Abstract: An apparatus for generating signals and energy for transmission to a large mass. The apparatus incorporates a pulsed generator such as a compensated pulsed alternator for storing and for discharging large amounts of energy in a controlled manner for transmission through a vibrator or similar electromechanical device. In the field of seismic exploration, the apparatus discharges seismic source energy into a land mass or water to generate seismic waves which are reflected from the interface between subsurface geologic formations. The pulsed generator permits the seismic source energy to be discharged in a controlled manner to shape the energy signal, and permits large quantities of energy to be discharged to increase the penetration depth and strength of the reflected signals.

Abstract: An apparatus and method for generating a seismic signal in the earth consisting of positioning a force-modulating means on the surface of the earth and then positioning a vehicle such that at least some of the weight of the vehicle is supported by the force-modulating means. At least one of the vehicle drive wheels is then rotated to cause the force applied to the earth by the force-modulating means to change thereby generating a seismic signal in the earth.

Abstract: A multivibrator waveform monitoring system uses a plurality of seismic energy sources for giving vibrations to strata and a prospector, connected to a geophone, for measuring reflected vibrations. Each of the plurality of seismic energy sources includes a vibrator, a communication unit and a control unit for controlling the starting of the vibrator based on phase difference cancellation information and an operation starting instruction from the prospector. The prospector includes a communication unit and a synchronization control unit for controlling the synchronization of each of the seismic energy sources.

Abstract: A vibrator for producing seismic vibrations in the earth is carried by a vehicle. The vibrator has a base plate, a reaction mass and support plates and a lifting and lowering apparatus for raising and lowering the vibrator between a raised transportation position and a lowered operating position in which the base plate is pressed against the ground. The lifting and lowering apparatus includes piston and cylinder units each connected at one end to the vehicle chassis and at the other to a support plate. In one embodiment, the piston and cylinder units are attached to the vehicle by belt-type pivotable bearings to permit swiveling of the vibrator so that the base plate is tiltable to adapt to an uneven earth surface. In another embodiment, the piston and cylinder units are attached to the vibrator by spherical pendulum support bearings which also allow swiveling and tilting of the base plate.

Abstract: A simple and low maintenance Ride Control System (RCS) for Air Cushion Vehicles (ACV) is presented. This RCS reduces the effect of water wave generated pressure pulses on ACV ride by venting the pressure pulses from the pressurized supporting gas cushion and/or restricting gas flow into a powered blower that supplies the pressurized supporting gas cushion as the pressure pulses occur. The preferred embodiment utilizes high aspect ratio low moment of inertia vanes that are individually driven by brushless electric servo motors and the vanes can rotate in either direction through 360 degrees. A vane braking and locking mechanism is presented that brakes and locks the vanes in a closed position in the event of power failure to the vane drive motors. A further feature of the invention is a venturi that is positioned between the powered blower and the pressurized supporting gas cushion to reduce the effect of the pressure pulses on blower operation.

Abstract: A broad band seismic vibrator includes a hydraulically-operated actuator with a piston shaft depending from the actuator. A spherical member or ball is secured to an end of the shaft and received in a socket provided in an anvil. The spherical member or ball is securely clamped to the end and in its clamped condition affords the sole support for the actuator. Hydraulic means is provided for unclamping the spherical member to enable the positioning of the actuator in selected degrees of inclination from vertical and azimuth.

Abstract: The SH wave generating apparatus includes a driving plate (1) of increased rigidity; a fixing device (6) provided on the bottom of the driving plate for fixing the driving plate onto the earth's surface; a plurality of hydraulic actuators (2) mounted on the driving plate, which have reaction masses and act tangentially on the same circumference from the center of the driving plate; and a driving device (4,5) for reciprocating the plurality of hydraulic actuators (2) at a controlled frequency, thereby generating transverse waves. The plurality of hydraulic actuators (2) are equidistantly mounted on the driving plate (1), and each include a cylinder (2) and a piston rod extending therethrough. The said piston rod is mounted at both ends on supports (3) fixed to the driving plate (1) and the cylinder acts as a reaction mass. Alternatively, the piston rod extending through the cylinder 2 may be provided at both ends with reaction masses.

