Abstract: A method of detecting precursor seismic electromagnetic waveforms and predicting future seismic activity in the form of an earthquake by placing a detector including a dielectric material in contact with the earth. The detector receives at the dielectric material precursor seismic electromagnetic waveforms traveling within the earth emanating from a region of seismic activity. A sensor responsive to the dielectric material senses a series of individual discrete signals imposed by the waveforms at the dielectric material wherein each of the signals has the characteristic of a rise time that is shorter than its fall time. Alternatively, the discrete signals may be a single discrete signal characterized by a plurality of overlapping waveforms. Then predicting based on the series of the signals the occurrence of the earthquake.

Abstract: A sensor element especially adapted for use in borehole resistivity logging, having an outside surface comprising conductive portions and insulating portions distributed in a determined pattern, said conductive and insulating portions being made respectively of a material that is hard and electrically conductive and of a material that is hard and electrically insulating, each of said materials being deposited in the form of a layer.

Abstract: A real time soil constituent sensor and precision agricultural chemical delivery system may measure simple in situ soil constituents without the aid of externally applied solvents, or such solvents may be utilized intermittently to calibrate the measurements for greater accuracy. A real time complex in situ soil resistivity sensor and prescription agricultural chemical delivery system includes a plurality of ground-engaging tools in association with individual soil electrode arrays which measure complex solute and matrix resistivity levels. Conventional ground-engaging tools may serve as electrodes for impressing a voltage source and serve as a current sink for the purposes of determining complex resistivity values and components thereof in in situ soils. Alternatively, local resistivity measurements in a single tool can also be employed for separation of resistivity contributions of the soil solute and the matrix.

Abstract: The invention is an electrical logging system for determining the electrical resistivity of a subsurface formation from a cased borehole that may include voltage and current supply means, voltage and current control means, electrode support means, and voltage and current processing means. In particular, the system also may include a first pair of electrodes, current electrodes, and a second pair of electrodes, voltage electrodes. The current electrodes are adapted to be electrically connected at different heights to the casing within the borehole and nearby one of the ends of the borehole for supplying an electrical current to the casing. The space between the current electrodes defines an intermediate casing part through which casing current flows. The casing current flowing through the intermediate casing part causes the casing part below the intermediate casing part to have a different electrical potential than the casing part above the intermediate casing part.

Abstract: The measurement equipment serves to map the subsurface geology in a terrain by means of electrical profiling. A plurality of drag electrodes are used for this purpose, the electrodes with specific mutual spacing, being hooked together with a tow in the form of, e.g., a rope or a wire which is towed by a towing means. An electrical current which is so low as to constitute no danger to operators, is transmitted into the earth through the current electrodes and the voltage is measured across the voltage electrodes. A single-ended electrode amplifier is incorporated into each of the voltage electrodes. The method is useful for rapid and detailed mapping of deposits of natural resources, moist site areas, sand and clay localities in connection with road construction and building land as well as water magazines and refuse dumps.

Abstract: The invention concern a combination well logging device adapted to be moved inside a borehole to measure the properties of geological formations through which the borehole passes.The device according to the invention comprises a series of elongate logging sections mounted end to end, including a first section adapted to be maintained with a generatrix applied against the wall of the borehole, a second section comprising a body and a measurement pad adapted to be spaced radially from the body for application against said wall, a third section adapted to be kept space from said wall, and first and second hinges connecting the second section to the first and third sections respectively in order to allow respective angles of inclination between the second section and the first and third sections.

Abstract: A method and apparatus for estimating the earth's resistance (conductivity) as a function of depth using electroseismic prospecting (ESP) or inverse ESP techniques. Resistance is determined by the frequency-dependent attenuation of reflected EM signals which are produced by application of seismic signals to the earth. A seismic wave is generated by conventional means into the earth, and EM waves are generated back to the surface by different reflectors at different depth levels. This propagation attenuates the high frequencies preferentially. EM waves generated at lower depths are further attenuated relative to those waves generated at more shallow depths. The method and apparatus determines the difference in spectral content between the reflected signals from different horizons based on their relative attenuation and uses this difference as a direct measure of the conductivity between the horizons.

