need for an accurate reno velocity model to understand amplification in the reno basin

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