Abstract: A simple, low cost, and reliable, normally cyclic, fluid control valve that in preferred configuration includes one or more rotary valve elements where such valve elements have openings that align with each other and/or with a flow passageway thus forming an aperture for fluid flow during valve cycles. Rotary valve elements may be oriented in different directions to connecting ducts and may have a variety of shapes with a preferred shape being cylindrical. Simple motors drive rotary valve elements such that a rate of valve cycling and/or amount of aperture can be easily controlled by a controller such as a microprocessor. Easy valve servicing and installation are other features. Dynamic sealing of the fluids is preferably accomplished by use of simple low cost labyrinth seals.

Abstract: A method and an apparatus for mass retrieval for an acoustic pulse generator are disclosed herein. In an impulse type seismic generating apparatus an air spring, mechanical spring, controlled pressurization of an air spring or other energy storage medium is employed to use potential energy to raise the impact mass to a resting position above an earth contacting baseplate as quickly as possible after the impact mass strikes the baseplate.

Abstract: A method and apparatus for providing shear waves in a marine environment in which a shear wave source penetrates the surface sediment of a water bottom. The shear wave generating source includes an actuator/reaction mass system mounted inside a structural ring of a housing section. A cross-shaped structure at the top of the apparatus serves as a passive reaction mass and as a moment arm support for reversibly motor driven propellers enclosed in shrouds at the outer ends of the structure. A thruster system provides dynamic positioning. The cross-shaped structure and housing section are connected by a structurally stiff member, such as a vertical tube. Pistons provide actuation against a reaction mass located within the housing structure, and motion of the housing structure generates shear waves which propagate in the subsurface formations.

Abstract: The method and apparatus for providing elliptical polarized shear waves in a marine environment in which a shear wave source penetrates the surface sediment of a water bottom includes dual actuator/reaction mass system mounted inside a structural ring of a conical housing section. A cross shaped structure at the top of the apparatus serves as a passive reaction mass and as a moment arm support for reversibly motor driven propellers enclosed in shrouds at the outer ends of the cross shaped structure. A thruster system provides dynamic positioning. The cross shaped structure and housing section are connected by a structurally stiff member, such as a vertical tube. Pistons provide actuation of two reaction masses located within the housing structure, and the motions of the reaction masses generate shear waves which propagate in the subsurface formations.

Abstract: Method and apparatus for generating seismic energy in offshore areas includes energy propagating means for directing energy downwardly vertically into an earth formation. A carrier contains an elongated rigid coupler means that extends from the carrier at the water level to the seat floor. A base plate may be connected to the lower end of the coupler means. The coupler means may be a section of pipe. Driving means on the carrier drives the coupler means to cause sound energy to emanate from the coupler means or base plate into the sea floor. Such means may be a hammer-type device or a vibrator-type device. Alternatively, the lower end of the coupler means or the base plate may be driven by means of a vibrator-type device to cause sound waves to emanate from the coupler means or the base plate directly into the sea floor.

Abstract: Seismic signal generating apparatus of the impact type that includes a signal generator having an impact mass therein, a base plate or coupling member that is engaged by the impact mass to generate the signal, a housing attached to the generator that encircles the impact mass and extends toward the base plate, and means for excluding water from within the housing so that the impact mass travels only through gas prior to engaging the anvil. The apparatus also includes control means for positioning the generator angularly and azimuthally.

Abstract: An apparatus and method for maximizing the shear wave energy imparted into the soil upon the impacting of a base plate by an impact mass from a seismic generator. A seismic generator is disposed at an angle relative to a line generally perpendicular to the surface to the ground. The angle varies with soil conditions and the angle is determined by locating an accelerometer on the base plate of the generator and observing the horizontal acceleration rate as indicated by the accelerometer. If the acceleration rate exceeds a predetermined value, the anguular disposition of the generator s changed to decrease the angle either manually or automatically until the acceleration rate no longer exceeds a predetermined value.

