The use of wavenumber normalization in computing spatially averaged coherencies (krSPAC) of microtremor data from asymmetric arrays

M W Asten, W J Stephenson, S Hartzell

Research output: Chapter in Book/Report/Conference proceedingConference PaperResearchpeer-review

Abstract

The spatially-averaged coherency (SPAC) method of processing microtremor noise observations for estimation of Vs profiles requires a circular or triangular array symmetry in order to allow spatial (azimuthal) averaging of inter-station coherencies over a constant station separation. Common processing methods allow for station separations to vary by typically ±10% in the azimuthal averaging before degradation of the SPAC spectrum is excessive. In this paper we develop a new wavenumber-normalised SPAC method (krSPAC). The traditional analysis of SPAC data involves performing averaging of sets of coherency versus frequency spectra and then fitting to a model SPAC spectrum. In our new approach we interpolate each spectrum to coherency versus kr, where k and r are wavenumber and station separation respectively, and r may be significantly different for each pair of stations. The averaging and interpolation changes with each iteration of velocity models, since k is a function of frequency and phase velocity and thus is updated each iteration. The method proves robust and is compared with alternative methodologies using asymmetric arrays in the Santa Clara Valley CA, Pleasanton CA, and Seattle WA, where station spacings are irregular and vary from 300m to 2000m.
Original languageEnglish
Title of host publication6th International Conference on Earthquake Geotechnical Engineering (6ICEGE)
EditorsBrendon Bradley
Place of PublicationChristchurch New Zealand
PublisherThe Conference Company
Pages1-9
Number of pages9
Publication statusPublished - 2015
EventInternational Conference on Earthquake Geotechnical Engineering (ICEGE 2015) - Christchurch, New Zealand
Duration: 1 Nov 20154 Nov 2015
Conference number: 6th
http://www.6icege.com/

Conference

ConferenceInternational Conference on Earthquake Geotechnical Engineering (ICEGE 2015)
Abbreviated titleICEGE
CountryNew Zealand
CityChristchurch
Period1/11/154/11/15
Internet address

Keywords

  • Analogue experiments
  • Draw-up height
  • Intrusion-hosted deposits
  • Mafic magma
  • Magma volumetric flow rates
  • Ni-Cu-PGE deposits

Cite this

Asten, M. W., Stephenson, W. J., & Hartzell, S. (2015). The use of wavenumber normalization in computing spatially averaged coherencies (krSPAC) of microtremor data from asymmetric arrays. In B. Bradley (Ed.), 6th International Conference on Earthquake Geotechnical Engineering (6ICEGE) (pp. 1-9). The Conference Company.