Long-Period Motions and Fault Slip. Douglas Dreger

Transcription

1 Long-Period Motions and Fault Slip Douglas Dreger

2 Long-Period Motions and Fault Slip It was remarked that long-period motions at sites close to the fault are most sensitive to nearby slip on the fault when we define everything in terms of magnitude this may oversimplify the problem. Suggestions: Check long-period motions (PSd) against fault slip. Check static displacement against fault slip. Compare simulated and GMPE PSd

3 Landers Simulation Fault and Stations LCN JOS Examined the 50 realization of the BBP Landers simulations at the two closest stations, LCN and JOS.

4 Slip Model from One GP/SDSU Simulation JOS LCN

5 Fault Slip Measures Considered Nearest surface slip Maximum radiation weighted FP slip Maximum radiation weighted FN slip Geometric mean of maximum weighted FP & FN slip Geometric mean of FP & FN radiation weighted average slip

6 Compute the Fsh and Fsv, and then project to Fp and Fn radiation pattern from all points on the fault for a given station. Compute the inverse distance scaling (geometric spreading) for all points on the fault for a given station. The product of the radiation pattern term and the spreading defines the fault slip sensitivity and can be used as weights in a weighted average of fault slip.

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8 Compute the Distribution of Fault Slip for 13 stations and 50 simulations to assess whether a single location captures slip variability

9 Nearest Surface Fault Slip Number (13 stations by 50 simulations Slip (cm)

10 Nearest Surface Fault Slip Number Slip (cm)

11 Simulated Ground Displacement at LCN from 50 Source Realizations Both static displacement, and peak displacement are measured from the simulated time histories to compare to nearby fault slip.

12 Static Ground Displacement Compared to Surface Slip and Radiation-Spreading Averaged Slip for LCN Fault Parallel Static Ground Motion (cm) ½ Nearest Surface Fault Slip (cm)

13 Radiation Pattern and Geometrical Spreading Weighted Average of Fault Slip Number (13 stations by 50 simulations) Slip (cm)

14 Radiation Pattern and Geometrical Spreading Weighted Average of Fault Slip Number Slip (cm)

15 Comparison of Static Ground Displacement vs. Rad-Geo Weighted Average Fault Slip Fault Parallel Static Ground Motion (cm) ½ Rad-Geo Weighted Average Fault Slip (cm)

16 Peak FN Ground Displacement Compared to Radiation- Spreading Averaged Fault Slip for LCN

17 Peak FP Ground Displacement Compared to Radiation- Spreading Averaged Fault Slip for LCN

18 Vector Maximum Peak Ground Displacement Compared to Radiation-Spreading Averaged Fault Slip for LCN

19 Geometric Mean PSd: Landers: 50 Simulations: Station LCN 1-3 sec 3-7 sec > 13 sec Psd (centimeters) Period (seconds)

20 Fault Slip vs. Psd Psd (1 to 3 seconds) Radiation and geometric spreading weighted average fault slip (cm)

21 Fault Slip vs. Psd Psd (3-7 seconds) Radiation and geometric spreading weighted average fault slip (cm)

22 Fault Slip vs. Psd Psd (>13 seconds) Radiation and geometric spreading weighted average fault slip (cm)

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24 Comparison of Static Ground Displacement vs. Rad-Geo Weighted Average Fault Slip Station JOS Fault Parallel Static Ground Motion (cm) ½ Nearest Surface Fault Slip (cm)

25 Comparison of Static Ground Displacement vs. Rad-Geo Weighted Average Fault Slip Station JOS Fault Parallel Static Ground Motion (cm) ½ Rad-Geo Weighted Average Fault Slip (cm)

26 Peak FN Ground Displacement Compared to Radiation- Spreading Averaged Fault Slip for JOS

27 Peak FP Ground Displacement Compared to Radiation- Spreading Averaged Fault Slip for JOS

28 Comparison of Simulated, Observed, and GMPE PSd Station LCN ASK2014 BSSA2014 CB2014 CY2014 IM2014 The thick red line is the geometric mean of observed PSd. Plusses show the geometric mean of the two horizontal components from 50 simulations.

29 Comparison of Simulated, Observed, and GMPE PSd Station JOS ASK2014 BSSA2014 CB2014 CY2014 IM2014 The thick red line is the geometric mean of observed PSd. Plusses show the geometric mean of the two horizontal components from 50 simulations.

30 Summary Static displacement, peak displacement, and long-period Psd all correlate with spatially averaged fault slip. The weighted average of fault slip was computed using weights based on the FP and FN radiation patterns with geometrical spreading. PSd from GMPEs are consistent with simulations at long-period.