Abstract: Apparatus for generating a controlled parameter elliptically polarized shear wave into an earth medium. The apparatus consists of a baseplate for engagement with the earth medium in omni-directionally resistant manner and a reaction mass and actuator assembly affixed thereto and energizable to impart reciprocal lateral forces to the baseplate that exert a predetermined resultant force at a controlled rate of rotation.

Abstract: A wheeled, self-propelled tractor has a percussion tool or hammer mounted on its forward end and an impact transmitting means carried on the tractor below the hammer. In accordance with one aspect of the invention, the impact transmitting means comprises a metal frame having a strong rigid top plate that is struck by the hammer and a downwardly opening cavity in which wood timbers are mounted to transmit the impact from the plate to a cemetery marker. Repeated blows to the market applied through the impact transmitting means will drive the marker into the ground until it is flush with the ground surface where it will not interfere with mowing. The frame is fastened on the vehicle by a suspension system that includes tension springs which keep the wood timbers in a horizontal plane but permit the frame to move downwardly each time it is struck by the hammer.

Abstract: The present invention relates to a method for generation of elliptically polarized shear waves in an earth medium using two shear wave vibrators engaged to the earth medium in cross-polarized attitude and driven at sweep rates having variable phase displacement.

Abstract: Apparatus including transportation structure for generating elliptically polarized shear waves in soft earth medium. A suitable carrier includes a jack assembly for transporting shear wave apparatus that includes a telescoping tube for earth engagement. The shear wave apparatus, including a major or lower reaction mass and a passive top reaction mass, is raised and lowered by the jack assembly into operative position while the energy-coupling telescoping tube is extendably forced into an earth medium so that, during shear wave generation, the vibration source or reaction mass is continually imparting shear wave energy into the progressively extending telescoping tube to effect continual energy coupling into the surrounding earth medium. The reaction mass is driven by a plural hydraulic actuator system that imparts elliptically polarized vibration to the telescopic tube which, in turn, imparts elliptically polarized shear waves into the surrounding earth medium.

Abstract: A device for generating elliptically polarized shear waves for introduction into a soft earth medium including marshy and water-covered earth surfaces. The device consists of a shear wave generator coupled to a coupling tube having a conical lower end that is maintained in energy-coupling relationship within the earth medium. Shear waves such as elliptically generated shear waves are introduced into the tube member for travel along the tube and further earth coupling about the bottom cone member as it is progressively driven into the earth medium. Suitable hold-down weight is utilized to maintain most effective coupling pressure on the cone member, and, support equipment, either land or marine vehicle, may include crane and alignment structure for continually maintaining the tubular vibrator member in proper vertical attitude during operation.

Abstract: The disclosure relates to a seismic vibrator having an airbag isolator, a transducer for monitoring the instantaneous air pressure within the airbags, a summer to add the pressures within each air bag and a calibrated weighting network to convert the composite pressure for display as holdown weight on a meter and for comparing the measured holdown against a preset threshold that is used to enable or disable sweep generation or operation of an inducer. The system also includes structure for comparing the measured holdown against a preset threshold that is used as a feedback signal to the lift system and for providing a signal proportional to holdown weight to the sweep generator for use as a feedback signal to modify the amplitude of the force generated by the actuator.

Abstract: Apparatus for generating a controlled parameter elliptically polarized shear wave into an earth medium. The apparatus consists of a baseplate for engagement with the earth medium in omni-directionally resistant manner and a reaction mass and actuator assembly affixed thereto and energizable to impart reciprocal lateral forces to the base-plate that exert a predetermined resultant force at a controlled rate of rotation.

Abstract: A device for generating in the ground longitudinal and transverse acoustic waves by a mass striking a target element coupled with the surface of the ground. The target element is recessed in a central part thereof and have an inner wall slanted with respect to the vertical in the form of, for example, a truncated cone. The mass is fixed to the end of an arm pivoting with respect to a support structure in the form of a parallelepipedic cage, which is movable by a cylinder between a high transport position and a low position in which the target element is coupled with the ground a drive causes raising of the mass by pivoting the arm with the geometry of the assembly being calculated so that the mass strikes the inner slanting faces perpendicularly thereto, and thus creates both P and S waves.

