An Unbiased Spiral Array for MASW: a Step Towards 3D Survey

The MASW surveys are typically carried out with linear geophone arrays and the current MASW algorithm also assumes the geophones arranged with an equal distance. To expand the MASW technique to 3D as in the 3D reflection surveys, two issues have to be overcome: multiple azimuth and variable source-receiver offsets. This study tackles the first issue of feasibility of MASW to a seismic record collected in multiple azimuths. First, the possible geometrical bias of a linear array is examined. This is a question of where in the linear array the analysis result should be attributed to. Experimental MASW processing of seismic data suggests it is not always the middle of the geophone array. There appears to be some geometrical bias. A spiral array is devised to experiment multiple azimuths maintaining the constant increment of the source-receiver offset to analyse so that conventional MASW software can be used. As the source point is at the centre of the array, no geometrical bias is considered present. The result demonstrated that seismic data with multiple-azimuth can be used for MASW analysis provided with a constant source-receiver increment. This restriction is a subject of next step of 3D MASW processing.