and detection thresholds as the data used by Hecker et al (2013) Does this CV fall within the range from Hecker et al (2013)? Tail model is allowed or rejected

9 Disp(M) Models

10 Mag-Disp Models

11 Model Parameter Space: WC94 Disp(M) model Solutions Inconsistent with Empirical Dataset More Like Y&C Model Solutions Consistent with Empirical Dataset More Like Y&C Model

12 Model Parameter Space: WES Disp(M) model Solutions Inconsistent with Empirical Dataset More Like Y&C Model Solutions Consistent with Empirical Dataset More Like Y&C Model

13 Shaw (2013) model Weak scaling of Disp with Mag for M>7.5 Provides little constraint on the mag pdf for large magnitudes All models considered satisfy the CV < 0.55 constraint

14 Example Results: W&C (1994) Disp(M)

15 Example Results: Wesnousky (2008) Data for Disp(M)

16 Summary of constraint on mag pdf Rate of MChar+1 W&C (1994) model Factor of 500 below rate of MChar WES model Factor of below rate of Mchar Shaw (2013) model Factor of 1 below rate of Mchar

17 Example: simple application of WAACY

18 WAACY Model Strengths Provides a method to get at the high magnitude part of the magnitude pdf Limitations Intended only as an upper bound Assumes reduced aleatory variability compared to global models Ave Disp for a given mag (SigmaLog10 = 0.1) Along strike (CV = 0.3) Constraints depend on the correlation between magnitude and disp

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20 Simple Implementation Issue: How to address ruptures that go outside of the study region How to avoid making the region bigger and bigger to capture all of the linked ruptures?

21 Linked Ruptures

22 Simple Implementation Approach: Key assumption: For each rupture, Ave slip on modeled rupture = Ave slip full For moment balance, only add up the fraction of the moment released on the modeled rupture Additional Assumption: Closest distance is captured by the modeled part of the rupture

23 Hazard Implementation for Large Maximum Magnitudes Typical Fault: Adjust Mo(M) for linked ruptures beyond the modeled fault:

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25 References Hecker, S., N. Abrahamson, and K. Wooddell (2013). Variability of Displacement at a Point: Implications for Earthquake Size Distribution and Rupture Hazard on Faults, BSSA, April 2013, v. 103, p Wooddell, K. and N. Abrahamson (2013). Constraints on Magnitude- Frequency Distributions for Evaluating the Hazard of Multi-Segment Ruptures, Abstract, SSA, April 19, 2013