Abstract: The improved seismic vibration apparatus includes variable length control means located so as to effectively and efficiently position the vibrator relative to the base plate and apparatus to isolate the vibrator from the control system and from the vehicle frame so that effective seismic vibration is imparted into the base plate and consequently into the earth.

Abstract: Disclosed is an apparatus for imparting only shear wave energy into the earth comprising a vibrating pad for connection to a mobile support, such as a wheeled vehicle, and means for vibrating the pad to impart at least two polarizations of shear wave energy into the earth. One such means includes azimuthally rotating the pad and/or the vibration energy generator.

Abstract: An impact type surface seismic source powered by compressed air includes an elongated piston which moves within the bore of a cylindrical firing tube suitably mounted above an earth contacting target. The firing tube consists of two or more tubular sections slidably joined in telescopic relation. When the piston is allowed to fall from a cocked position, compressed air enters the bore above the piston through side ports and drives the piston downwardly. At the same time, the inner sliding section or sections of the firing tube are exposed to the same air pressure within the bore and are also driven downwardly. In this way, the bore of the firing tube lengthens automatically to provide a longer stroke for the piston and thus a greater attained kinetic energy of impact for a given operating pressure as the piston reaches the target. The apparatus is designed for mounting on a transport vehicle so that the firing tube itself may be raised in operation and lowered for reduced vehicle profile during transport.

Abstract: An impulsive seismic generator is mounted on a swamp buggy suitable for operations both in a marshy environment and on land. The generator employs a target plate which may be lowered into a body of water or mud beneath the buggy so as to contact subsurfaces of varying degrees of firmness. The submerged components of the generator are surrounded by a water-tight barrier which isolates the space between a descending mass and the receiving target plate from the surrounding fluid.

Abstract: Two tracks are mounted between a vibratory source of shear, or horizontally travelling, wave siesmic energy and its transport vehicle. The tracks are parallel to each other in the direction of horizontal movement of the source when vibrating. One track is attached to the source, and the other to the vehicle. Pressurized rounded resilient members, which may be either spherical bags or wide tires, are mounted between the tracks to isolate the vehicle from vibrations, insuring that the seismic energy enters the earth.

Abstract: A rigid, earth-contacting target for use with an acoustic signal generator is designed to be impacted by a mass propelled downwardly by compressed air or other energy source. The target includes an upper impact-receiving member slidably interfitted with a lower ground-contacting member. An elastomeric disc is confined between the upper and lower members so as to experience three-dimensional compression in response to such impact. The bulk modulus of the elastomer determines the degree to which the rate of acceleration of the lower member is reduced as compared to that of the upper member, and thus in turn, controls the frequency content of the resultant acoustic pulse.

Abstract: This invention is an improved type of shear wave vibrator are carried by a support vehicle and utilizing telescoping tubes for energy engagement within an underlying earth medium. A shear wave vibrator so constructed is particularly desirable for use over marshy or soft surface earth areas. The device consists of a jack assembly supporting a shear wave vibrator relative to a suitable carrier vehicle in vibrationally isolated manner. The vibrator structure consists of a pair of parallel, elongatable telescoping blades for earth penetration and engagement with a passive reaction mass pivotally secured across the top portion of the telescoping blades and an active mass/vibrator system pivotally secured across the lower portion of the telescoping blades adjacent the earth surface.

Abstract: An underwater vibrator is specifically adapted for generating a shear wave in a seabed and includes a frame; locomotion apparatus attached to the frame for moving the vibrator over the seabed; and cable means connected between a surface support vessel and the vibrator. The vibrator also includes buoyancy and apparatus for selectively controlling the buoyancy along with apparatus for selectively engaging the seabed with the vibrator. Apparatus is also carried by the vibrator for viewing the location of the vibrator under the water which includes lights and television equipment.