Abstract: A soil electrode assembly supports an electrode member disposed in soil in front of another electrode member so that a resistivity of a volume of the soil that is between the electrode members is measured by energizing and monitoring the electrode members. The soil electrode assembly includes a substantially flat support member having two principal opposite faces and a lower end drivable into the soil. The support member is made of rigid material. One of the faces of the support member includes a first opening providing an access to a first compartment. The soil electrode assembly also includes a substantially flat insulating member having two principal opposite faces. The insulating member is mounted in the first compartment. One of the faces of the insulating member includes a second opening providing an access to a second compartment. An electrode member is mounted in the second compartment.

Abstract: The present invention relates to a method and apparatus for measuring current resulting from a magnetic field source (i.e., a transmitter) positioned on a drill collar. A plurality of current detectors are carried on the surface of the drill collar in an insulated relationship thereto. Each of the detectors is positioned to detect the value of current being received by the same from the formation. In this connection, the detectors are positioned at differing longitudinally displaced positions relative to the axis of the drill collar and the transmitting antenna(s), whereby each detects a different value of current. These currents will respectively flow through successively deeper layers of the formation. The longitudinal displacement is directly proportional to the depth of investigation, whereby the depth of investigation is many times the longitudinal distance between the current detector and the corresponding transmitting antenna.

Abstract: A method for producing electrochemical impedance spectra. Spontaneously occuring coupling current noise between an array of electrodes which may be of substantially the same material is detected. A time domain record of the detected current noise is stored and the time domain record of the detected current noise is transformed to the frequency domain. Spontaneously occurring potential noise between the array of electrodes and a further electrode is detected. A time domain record of the detected potential noise is stored and the time domain record of the detected potential noise is transformed to the frequency domain. The frequency domain current noise and potential noise transformations are then transformed to the impedance domain to produce the required electrochemical impedance spectra.

Abstract: Process and apparatus for determination of permeability of porous media by measurement at finite frequency of streaming potential and electro-osmotic induced voltage and pressure due to applied finite frequency pressure oscillations and alternating current, respectively. The inter-electrode distance between points of application and measurement of the alternating signals at a finite frequency is small compared to the wavelength of the pressure oscillations and alternating current voltage.

Abstract: Measurement-while-drilling apparatus is disclosed for determining the resistivity of formations surrounding an earth borehole. An electrically conductive metal body, such as a drill collar on a drill string, is movable through the borehole. A transmitting toroidal coil antenna is disposed on the body and is energized to induce a current which travels in a path that includes the body and the formations. An electrode is disposed on the body, and an electrical signal resulting from said current is measured at the electrode to obtain an indication of the resistivity of the formations. In a disclosed embodiment, one or more electrodes can be mounted on a blade that is mechanically coupled to the body.

Abstract: A portable underwater mount for magnetic and electric field sensors. The mount has a gimbal-like structure comprising a ball member having a mounting flange for coupling to the magnetometer. The ball member is cast from polyurethane with Teflon powder suspended therein, providing a substantially frictionless surface. The ball member is disposed over a support platform having a spherical contour so that the weighted sensor positions itself to true vertical. A collar having a lock terminating in the support platform rests over the ball member so that once the sensor is oriented to magnetic north, the lock is engaged to secure the sensor in true vertical and magnetic north positions.

Abstract: The method and apparatus relies on a modified induction approach and preferably is incorporated into a metal drill collar for MWD measurements. A primary changing magnetic field is formed in a formation by a transmitting antenna which is in a groove on the surface of a drilling collar. Such drill collar also carries a plurality of detecting antennas and/or current detectors which detect the value of current induced in the formation to provide a resistivity profile immediately adjacent the borehole. An embodiment uses a hybrid modified induction and electrical approach.

Abstract: A disclosed embodiment utilizes one or more toroidal coil antennas mounted, in an insulating medium, on a drill collar to induce currents which travel in a path that includes the drill collar and earth formations around the drill collar. At least one array of electrodes is provided on at least one stabilizer blade of the drill collar and is utilized to detect currents transmitted by toroidal coil antennas which return via the formations to the electrodes laterally; that is, approximately normal to the axis of the drill collar. Signal traces are obtained from measurements taken at respective ones of the transducers, and a dip characteristic of the formations is determined from the signal traces and from signals representing the rotational orientation of the drill collar.

Abstract: An electrode for use in the electrical investigation of a medium such as a borehole wall, comprises a sheet (32) of electrically resistive material having opposed first (34) and second (33) surfaces, one or more elongate electrical conductors (35,36) of low resistivity, an end face of each conductor abutting the first surface of the sheet (32) and means for sensing electric current passing through each conductor. In use, the second surface (33) of the sheet (32) is exposed to the medium to be investigated.

