Need for an accurate Reno velocity model to understand

amplification in the Reno Basin

Aasha Pancha

Reno Area BasinANSS stations: installed1989 - 2003

Reno Area BasinAbbott and Louie (2000)

1. M=4.4 12/02/2000

2. M=4.49 06/03/2004

1. M=4.4 12/02/2000

Reno Area BasinAbbott and Louie (2000)

• 1D synthetic Green's functions, computed in a layered elastic solid using the generalized reflection and transmission coefficients (Luco and Apsel, 1983; Zeng & Anderson, 1995).

• E3D – fourth order, 3D staggered grid elastic finite difference code (Larsen & Schultz [5]; Larsen & Grieger [6]).

• 0.2 to 0.6 Hz frequency band.

• Compare these simulations with the observed data

Velocity Model = MA

0.25 km grid

RFNV

RFMA

SKYF

1. M=4.4 12/02/2000

2. M=4.49 06/03/2004

2. M=4.49 06/03/2004

Earthquake Locations

Spatial Variation

Insignificant correlation with basin depth

Correlation is significant at the 68% confidence level.

Basin Depth vs Travel Time Residuals

Correlation is significant at the 98% confidence level.

Travel time residuals vs Fourier spectral amplification

Correlation is significant at the 90% confidence level.

Correlation with Vs30 and Vs100V

s100

(98

%)

V

s30

(94%

)

Earthquake Locations

Azimuthal dependence

XX X X

X

X

• Blue = soil to rock (SR) horizontal spectral ratios.

• Red = soil to rock (SRv) spectral ratios of the vertical components of motion.

• Black = horizontal to vertical spectral ratios (HVSR) for individual stations.

• The black dashed = ratio the SR and SRv mean response spectra.

RF10/RFNZ

E N Z

SF02

E N Z

RF11/RFMA

E N Z

RF07/SKYF

E N Z

Summary

• Good agreement is observed between the amplitudes of the data, and that of the 3D simulation.

• E3D matches the durations in the data and may anticipate some of the later arrivals. The 1D code does not.

• 3D basin effects are important and a 3D model is required to model ground motion within the Reno area basin.

• Need for refinement on the velocity and basin structural model.

ID Parameters

• Mo = 5.17E+22 dyne-cm

Calculated:

• Area = 0.894 km

• Rise time = 0.69 seconds

• Slip = 6.3 cm

E3D Parameters

• Grid spacing = 0.25 km

• 77 by 99 km down to depth of 40 km

• Rise time 0.7 seconds Gaussian STF

• to = 0.5 seconds

• Depth 11 km

• dt = 0.015, t=4800 72 seconds

1. M=4.4 12/02/2000

0.2 to 0.6 Hz

Reno Area Basin

Abbott and Louie (2000)ANSS stations:1989-2003

Correlation with Vs30 and Vs100V

s100

(98

%)

V

s30

(94%

)

Spectral Amplification

Spectral Amplification

Spectral Amplification

SR

NGA models

Campbell and Bozorognia (thin dashed line);

Choi and Youngs (thin line);

Boore and Atkinson (dashed-dot line)

UULLA