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Operative guide masw MASW OPERATIVE GUIDE MASW SEISMIC MAE advanced geophysics instruments - www mae-srl it CMASW MASW surface seismic procedure General Geophysics exploration with surface waves allows to get S waves propagation velocity into the ground i

MASW OPERATIVE GUIDE MASW SEISMIC MAE advanced geophysics instruments - www mae-srl it CMASW MASW surface seismic procedure General Geophysics exploration with surface waves allows to get S waves propagation velocity into the ground in a simple and less expensive way MASW method Multichannel Analysis of Surface Waves allows to determine Vs speed pro ?le overcoming some limits of refraction method such as velocity inversion A limit to its application can be presence of signi ?cant slopes both of topography than di ?erent elastic discontinuities Survey does not require long time of acquisition and provides good results also in presence of noise Rayleigh waves in a strati ?ed means are dispersive propagating with di ?erent velocities and group velocities they are registered along geophones array after arti ?cial energization and then are analyzed through complex computing techniques based on recognition of soil multi-layer models Although signal generated by a vertical point source generates also P and SV waves Rayleigh waves contribution predominates because they carry about of generated energy and because they are subject to lower geometric attenuation compared to P and S waves given that they propagate according to spherical wave directions S waves analysis through MASW method is performed through spectral processing of seismogram after Fourier transformed which provides signal spectrum In this domain named transformed domain signal related to S waves is distinguished by other signals such as P waves or air waves Observing frequency spectrum it is possible to notice that S wave propagates at variable speed according to its frequency as a result of dispersion phenomenon Once performed picking on f-K spectrum or on dispersion curve obtained by ?eld data through inversion process it is possible to get speed pro ?le with depth that allows to de ?ne Vs parameter Generally active method allows to get phase velocity dispersion curve within frequency range of - Hz and - Hz The whole process includes three subsequent steps a recording of ?eld data of surface waves ??ground roll ? b generating a dispersion curve graphic of phase velocity compared to frequency c inversion of dispersion curve to get Vs vertical pro ?le MAE advanced geophysics instruments - www mae-srl it CMASW Inversion of dispersion curve is then iteratively realized using experimental dispersion curve as reference both for direct modeling and for minimum square procedure Recording modality Proper instruments shall be made of at least following components - channels digital seismograph better if channels with recording stack possibility signal gain in amplitude and minimum bit dynamic of A D converter - for soil characterization tests better if vertical geophones with frequency equal or lower than Hz - energization system to be chosen according to survey scale usually an hammer with plate on the ground oleo-pneumatic and or gravity pulses seismic energizers vibrating sources vibrodyne or seismic ri es can be also used - metric rib for a correct positioning of receivers Recording targets are to provide data related to surface waves propagation in a frequency band as much