Abstract: The weight of a transport vehicle and the actuator of an impact type seismic source carried thereby is partially transferred by means of hydraulic lift cylinders to a freely movable earth contacting baseplate positioned beneath the actuator. In operation a mass is propelled by the actuator along a prescribed slant path to strike the baseplate. Shear strain is induced in elastomeric pads sandwiched between the hydraulic lift cylinders and the baseplate if the baseplate shifts sideways under such a slanting blow. The pads then exert a force to restore the vehicle and the actuator to a correct perpendicular alignment over the baseplate. Upper and lower position locator means fixed respectively to the hydraulic lift cylinders and to the baseplate interface with the elastomeric pads and fit slidably within each other so as to transmit vertical force from vehicle to baseplate.

Abstract: A bi-planar pontoon paravane is towed by a marine vessel and controls the depth and position of a towed seismic source array. The bi-planar pontoon paravane is made up of a buoyant bridge with right and left wings attached to the long sides of the bridge, the wings projecting into the water and, in concert, providing a side force. The paravane is towed by a tow line connected to an adjustable bridle which in turn is connected to the paravane. Remote adjustment of the bridle is provided by an hydraulic valve on the vessel controlling an hydraulic motor and gear arrangement on the paravane to adjust the bridle. Adjustment of the bridle adjusts the angle of attack of the paravane. The paravane provides a housing formed below the bridge and between the two wings for housing the seismic source array. A boom on the vessel is attached to the seismic source array, through the bridge, when the assembly is to be placed in or removed from the water.

Abstract: A vibratory seismic surface source includes a single vibrating mass, the energy of which is coupled to the earth through a ground contacting base plate. Means are provided for varying the inclination and azimuth of the vector path traversed by the reciprocating mass, such that any desired combination of compressional and shear waves, both SH and SV type, may be generated and recorded simultaneously at a point on the earth's surface remote from the source.

Abstract: A wheeled, self-propelled tractor has a percussion tool or hammer mounted on its forward end and an impact transmitting means carried on the tractor below the hammer. In accordance with one aspect of the invention, the impact transmitting means comprises a metal frame having a strong rigid top plate that is struck by the hammer and a downwardly opening cavity in which wood timbers are mounted to transmit the impact from the plate to a cemetery marker. Repeated blows to the marker applied through the impact transmitting means will drive the marker into the ground until it is flush with the ground surface where it will not interfere with mowing. The frame is fastened on the vehicle by a suspension system that includes tension springs which keep the wood timbers in a horizontal plane but permit the frame to move downwardly each time it is struck by the hammer.

Abstract: A seismic source is disclosed which is particularly useful for generating horizontally polarized shear waves in the earth for seismic surveying. It comprises an elongated, hollow, substantially vertical cylinder having an earth-contacting pad pivotally mounted to its lower end by a horizontal pivot shaft extending parallel with the front-to-back centerline of a transport vehicle. The lower surface of this large rigid pad contains multiple, blade-like teeth extending parallel with the pivot shaft for gripping the earth's surface for transmitting powerful horizontally polarized shear stress impulses into the earth. The cylinder contains a slidable piston-like reaction mass. The bottom of the cylinder is a strong upwardly diverging conical surface serving to focus and direct upwardly the discharge blast from each port of an air gun extending horizontally and with the axis of the air gun being oriented parallel with the pivot axis and being located a short distance above the pivot shaft.

Abstract: An apparatus for introducing vibrations into the ground including a container having electrodes mounted therein with electrical connections leading from a source of electric potential to said electrodes, salt water substantially filling the container, and means for placing the container on the ground in position to transmit vibrations to the ground.

Abstract: A vehicle for seismic surveying fitted with a shock source device, and an electronic control and display device. The control and display device has a display panel which provides a display of required shock positions, and a movable display which moves along the display of impact positions in dependance upon vehicle travel to facilitate positioning of the vehicle at the required shock positions.

Abstract: The present invention is an improvement to conventional baseplates for imparting seismic energy to an earth formation. A baseplate typically has a plurality of downwardly disposed triangular prism-shaped cleats for engagement with the earth surface above an earth formation under seismological investigation. At least one leaf spring is supported about midway along its length from the lower surface of the baseplate and between the cleats. An elongate horizontal ejector member is slidably interconnected to the respective ends of the spring. In operation, as the baseplate is lowered into engagement with the earth surface the ejector member is moved upward and the leaf spring is compressed. When the baseplate is lifted upward the restoring force of the leaf spring results in a generally downward force against the ejector member.