Abstract: A real time soil chemical sensor and precision agricultural chemical delivery system includes a plurality of ground-engaging tools in association with individual soil sensors which measure soil chemical levels. The system includes the addition of a solvent which rapidly saturates the soil/tool interface to form a conductive solution of chemicals leached from the soil. A multivalent electrode, positioned within a multivalent frame of the ground-engaging tool, applies a voltage or impresses a current between the electrode and the tool frame. A real-time soil chemical sensor and controller senses the electrochemical reaction resulting from the application of the voltage or current to the leachate, measures it by resistivity methods, and compares it against pre-set resistivity levels for substances leached by the solvent. Still greater precision is obtained by calibrating for the secondary current impressed through solvent-less soil.

Abstract: The present invention relates to a device and method for using a logging probe of small diameter with resect to a well in which it is to operate. The device of the invention is characterized in that it includes a widener for widening the diameter of said probe.

Abstract: A method for reducing impulsive noise in electromagnetic geophysical data utilizes a receiving antenna and one or more noise sensors. The type of noise sensor used depends on the type of impulsive noise which is to be monitored. Motion noise is monitored with a tilt meter or similar motion sensor. Impulsive electromagnetic noise is monitored with an electric or magnetic field sensor which is located so as to receive impulsive noise while minimizing the reception of the electromagnetic signal of interest. Impulsive noise is monitored without the electromagnetic signal of interest for a short period of time to enable the determination of a threshold noise value. Then, the impulsive noise is monitored simultaneously with the electromagnetic signal of interest, wherein the impulsive noise is received by the noise sensor and the signal of interest is received by the receiving antenna.

Abstract: The present invention relates to a device and method for using a logging probe of small diameter with respect to a well in which it is to operate. The device of the invention is characterized in that it includes a widener for widening the diameter of said probe.

Abstract: A sonde has an at least approximately cylindrical drill-stem member, whereby the drill-stem member may be coupled with other drill-stem members into a drill string. A spiral winding is longitudinally about the drill-stem member for conveying drilled out earth up to a surface of the earth when the drill-stem member is rotated into the earth, whereby the drill-stem member is an auger. At least one longitudinal surface portion of the drill-stem member is an electrical insulator that extends inwardly of the surface portion at least part of a radius of the drill-stem member. At least one measuring electrode is embedded in the electrical insulator. A connecting arrangement is in the drill-stem member for connecting the measuring electrode to electric operation and measuring equipment, whereby the auger is also an electrically logging sonde.

Abstract: A method of electroseismic prospecting is disclosed for detecting either the presence of two immiscible fluids present in a porous subterranean formation or the presence of a high-permeability rock formation including a substantially aqueous phase therein. A seismic impact produces an acoustical wavefront that results in an enhanced electromagnetic signal when it encounters either types of the above-described formations. This resulting enhanced electromagnetic signal is detectable as an indication of a likely hydrocarbon deposit, thereby giving additional data information with conventional seismic data to the geophysical prospector.

Abstract: A sample accommodator for the measurement of dielectric properties includes a conductive strip having two planar surfaces, and two ground planes, one parallel to each of the planar surfaces of the conductive strip. At each end, the strip passes through but is electrically isolated from an endplate which is electrically and physically connected to each ground plane and which maintains the relative positions of the ground planes. Dielectric properties are measured by placing a sample between each face of the strip and the ground plane parallel to it.

Abstract: In order to increase the angular field of observation of a logging sonde usable, in particular for dip metering, the sonde is equipped with measuring pads each comprising two independent flaps. The flaps of the same pad are hinged to a central element which is held permanently parallel to the axis of the sonde body, and they are applied against the wall of a borehole by blade springs. Each of the flaps carries an array of electrodes. The flaps of each of the measuring pads are circumferentially offset relative to each other so that the angular field of observation is increased without increasing the diameter of the sonde, once the pads have been retracted.

Abstract: The present invention relates generally to a method of geophysical exploration and more particularly to a novel method of magnetotelluric exploration. In one embodiment, a series of continuous electric dipole measurements of one component of the earth's electric field are obtained along a zigzag line. Concurrently, at least two components of the earth's magnetic field are obtained in the vicinity of the zigzag line. Each electric dipole measurement of the earth's electric field comprise measures of the potential difference between electrodes spaced along the zigzag line in which the included angle between adjacent pairs of electric dipole measurements is less than 180.degree.. Preferably, the included angle between adjacent electric dipole measurements is between 90.degree. and 150.degree..

