SDSU Module Kim Olsen and Rumi Takedatsu San Diego State University

Transcription

1 SDSU Module Kim Olsen and Rumi Takedatsu San Diego State University SWUS GMC Workshop #2, Oct 22-24, 2013

2 Question: Based on the June SCEC Meeting, is the output of the BBP consistent with the expectations from your method? Is there anything in the simulations that stand out as problematic? No, but let me explain anyway..

3 Localized outliers (usually peaks) from SDSU scattering approach 3

4 Illustration of Scattering Effects 4

5 With and Without Small-scale Scattering 5

6 0.2 s SA for SDSU compared to GMPEs Ztop=3km 6

7 M w 5.5: Is there anything intrinsic to the method that would preclude using it to simulate small magnitudes (M~5.5)? No. We find an acceptable match to GMPEs for M w 5.5. M w 5.5 ss 50 km M w 5.5 ss 20 km

8 M5.5 Dip=10 deg foot wall hanging wall

9 Question: Is there a model resolution limit on the kinematic representations of the subfaults? About 1Hz, above which we don t use the subfault representation directly Given the specifications of the subfault dimension, is there an effective bandwidth that we should be aware of? 0-1Hz for the finite-fault source, which is the bandwidth used for the SDSU method (>1Hz is represented by scattering functions)

10 Single fault SDSU M5.5 Rake 90 o Dip 10 o Ztop 2.5 km realization No No. of subfaults = 3364 Subfault dimensions ~100 m x 100 m Sufficiently small to model Frequencies up to 1Hz

11 Question: Are there constraints on the use of the magnitude-area relationship that you apply for your simulation method? Only constraints that may be associated with the rupture generator.

12 Is there anything intrinsic to the method that would preclude using it to simulate very large magnitudes (M~8.0)? No 0.5 s 0.2 s 0.1 s 12

13 Question: Are there implications that arise from specifications of a minimum rupture width for large magnitudes? No, other than ground motions may be unrealistically large, if the width is unrealistically small

14 Question: Can the model be applied to both surface and buried ruptures? Yes

15 No Bias From Depth to Top of Fault Event Depth GOF Landers (ss) Tottori (ss) Niigata (rev) LOMAP (robl) N P Springs (robl) Northridge (rev) Whittier (rev) Whittier Whittier Northridge Landers M6.6ss 0.00 best GMPE M6.6rv 3.00 good M6.2ss 4.00 as good M6.6rv M6.6ss

16 Question: Are the Green s functions adequately sampling the shallow depth? Yes

17 Question: How is the source modified in the top few kilometers of the crust (e.g., rise time, rupture velocity, etc )? V r = τ i = 0.56 V s z<5 km 0.8 V s z>8km 2 x k s ½ i z< 5km k x s ½ i z> 8km V r = rupture speed, V s = shear wave speed τ i = rise time for ith subfault, k scaling factor to fault-wide rise time, s i = slip on ith subfault

18 Question: How is the source modified in the top few kilometers of the crust (e.g., rise time, rupture velocity, etc )? τ A = α T M o 1/3 τ A is the average rise time over the entire fault α T = 1 δ > 60 o 0.82 δ < 45 o α T scales the average rise time as a function of fault dip (linear interpolation between 45 o and 60 o ).

19 If the prescribed rupture plane is mostly/fully contained in this shallow region, shallow fault dip cases, does the source modification still apply? I believe so, but there are no observations to constrain. 19

20 Question: Are there any limits in how close to the fault the ground motion simulations may be used? Theoretically, no.

21 Check on near-fault stations: 1-3 km Landers Tottori 21

22 Question: How is kappa incorporated into the simulations? kappa is incorporated into BBtoolbox in the frequency domain for the HF acceleration spectrum as A(f) = Scatterogram(f) x exp(-π κ f)

23 References Dreger, D., E. Tinti, and A. Cirella (2005). Slip velocity function parameteriation for broadband ground motion simulation, Seismol. Soc. Am 2007 Annual Mtg, Waikoloa, Hawaii, April Graves, R.W., and A. Pitarka (2010). Broadband ground-motion simulation using a hybrid approach, Bull. Seis. Soc. Am. 100, 5A, , doi: / Hole, J.A. (1992). Non-linear high resolution three-dimensional seism travel time tomography, J. Geophys. Res. 97, Joyner, W.B., and D.M. Boore (1986). On simulating large earthquakes by Green s function addition of smaller earthquakes, in Earthquake Source Mechanics, Geophysical Monograph 37, Maurice Ewing Vol. 6, Eds S. Das, J. Boatwright, and C.H. Scholz. Leonard, M. (2010) Earthquake fault scaling: self-consistent relating of rupture length, width, average displacement, and moment release, Bull. Seis. Soc. Am. 100, 5A, Mai, P.M. and G.C Beroza (2003). A hybrid method for calculating near-source, broadband seismograms: Application to strong motion prediction, Phys. Earth Planet. In. 137, no 1-4, Mai, P.M., W. Imperatori and K.B. Olsen (2010). Hybrid broadband ground-motion simulations: combining long-period deterministic synthetics with high-frequency multiple S-to-S backscattering, Bull. Seis. Soc. Am. 100, 5A, , doi: / Mena, B., P.M. Mai, K.B. Olsen, M.D. Purvance, and J.N. Brune (2010). Hybrid broadband ground-motion simulation using scattering Green s functions: application to large-magnitude events, Bull. Seis. Soc. Am. 100, 5A, , doi: / Zeng, Y.H., K. Aki, and T.L. Teng (1993). Mapping of the high-frequency source radiation for the Loma Prieta earthquake, California, J. Geophys. Res 98, no. B7, Zeng, Y.H. F. Su, and K. Aki (1991). Scattering wave energy propagation in a random isotropic scattering medium 1. Theory, J. Geophys. Res. 96, no. B1,

24 Thank you for your attention! 24