11/02/2007 PEER-SCEC Simulation Workshop 1

NUMERICAL GROUND MOTION SIMULATIONS:

ASSUMPTIONS, VERIFICATION AND VALIDATION

• Earthquake Source

• Velocity Structure

• Wave Propagation

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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

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TpTr

A

h

Slip Velocity Function

Tr = 2 x 10-9 Mo1/3

Tp = 0.2 Tr

h = 0.2 A

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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

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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)

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Verification Example

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Validation Example: 1994 Northridge EQ

• buried thrust, strong up-dip directivity

• near-fault strong motion recordings at 69 sites

• deep sediment-filled basins

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Recorded / Simulated Ground Velocity

• pulse-like near fault motions

• extended duration basin motions

General waveform character is matched well-

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Recorded / Simulated PGA and PGV at 69 Sites

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