Abstract: Process for in situ recovery of carbonaceous values from underground petroleum impregnated media such as oil shale, under controlled radiation from a microwave distributing source adjacent the media, e.g. in a borehole, effected in the absence of air, such that the radiation is distributed at least initially at incrementally increasing power and/or at least initially in intermittent interval cycles of on and off duration of the microwaves, for selective pyrolysis of the organic content of the media to liquid, vapor and gas form as the case may be under autogenous pressure in the pores of the media for driving the organic constituents therefrom for appropriate recovery, e.g. via the borehole, including breakup of larger molecules, e.g.

Abstract: A resistivity surveying apparatus comprises a base station (9) and 30 reels (RL1 to RL30). The base station (9) comprises a computer (10) and a resistivity meter (11) having four output terminals. Each reel has a multi-line cable (CB1 to CB30) which includes four resistivity measuring lines for connection to the output terminals of meter (11) and further lines for connection to the output terminals of computer (10). An electrode (EL1 to EL30) which may be driven into the ground is mounted on each reel. In the hub of each reel (RL1 to RL30), there is provided a circuit (CKT1 to CKT30) for connecting the electrode (EL1 to EL30) to one of the resistivity measuring lines under the control of the computer (10). In operation, the electrodes are driven into the ground at spaced intervals. The free end of one (CB1) of the cables is connected to the base station (9) and the remaining cables are connected in series. The computer (10) then drives the apparatus through a measurement sequence.

Abstract: A cable connection head is disclosed, in which a well logging cable is inserted through an upper head housing of a head housing consisting of a lower head housing coupled to an upper portion of a measuring instrument housing and the upper head housing coupled to an upper portion of the lower head housing, armoring wires of the well logging cable secured to the upper head housing, and core wires of the well logging cable are connected to a connector which is fittedly secured to the lower head housing. A metal covered cable of the well logging cable is constructed by accommodating a plurality of core wires and filling with an electric insulating material in a metal tube. The lower head housing and metal covered cable are reliably sealed to each other such as to be able to withstand high temperature by inserting the metal tube of the metal covered cable through the lower head housing and securing the metal tube by means of welding around the entire outer periphery to the top of the lower head housing.

Abstract: The response characteristics of a combination of hole-centered electric logging tools in a variety of borehole conditions can be obtained by means of impedance values as entries of a matrix resulting from measurements over a series of depth increments, utilizing an array of M electrode assemblies of equal incremental spacing positioned on a rigid mandrel. While the array is substantially stationary within the borehole, currents from ech electrode are emitted independently, one at a time, allowing the impedance matrix to be formed by the principle of linear superposition in terms of voltage and voltage difference measurements between adjacent electrodes; the impedance matrix is inverted and used to generate a set of tool responses, which when properly compared to a set of tool responses previously generated by computer simulation and addressable by sets of borehole parameters and calibration factors, allows the corresponding borehole conditions to be deduced from the measured data.

Abstract: The response characteristics of a combination of hole-centered electric logging tools in a variety of borehole conditions can be obtained by means of impedance values as entries of a matrix resulting from measurements over a series of depth increments, utilizing an array of 2M-1 electrode assemblies of equal incremental spacing positioned on a rigid mandrel. While the array moves continuously along the borehole, current is continuously emitted from the centrally located current electrode allowing the impedance matrix to be formed by the principle of linear superposition in terms of voltage and voltage difference measurements between adjacent electrodes. The impedance matrix is inverted and used to generate a set of tool responses, which when properly compared to a set of tool responses previously generated by computer simulation and addressable by sets of borehole parameters and calibration factors, allows the corresponding borehole conditions to be deduced from the measured data.

Abstract: A well logging instrument for measuring the resistivity of relatively thin formation beds. A well logging instrument includes an elongated body member, serving as a single guard electrode, and a point current emitting measure electrode recessed therein. The instrument is lowered into a borehole and urged into contact with the wall of the borehole. A measure current emanates from the measure electrode into the formation for determining the resistivity thereof.

Abstract: A wall engaging pad for well logging comprises a face portion of electrically conductive material within which are disposed three or more current electrodes. The survey current emitted from the current electrodes is differently focussed. A suitable current return is furnished. A plurality of individual measurements having respective graduated depths of investigation are obtained and suitably processed to yield resistivity measurements. The body of the sonde carrying the pad may be used to enhance the focussing of the survey current.

