Vertical seismic profiling (VSP) is a borehole geophysical method. Geophones in the borehole record reflected seismic energy from a seismic source at the surface. Data obtained from a Vertical Seismic Profiling survey will provide different geophone depths is used to calculate a detailed seismic velocity profile of the subsurface in the immediate vicinity of the test borehole.
The seismic source used is typically a wooden beam and steel plate laid on the ground in close proximity to the borehole. The beam is struck with a sledge hammer on alternate ends of the beam to induce polarized shear waves. A three component borehole geophone is used to measure the compression and shear wave shots.
The three components (vertical, longitudinal, and transverse) of the recorded data are analyzed individually and split into depth-wave trains. P- and s-wave arrivals are then picked and are best fit to a model to determine layer thicknesses and compression and shear wave velocities near the borehole.
The results of a Vertical Seismic Profiling (VSP) survey are often used for earthquake engineering site classification, as per the National Building Code of Canada, 2010.
Values for Poisson’s ratio (ν), shear modulus (G), Young’s modulus (E) and Bulk Modulus (K) are calculated from compression wave and shear wave velocities as:
Where ρ is the bulk density (in Kg/m3), VP is the compression wave velocity (m/s) and VS is the shear wave velocity (m/s).