| Abstract |
In an effort to improve the signal to noise ratio of seismic reflection data collected in the Central Volcanic Region, experimental seismic trials have been carried out near the Mokai geothermal field. The nature of the complex seismic wave propagation in the near surface Sayers was examined and the noise field characterised. We determined the elastic parameters of the near surface layer as well as variation of the seismic data quality with acquisition parameters, in particular, shot and receiver depth. High seismic attenuation is evident in the top 6 to 9m of the surface layer, as is a large P velocity contrast which is likely to be associatedwith the degree of water saturation. This velocity structure results in reverberation of P-wave refracted arrivals and substantial P-to S wave conversion. Changes in the shear wave velocity, probably related to changes in porosity, form what is in effect a very efficientwaveguide for surface waves. |