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Method
Pioneer works for determining velocity structure by using microtremors or microseisms were
carried out by Aki (1957), Toksoz (1964), and Lacoss et al. (1969). The methods are provided for
estimating velocity structures by using the phase velocity dispersion of surface waves included in
microtremors. Asten and Henstridge (1984), Horike (1985) , and Matsushima and Okada (1990)
made efforts to increase the resolution of phase velocity determination by using array
observation of microtremors, applying the frequency-wavenumber (f-k) analysis (Capon, 1969).
Horike (1985) developed also an inversion method of obtained phase velocity of Rayleigh waves
for determining S-wave velocity structure. Aki (1957) gave a theoretical basis of the spa tial
autocorrelation coefficient defined for microtremors data and developed a method to estimate
phase velocity dispersion of surface waves contained in microtremors by using a specially
designed circular array. Henstridge (1979) also introduced a licit expression of a relationship
between the spatial autocorrelation coefficient and the phase velocity of fundamental-mode
Rayleigh waves. The method has been extended to an exploration method by Okada et al. (1990),
Matsuoka et al. (1996), and Okada (1998), that is currently called SPAC method. The SPAC
method has been employed throughout the present study. A flow of observation and analysis in
the method is shown in Figure 1, and a principle of the method is given in Appendix.
da: Site Specific Issues on Strong Ground Motion during the Kocaeli, Turkey
Earthquake of August 17, 1999, as Inferred from Array Observations of Microtremors and ftershocks
by
Kazuyoshi Kudo, Tatsuo Kanno, Hiroshi Okada, Oguz Özel, Mustafa Erdik,
Masayoshi Takahashi, Tsutomu Sasatani, Sadanori Higashi, and Kunikazu Yoshida
