The 2012 Newcastle and Sydney SPAC surveys

Theodora Volti; Clive Collins; Michael Asten

doi:10.1071/ASEG2013ab316

ISSN: 2202-0586
E-ISSN:

oa The 2012 Newcastle and Sydney SPAC surveys
Authors Theodora Volti^a, Clive Collins^b and Michael Asten^c
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^a Geoscience Australia, PO Box 378, ACT, 2601, [email protected] ^b Geoscience Australia, PO Box 378, ACT, 2601, [email protected] ^c Monash University, Victoria, 3800, [email protected]
Publisher: Australian Society of Exploration Geophysicists
Source: ASEG Extended Abstracts, Volume 2013, Issue ASEG2013 - 23rd Geophysical Conference, Dec 2013, p. 1 - 6
DOI: https://doi.org/10.1071/ASEG2013ab316
- Published online: 01 Dec 2013

Abstract

Since the 1989 Newcastle ML5.5 earthquake, the city of Newcastle, Australia, has become a focus for earthquake risk assessment. Surficial geology in the area varies from deeper alluvial deposits near the Hunter River, to shallower soils overlying weathered rock on the valley margins. Ambient vibration techniques, based on the dispersion property of surface waves in layered media, are promising for assessing the subsurface geophysical structure, in particular the shear-wave velocity (Vs). Using one such technique, the Spatial Auto-Correlation (SPAC) method, we characterise soil deposits at 23 sites in and around the city of Newcastle. Results show that values for soil overlying bedrock ranges from 200 m/s to 1000 m/s, with the higher velocity values observed in shallow soils which are relatively consolidated and distal to the river. Bedrock depth varies from 6 to 56 m, but an accurate quantification is hampered by the low frequency picks (< 2 Hz) which are either unavailable or of dubious quality. Some Vs profiles show two abrupt changes, the first at ~ 4-15 m depth and the second ~19-56 m. Low Vs values are of particular interest as they may indicate areas of higher seismic hazard.

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References

Asten, M.W., 2006, Site shear velocity profile interpretation from microtremor array data by direct fitting of SPAC curves: Proceedings of the Third International Symposium on the Effects of Surface Geology on Seismic Motion (ESG2006), Grenoble, France, 30 August - 1 September 2006, vol. 1, Paper Number: 99.
Asten, M.W., 2012. Newcastle-Sydney SPAC microtremor survey project 2012: velocity models and H/V spectra. Monash University Report.
Bettig B., Bard, P. Y., Scherbaum, F., Riepl, J., Cotton, F., Cornou, C. and Hatzfeld, D. (2001). Analysis of dense array noise measurements using the modified spatial auto- correlation method (SPAC): applications to the Grenoble area. Bolletino di Geofisica Teoroca ed Applicata 42, 281-304.
Dhu T. and Jones, T., 2002. earthquake Risk in Newcastle and Lake Macquarie. Record 2002/15.
Nakamura, Y. (1989). A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface, Quality report of RTRI. Railway Technical Research Institute/Tetsudo Gijutsu Kenkyujo, Japan, pp: 25-33.
Kayen R., Carkin, B., Allen, T., Collins C., McPherson, A. and Diane Minasian, 2013. Seismic-Shear Wave Velocity and Ground Motion Amplification Factors for 50 Australian Site determined by the Spectral Analysis of Surface Waves. USGS Report Series 2013-(in prep.)
Sambridge, M, 1999a. Geophysical Inversion with a Neighbourhood Algorithm -I. Searching a parameter space, Geophysical Journal International, 138 , 479-494, 1999.
Sambridge, M., 1999b. Geophysical Inversion with a Neighbourhood Algorithm -II. Appraising the ensemble, Geophysical Journal International, 138, 727-746, 1999.
Sorensen, C. and Asten, 2005. Comparison of shear-wave velocity profiles of Quaternary sediments in the Newcastle area estimated from SCPT, microtremor spectral ratios and array studies, and drilling. Earthquake Engineering in Australia, proceedings of the Australian Earthquake Engineering Society, Albury Victoria, Paper 9.
Wathelet, M., D. Jongmans, and M. Ohrnberger , 2005. Direct Inversion of Spatial Autocorrelation Curves with the Neighborhood Algorithm. Bulletin of the Seismological Society of America, 95, 1787-1800.
Wathelet, M., 2008. An improved neighborhood algorithm: parameter conditions and dynamic scaling. Geophysical Research Letters, 35, L09301, doi:10.1029/2008GL033256.

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Article Type: Research Article

Keyword(s): site response; SPAC; Vs30

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