Abstract: A geophone configuration is disclosed that includes an elongated extension or spike that couples with the soil in the hole made by the spike in the region near the end of the spike without hard or firm coupling with the soil above that region. A bow spring or drill bit larger in diameter than the diameter of the spike can be used for achieving predominant contact for the coupled region compared to soil opposite the remainder of the spike. Alternately, a weighted tip can be employed to achieve relative superior coupling by weight compared with the less heavy region of the spike above such weighted tip.

Abstract: A low noise, magnetotelluric, intercalation electrode is disclosed that is both electronically and ionically conductive and stable in ground water brine. The electrode is comprised of an inert or chemically inactive long cylindrical and porous support shield, a semipermeable membrane located in the shield selectively permeable to the positive ions of a metal selected from the group consisting of Na+ and K+ ions, a brine electrolyte, and an electrode axis located in the brine electrolyte that includes an electronically conductive, metallic material ionically reversible to Na+ and K+. The electrode is sealed and attachable at its electrode axis to a wire leading to another electrode spaced apart therefrom. The wire connection permits voltage measurements and thereby provides a method for determining the resistivity between the electrodes at frequencies that are quite low without being interferred with by noise attendant prior art magnetotelluric electrodes.

Abstract: There is disclosed a device for shoring the side walls of a trench or the like which includes a pair of elongate rails and a pair of parallel, hydraulically extendible and contractible actuators connected at opposite ends to the rails for lowering with the rails into and out of positions between the walls of the trench, and adapted, when extended, to hold the rails tightly against the walls.