Seismic reflection data acquistion in Central Volcanic Region : problems associated with the near-surface

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Bannister, S.C. 1993 Seismic reflection data acquistion in Central Volcanic Region : problems associated with the near-surface. Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 93/01 33 p.


Abstract: Experimental seismic trials were carried out near the Mokai geothermal field in a continuing effort to improve the signal to noise ratio of seismic reflection data collected in the Central Volcanic Region. Elastic parameters of the near surface layer were determined as well as the effect of acquisition parameters, in particular, shot and receiver depth, on seismic data quality. High seismic attenuation is evident in the top 6 to 9m of the surface layer, as is a large increase in P velocity which is likely to be associated with 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 efficient waveguide for surface waves. (auth)