Microtremor coherency

Simultaneous recording with arrays having different apertures

Authors

  • W. R. Stephenson GNS Science, Lower Hutt, New Zealand

DOI:

https://doi.org/10.5459/bnzsee.43.1.1-6

Abstract

By recording microtremors simultaneously using arrays having two apertures, the effect of incoherent noise, which can act to depress coherency values, may be reduced, leading to better estimates of azimuthally-averaged coherency, and hence to improved shear-wave velocity profiles at sites. The method is exemplified by the use of 30 m and 40 m triangular arrays at McEwan Park, Lower Hutt, New Zealand, where the method is shown to result in better fits to theoretical coherency. Adequate correction is confined to low frequencies (less than 4.5 Hz in this case). Estimates of Vs are modified for greater depths (50 to 200m in this example) but unaltered for near-surface materials.

References

Roberts, J.C. and Asten, M.W., (2005) “Estimating the shear velocity profile of Quaternary silts using microtremor array (SPAC) measurements” Exploration Geophysics (Melbourne), Vol. 36, no. 1, pp.34-40 DOI: https://doi.org/10.1071/EG05034

Chávez-García, F. J., Rodríguez, M., Stephenson, W. R. (2004) “Site effects and SPAC; results for three sites in Wainuiomata” Bulletin of the New Zealand National Society for Earthquake Engineering, Vol. 37, no. 3, pp.101-110 DOI: https://doi.org/10.5459/bnzsee.37.3.101-110

Asten, M.W., Dhu, T., and Lam, N. (2004) “Optimised array design for microtremor array studies applied to site classification; observations, results and future use”: Paper 2903, Conference Proceedings of the 13th World Conference of Earthquake Engineering, Vancouver, Aug 1-6, 2004

Roberts, J.C. and Asten, M.W. (2008) “A study of near source effects in array-based (SPAC) microtremor surveys” Geophysical Journal International 174(1):159-177. DOI: https://doi.org/10.1111/j.1365-246X.2008.03729.x

Cho, I., Tada, T. and Shinozaki, Y. (2008) “Assessing the applicability of the spatial autocorrelation method: A theoretical approach” Journal of Geophysical Research 113(B6):B06307. DOI: https://doi.org/10.1029/2007JB005245

Tagare, P. (1993) “Signal averaging” Chapter 9 of Tompkins, W. Biomedical digital signal processing, Prentice-Hall.

Cho, I., Tada, T. and Shinozaki, Y. (2007) “Beyond the SPAC Method: Exploiting the Wealth of Circular-Array Methods for Microtremor Exploration” Bulletin of the Seismological Society of America, 97(6):2080–2095. DOI: https://doi.org/10.1785/0120070058

Asten, M. W., Stephenson, W.R., and Davenport, P. N. (2005) “Shear-wave Velocity Profile for Holocene Sediments Measured from Microtremor Array Studies, SCPT, and Seismic Refraction” Journal of Environmental & Engineering Geophysics 10(3): 235 – 242. DOI: https://doi.org/10.2113/JEEG10.3.235

Herrmann, R.B. (2001) “Computer programs in seismology - an overview of synthetic seismogram computation Version 3.1: Department of Earth and Planetary Sciences, St Louis Univ.

Asten, M.W. and Boore, D.M. (2005) “Comparison of shear-velocity profiles of unconsolidated sediments near the Coyote borehole (CCOC) measured with fourteen invasive and non-invasive methods, in Asten, M.W. and Boore, D.M., eds., Blind comparisons of shear-wave velocities at closely spaced sites in San Jose, California: U.S. Geological Survey Open-File Report 2005-1169. DOI: https://doi.org/10.2113/JEEG10.2.85

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Published

31-03-2010

How to Cite

Stephenson, W. R. (2010). Microtremor coherency: Simultaneous recording with arrays having different apertures. Bulletin of the New Zealand Society for Earthquake Engineering, 43(1), 1–6. https://doi.org/10.5459/bnzsee.43.1.1-6

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