Seismic Hazard in the Basin and Range Province

Seismic Hazard in the Basin and Range Province, U. S. A. Aasha Pancha

Seismic Hazard Analysis • Earthquake occurrence rates PLUS • Ground motion prediction

Basin and Range Province Reno

Faults Geodetic strain rates Faults with slip rates greater than 0. 1 mm/yr. nanostrain/yr

Moment Rate Comparison

Rate from historical seismicity Slip predictable Time predictable

Moment Rate Comparison

Models to relate deformation rates to seismic moment rates For a fault with average geological slip rate Anderson (1979) For broad zones of deformation, the slip rate can be replaced by the strain rate.

Anderson (1979) Volumetric strain in multiple directions Savage and Simpson (1997) Working Group CEP (1995) Ward (1994, 1998 a, b)

Basin and Range Comparison

Catalog adequacy parameter I suggest that when Z >1. 5 km 2, the observation period in the seismicity catalog is likely to be long enough to yield a stable estimate of the rate.

Characterization of ground motion amplification and correlation with near-surface geology at strong-motion stations in the vicinity of Reno, Nevada.

Reno Area Basin Abbott and Louie (2000)

1. M=4. 4 12/02/2000 2. M=4. 49 06/03/2004

1. M=4. 4 12/02/2000

1. M=4. 4 12/02/2000 0. 2 to 0. 6 Hz

1. M=4. 4 12/02/2000 2. M=4. 49 06/03/2004

2. M=4. 49 06/03/2004

$Refraction Microtremor Propagation velocity is frequency dependent.$

Refraction Microtremor Propagation velocity is frequency dependent.

Vs versus 1: 250, 000 geology

Vs versus 1: 24, 000 geology

Statistical Analysis of classifications Ftest statistics suggest that separation of the individual velocity measurements into geological classifications significantly reduce the variance of the data. However, insufficient data within each classification mean that velocity ranges and correlation with these classifications are not well determined.

Vs versus soil sediment content

Empirical site response and comparison with measured site conditions at ANSS sites in the Reno area

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.

Vs 100 (98%) Vs 30 (94%) Correlation with Vs 30 and Vs 100

Spectral Amplification

NGA models Campbell and Bozorognia (thin dashed line); Choi and Youngs (thin line); Boore and Atkinson (dashed-dot line)

Azimuthal dependence

Earthquake Locations

X X X X

Conclusions • Geodetic deformation has the same spatial distribution as the seismic moment release and earthquake numbers. • Within uncertainties, the rate of historical earthquakes agrees with the rate predicted from the geodesy, and provides a reasonable estimate of future rates of activity. • On a large scale, input to seismic hazard analysis should be consistent with geodetic deformation rates. • Further investigation of conditions for the similarity of seismicity and geodesy is needed.

Conclusions • Rock sites are variable. • Amplification is dependent on whether station is located within the basin. Within the basin amplification is non-uniform. • Both near surface low velocity sediment, and the basin thickness as a whole, have an influence on ground motion amplification within the basin. • Vs 30 more useful than geology or basin depth. • Lack of resonance peaks at many basin sites is consistent with a lack of strong impedance contrast within basin sediments. • Ground motions are affected by azimuthal dependence of incoming waves highlighting that 3 D basin effects are significant.

Publications • Pancha, A. , J. G. Anderson, J. N. Louie, A. Anooshehpoor, and G. Biasi, (2004) Data and simulation of ground motion for Reno, Nevada: Proceedings of the 13 th World Conf. on Earthquake Engineering, Vancouver, B. C. , Aug. 1 -6, paper no. 3452. • Pancha, A. , J. G. Anderson, and C. Kreemer (2006), Comparison of seismic and geodetic scalar moment rates across the Basin and Range province, Bulletin of the Seismological Society of America, 96, 11 -32, doi: 10. 1785/0120040166. • Pancha, A. , J. G. Anderson, G. Biasi, A. Anooshepor, and J. N. Louie (2007). Empirical site response and comparison with measured site conditions at ANSS sites in the Reno area, submitted to the Bulletin of the Seismological Society of America, (accepted), 97 -6, December 2007. • Pancha, A. , J. G. Anderson, G. Biasi, A. Anooshepor, and J. N. Louie (2007). Empirical site response and comparison with measured site conditions at ANSS sites in the Reno area, submitted to the Bulletin of the Seismological Society of America. • Pancha, A. , J. G. Anderson, J. N. Louie, S. Pullammanappallil (2007). Measurement of shallow shear wave velocities at a rock site using the Re. Mi technique, submitted to Soil Dynamics and Earthquake Engineering, in second revision.

Questions

• 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.

Spatial Variation

Re. Mi

Dispersion Curves

• Start with seismogram amplitudes relative to distance and time: (x-t). • p-t transform (simple line integral across the seismic record A(x, t)). • Discrete form of the p-t transform (in practice). • Take each A(p-t) trace and compute its FFT. • Power spectrum • Forward and reverse directions