GFA BOREHOLE 3D GEOPHONE for downhole/crosshole

    seismic > downhole, crosshole, vs30

Borehole 3D Geophone Mod. GFA 50/100 is designed for seismic borehole testing according to ASTM D7400-08 (downhole) and ASTM D4428 (crosshole). It is based on 3x high-sensitivity sensor elements (nat.freq.10 Hz - 1 vertical and 2 horizontal sensors), oriented according to a triad of orthogonal Cartesian axes XYZ. Supplied with a cleat assembly to sustain its weight at the requested depth (GFA cable is graduated in meters), this borehole geophone has a pneumatic-mechanical clamping system with lateral lever and spacer block. Simply connect the pump to the GFA panel to operate: pumping air at a pressure of 2-3 bar, you will achieve excellent sensor coupling to the borehole wall (diameter between 50 and 110mm for use with the standard spacers). GFA is lightweight and easy to transport; the anodised aluminium casing makes it suitable for use on-site and easy to maintain. Moreover, two GFA can be connected one under the other by means of a special spacer accessory.

Available in two versions: GFA-50 with 50m of cable and GFA-100 with 100m of cable.


Number of geophones: 3 geophones with natural freq. 10Hz+/-5% (1 vert.+ 2 horiz.), high-sensitivity (100V/m/sec +/-5%) 

Cable length: 50m or 100m, graduation in metres, mounted on cable reel with probe support 

Probe dimensions: Ø51mm, length 570mm (anodised aluminium casing)

Borehole diameter: Min. 55mm, max. 110mm (with standard spacer block; larger diameters upon request)

Cable reel dimensions: 540x400x250mm 

Weight: GFA-50: <12kg; GFA-100: <17kg 

Seismograph connection: Standard: Cannon type NK2721C (GEA24, 16SN-U-P) or Souriau (GEA3, Anteo), Other adapters available upon request