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11/02/2007 PEER-SCEC Simulation Workshop 1
NUMERICAL GROUND MOTION SIMULATIONS:
ASSUMPTIONS, VERIFICATION AND VALIDATION
• Earthquake Source
• Velocity Structure
• Wave Propagation
11/02/2007 PEER-SCEC Simulation Workshop 2
11/02/2007 PEER-SCEC Simulation Workshop 3
Ti = R / Vr - t (slip)
Vr = Vs
Rupture time derived from simple scaling formula
Coarse slip distribution and hypocenter after Hartzell et al. (1996)
Extend to fine-scale sampling using K-2 filter (e.g. Somerville et al., 1999)
Creating a Rupture Model: Northridge Earthquake
11/02/2007 PEER-SCEC Simulation Workshop 4
TpTr
A
h
Slip Velocity Function
Tr = 2 x 10-9 Mo1/3
Tp = 0.2 Tr
h = 0.2 A
11/02/2007 PEER-SCEC Simulation Workshop 5
11/02/2007 PEER-SCEC Simulation Workshop 6
Rupture Description Issues
• Currently kinematic with dynamic guidance/constraints
• Fully dynamic descriptions are expensive and underlying physics is not completely understood
11/02/2007 PEER-SCEC Simulation Workshop 7
Complex 3D Basin Geology
SCEC CVM
11/02/2007 PEER-SCEC Simulation Workshop 8
1
),,(
1
Ve dV
zyxV
dVzyxV V
e ),,(1
Solution (approximate):
Average media parameters over grid cell volume (effective media parameters)
• Harmonic averaging of Lame parameters (λ and µ)
• Arithmetic averaging of density (ρ)
Spatial Aliasing for Grid Based Models
1
),,(
1
Ve dV
zyxV
11/02/2007 PEER-SCEC Simulation Workshop 9
Velocity Structure Issues
• Different grid-based methods (FEM, SEM, FDM) will “see” slightly different velocity structures.
• Our knowledge of the true velocity structure is not complete: the models will evolve.
11/02/2007 PEER-SCEC Simulation Workshop 10
Verification / Validation of Simulation Methodologies
Verification = Do the codes / methods perform as expected? (theoretical models)
Validation = How well does the method / model predict natural phenomena? (reproduce past observations)
11/02/2007 PEER-SCEC Simulation Workshop 11
Verification Example
11/02/2007 PEER-SCEC Simulation Workshop 12
11/02/2007 PEER-SCEC Simulation Workshop 13
Validation Example: 1994 Northridge EQ
• buried thrust, strong up-dip directivity
• near-fault strong motion recordings at 69 sites
• deep sediment-filled basins
11/02/2007 PEER-SCEC Simulation Workshop 14
Recorded / Simulated Ground Velocity
• pulse-like near fault motions
• extended duration basin motions
General waveform character is matched well-
11/02/2007 PEER-SCEC Simulation Workshop 15
Recorded / Simulated PGA and PGV at 69 Sites
11/02/2007 PEER-SCEC Simulation Workshop 16
11/02/2007 PEER-SCEC Simulation Workshop 17
11/02/2007 PEER-SCEC Simulation Workshop 18
11/02/2007 PEER-SCEC Simulation Workshop 19