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were used in all field experiments requiring velocity transducers. The 4.5-Hz geophones
purchased from Geospace LP, shown in Figure 3.26, are constructed using a rotating dual
coil design which is more durable in rough handling conditions than single coil designs.
The model number GS-11D geophones are cased in model 902 marsh cases from
Geospace. The marsh cases include a double o-ring seal and a rubber neck strain relief
system making them water resistant. They can also be fitted with a spike for on-land
testing applications or an aluminum disk for pavement and other hard surface
applications.
Geophones were assembled from the case components seen in Figure 3.26.
Pigtail wires were installed on the geophones for on-land use. An assembled geophone
used in on-land testing is shown in Figure 3.27.
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