Abstract: An improved passive telluric current system for geophysical prospecting having a sensor responsive to the electric field component of the telluric current for producing a capacitive charge, a tuner for deconvoluting the sensed electric field telluric signal, and a cross-over circuit for generating a stereo audio output containing the telluric information into a low band audio signal and into a high band audio signal in order to enhance the frequency transitions contained in the telluric signal in the ears of the operator.

Abstract: The response characteristics of a combination of hole-centered electric logging tools in a variety of borehole conditions can be obtained by means of impedance values as entries of a matrix resulting from measurements over a series of depth increments, utilizing an array of M electrode assemblies of equal incremental spacing positioned on a rigid mandrel. While the array moves continuously along the borehole, currents are emitted independently and sequentially from first one and then the other of current electrodes located at the shallow and deep ends of the array, allowing the impedance matrix to be formed by the principle of linear superposition in terms of voltage and voltage difference measurements between adjacent electrodes.

Abstract: The response characteristics of a combination of hole-centered electric logging tools in a variety of borehole conditions can be obtained by means of impedance values as entries of a matrix resulting from measurements over a series of depth increments, utilizing an array of 2M-1 electrode assemblies of equal incremental spacing positioned on a rigid mandrel. While the array moves continuously along the borehole, current is continuously emitted from the centrally located current electrode allowing the impedance matrix to be formed by the principle of linear superposition in terms of voltage and voltage difference measurements between adjacent electrodes.

Abstract: The response characteristics of a combination of hole-centered electric logging tools in a variety of borehole conditions can be obtained by means of impedance values as entries of a matrix resulting from measurements over a series of depth increments, utilizing an array of M electrode assemblies of equal incremental spacing positioned on a rigid mandrel. While the array is substantially stationary within the borehole, currents from each electrode are emitted independently, one at a time, allowing the impedance matrix to be formed by the principle of linear superposition in terms of voltage and voltage difference measurements between adjacent electrodes.

Abstract: The response characteristics of a combination of hole-centered electric logging tools in a variety of borehole conditions can be obtained by means of impedance values as entries of a matrix resulting from measurements over a series of depth increments, utilizing an array of 2M-1 electrode assemblies of equal incremental spacing positioned on a rigid mandrel. While the array moves continuously along the borehole, current is continuously emitted from the centrally located current electrode allowing the impedance matrix to be formed by the principle of linear superposition in terms of voltage and voltage difference measurements between adjacent electrodes.

Abstract: A measuring tool for producing geophysical measurements within a borehole comprises a crawler belt, at least a portion of which constitutes a support for a transducer. The crawler belt is continuously displaced within the bore hole by means of a suspension cable and guide pulley in cooperating relation with spiked shoes and retaining plates for maintaining at least the transducer-supporting portion of the crawler belt in a stationary position with respect to the borehole wall during each measurement stage.

Abstract: A soil probe, comprising, in one form, a cylindrical member of insulating material having a pair of metal, electrically conductive, ring electrodes mounted a short distance above a conical portion at the lower end of the probe, these ring electrodes lie flush with the outer surface of the cylindrical member and are spaced apart from each other by the insulating material. An electrical-electronic measuring system is connected to the electrodes by conductors providing identical line impedance for each ring. The system has an initial electronic portion inside the cylindrical member and close to the electrodes and has a second portion distant from the cylindrical member. A plurality of different frequencies of radio-frequency current is applied to the electrodes, for accurate determination of capacitance at the different frequencies. Therefrom are determined the dielectric dispersion characteristics of the soil.

Abstract: An electromagnetic logging apparatus is disclosed which employs dielectric-filled button antennas, in conjunction with tuning elements, to obtain improved operation. The apparatus can be used to measure the dielectric constant of formations surrounding a borehole.

Abstract: An electrode insulated from and mounted to the outside of a drill collar in a drill string positioned in a borehole is used for measuring formation spontaneous potential. A current measuring device, such as an ammeter, is connected through a varible ammeter resistor and a switch between the electrode and the drill collar. The ammeter measures current flow from the formation along the walls of the borehole to the drill string to determine the spontaneous potential of the formation at various points along the borehole while it is being drilled. The switch in the ammeter circuit is interrupted at a pre-selected rate and the ammeter current signal is connected through a lock-in amplifier to cancel random noise in the signal and produce an accurate measurement of the very small currents flowing between the electrode and the drill collar. The currents are indicative of spontaneous potentials in the formation.

