An extended MSPAC method in circular arrays

Abstract : The microtremor seismic method using spatial autocorrelation (SPAC) processing is a useful tool for estimating the structure of subsurface layers and the shear wave velocities of sediments. This paper improves upon the well-known 'Modified SPAC' (MSPAC) method, which extends the SPAC formulae for discrete and nearly continuous circular arrays to handle arrays with regular and irregular azimuthal spacing. For finite circular arrays, extended MSPAC (EMSPAC) also takes into account the discrete character of the array, which has been inspired by the works of Okada. Also a new SPAC coefficient is proposed for a nearly continuous array. EMSPAC is applied to real data collected using a seven-station array, and its averaged SPAC coefficients and dispersion curves are compared to those obtained using MSPAC.