MICROTREMOR COHERENCY: SIMULTANEOUS RECORDING WITH ARRAYS HAVING DIFFERENT APERTURES

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.