Application of empirical Green’s functions for the construction and validation of the GBCVM

Morgan P. Moschetti and Michael H. RitzwollerCenter for Imaging the Earth’s Interior

Univ. of Colorado, Boulder

Arthur Rodgers and Anders PeterssonLawrence Livermore National Laboratory

GBCVM Workshop, UNRJanuary 14, 2008

Overview

Ambient noise processing for EGFs Dispersion measurements for surface wave

tomography 3-D inversion - shear wave velocity values Comparison of EGFs and synthetics from the

USGS Bay Area 3-D velocity model.

Application to GBCVM (Weaver, 2005)

Ambient Noise Processing for empirical Green’s functions

Ambient Noise Processing for empirical Green’s functions

time (s)0 250100 200

4 – 10 sec

10 – 20 sec

20 – 35 sec

Broadband

time (s)

16 Month Stack

Station Y12C

Station 109C

No

rmal

ized

vel

oci

ty

Distance: 258 km

period (s)

U (

km

/s)

Rayleigh group velocitiesRayleigh group velocities

Rayleigh Wave Group Velocity, 8-sec

Rayleigh Wave Phase Velocity Maps

• 477 stations (USArray TA and regional networks) – 0.5 degree grid

• > 100,000 inter-station paths• Ability to improve local resolution with

higher density arrays• http://ciei.colorado.edu/~morganm

Local Dispersion curves for inversion

Period (s)

Rayleigh wave phase velocity maps

Love wave phase velocity maps

Period (s)

c (k

m/s

), L

ove

c (k

m/s

), R

ayle

igh

Neighbourhood Algorithm to define an ensemble of acceptable models

Period (s)

c (k

m/s

), L

ove

c (k

m/s

), R

ayle

igh

Crustal thickness estimates

Crustal thickness (km)

Upper and middle crust slices

Lower crust and upper mantle slices

Rayleigh waveform comparisons – validation of the USGS Bay Area 3-D Velocity Model

(from collaboration with Rodgers and Petersson, LLNL.)

BKS-MNRC BKS-BNLO

red: EGFgreen: synthetic

Inter-station paths with good measurements

• USGS Bay Area 3-D model – two domains

• 130 common paths (EGF/synthetics)• EGFs limited by stations, synthetics

limited by model.

Rayleigh wave dispersion measurements

period (s)V

elo

city

(km

/s)

period (s)

Group velocities Phase velocitiesBKS - MNRC

period (s)

Vel

oci

ty (

km/s

)

period (s)

Group velocities Phase velocitiesBKS - BNLO

Rayleigh wave 10-sec difference map

Group velocity Phase velocity

Conclusions and Future Work

Empirical Green’s functions within and across Nevada for comparison and inversion.

Shear-wave velocities across Nevada for background values and model/inversion constraint.

Comparison of EGF and synthetic waveforms allows for validation and assimilation of models.

Improved data coverage from higher density arrays.