Abstract: An insulating segment for a drill string electrode structure is presented. The insulating segment of the drill string includes a drill string segment having a recess along an axial length thereof with a first sleeve of insulating material in the recess on the recessed surface of the drill string segment and a second sleeve of insulating material on the first sleeve of insulating material. The first end second sleeves of insulating material are of different hardnesses, with the second sleeve being harder than the first sleeve. A plurality of electrode are embedded in the second sleeve.

Abstract: A replaceable insulating sleeve is disposed around the lower end of a drill string used in drilling a well. The sleeve is restrained from rotating relative to the drill string, but can be released and quickly slipped off the drill string in the field to permit rapid replacement if damaged, or if alternate equipment is required. The sleeve carries sensing means for measuring a characteristic of formations penetrated by the well. Anchor means on the sensing means prevents it from rotating relative to the sleeve.

Abstract: The present invention relates to a wheel electrode suitable for use with a device for making an electrical survey of a structure contained in an electrolyte. The wheel electrode includes a chamber which contains electrolytic solution and a porous rim. The rim includes a dielectric rim structure having at least one recess in its axial surface, a plurality of apertures passing through the rim structure into the recess, and at least one porous member securable in the recess and having a predetermined rate of permeation. A metal electrode is positioned in the chamber in contact with the electrolytic solution. An elastic porous rim cover is securable about the rim for making contact with the electrolyte. The rim cover is adapted to carry an electrically conductive solution to the electrolyte during wheel rotation. Generating mechanisms are spaced about the wheel electrode at predetermined intervals for generating a series of electrical signals as the wheel electrode rotates.

Abstract: An insulating and electrode structure for a drill string is presented. The drill string includes a drill string segment having a recess along an axial length thereof. The recess has a band of elastomeric nonconductive material therein which receives electrodes comprised of rings of conductive elastomeric material.

Abstract: An array of electrodes is presented for accurate and improved measurement of borehole resistivity. The electrode array comprises five electrodes mounted on a relatively short insulated segment of a drill string. Current flows from the first electrode to the second electrode and is sensed by third and fourth electrodes. Any leakage current from the first electrode is collected by a fifth electrode and is kept isolated from the current flowing between the first and second electrodes thus insuring accurate determination of apparent formation resistivity. A current source, preferably a constant current source is used to determine the current in the circuit of the first and fifth electrodes.

Abstract: Bore hole instrument and methods of manufacturing and using the same. The instrument includes an elongated flexible probe which is inserted into a bore hole and can travel freely around bends of relatively short radius in the hole. The probe includes a plurality of sensors, explosive charges or the like which are spaced apart and embedded in a flexible body comprising a mass of cushioning material, with a flexible outer casing of fabric having a high tensile strength. The probe is driven into a bore hole in piston-like fashion, and the flexible body enables the probe to travel freely around bends of relatively short radius. Instrumentation for processing signals from the probe is located at the surface of the earth, and a flexible cable interconnects the instrumentation with the probe.

Abstract: A replaceable insulating sleeve is disposed around the lower end of a drill string used in drilling a well. The sleeve is restrained from rotating relative to the drill string, but can be released and quickly slipped off the drill string in the field to permit rapid replacement if damaged, or if alternate equipment is required. The sleeve carries sensing means for measuring a characteristic of formations penetrated by the well.

Abstract: A borehole investigating apparatus includes, an elongated support member, a first pair of wall-engaging pad members individually disposed on opposite sides of the support member along a given line and a second pair of wall-engaging pad members individually disposed on opposite sides of the support member along a given line at right angles to the given line for the first pair. The apparatus further includes first and second pad extending means for respectively moving the pad members of the first and second pairs away from the support member and against the borehole wall. The apparatus further includes primary driving means and a force dividing mechanism coupling this primary driving means to the first and second pad extending means for enabling unequal lateral extension of the pad members of the different pairs..Iaddend.

Abstract: A method of seismic prospecting using electromagnetic grounded antennas to detect electromagnetic waves that are produced from acoustic waves in the earth's formation. Seismic waves reflected by a formation in the earth are converted into electromagnetic waves in the vicinity of the antenna according to the streaming potential theory. The antenna has two electrodes which detect the horizontal component of the electromagnetic waves, thus providing additional seismic information that is not readily available using standard geophones. Antennas are also not subject to coupling problems and thus provide more accurate information than traditional geophones. For example, using multicomponent detection, all three components of the seismic pressure gradient can be detected.