Abstract: A transportable seismic energy source having a baseplate for contacting the earth, an upper master cylinder affixed at its lower end to the base plate and extending uprightly from it, a receiving cylinder of outside diameter less than the internal diameter of the master cylinder and supported coaxially within the upper portion of the master cylinder, the master cylinder and receiving cylinder being filled with liquid, a slug firing gun mounted to the master cylinder and arranged so that the gun muzzle extends coaxially and above the receiving cylinder.

Abstract: Multiple vehicle-transported impact-type surface seismic sources designed to shoot along slant paths to create combined compressional and shear wave pulses in the earth are provided with radio controlled actuators. The azimuth of each shooting path is automatically referenced to magnetic north so that signals of equivalent wave form contents are produced despite vehicle misalignments and without reliance upon individual vehicle operators.

Abstract: A transportable hydraulic seismic transducer has a seismic energy source connected to a pad for imparting elastic waves to the underlying ground. The energy source has a reaction mass with a single diameter cylinder formed therein, a double ended piston reciprocally mounted in the cylinder with a piston rod extending from opposite ends of the piston and a pair of bushings fitted within the cylinder at opposite ends to provide bearing surfaces for the opposite ends of the piston rod. A piston may be ringed and a liner fitted into place within the cylinder with the rings forming a seal with the liner. The piston may also be ringless and a liner made of a bushing material fitted within the cylinder so that between the piston and the liner, an adequate seal is provided. The use of the single diameter cylinder or bore permits the total machining of inserted parts such as the bushings and liners to be done before inserting in the reaction mass bore.

Abstract: A vibrator baseplate for use in a seismic signal transducer system has a bottom plate with a dome centrally located thereon. A pair of partial domes overlap the central dome on opposite sides thereof. Top plates are attached to the partial domes, which are also attached to the bottom plate. Internal rib stiffeners are provided within each dome and gusset members extend between the partial domes and the top plates. Means are provided to connect the baseplate to the seismic signal transducer system. Alternatively, the baseplate comprises a bottom plate with an elongate eccentric dome attached thereto.

Abstract: Apparatus for measuring the force actually exerted by the base plate of a seismic vibrator on the earth surface is provided. This apparatus consists of a plurality of individual sensor elements, which are arranged on the side of the base plate which is directed towards the earth surface. The sensor elements couple the energy from the base plate to the earth surface.

Abstract: A vibratory seismic surface source includes a single vibrating mass, the energy of which is coupled with the earth through a ground contacting base plate. The vibrating mass is connected to the base plate by means of a ball and socket joint which constitutes a universal pivot for the vibratory axis of the mass. Thus, this vibratory axis may be made to assume any vector path with respect to a seismic line. In this manner, any desired combination of compressional and shear waves, both SH and V type, may be generated and recorded simultaneously at a point on the earth's surface remote from the source.

Abstract: A full waveform seismic source is described which is adapted to propel a heavy mass powerfully downward against the surface of an earth-contacting target plate. Means are provided for rotating the barrel of the actuator about two mutually perpendicular horizontal axes so that energy can be delivered to the earth along a plurality of preselected slant paths. In this way, any desired combination of compressional and shear waves, both SH and SV type, may be generated at a point on the earth's surface. The target is contoured so that any slant path followed by the accelerating mass always impacts the target normal to its surface.

Abstract: A vibratory seismic surface source includes a single vibrating mass, supported above and independently of an earth-contacting base plate. Means are provided for varying the inclination and azimuth of the vibrator axis. After the vibrator is oriented in any desired direction, it is then lowered along its vibratory axis so that it bears directly against the hemispherically concave upper surface of the base plate. When the vibrator is actuated in this position of contact, any desired combination of compressional and shear waves, both SH and SV type, may be generated and recorded simultaneously at a point on the earth's surface remote from the source.

Abstract: A vibratory seismic surface source includes a hydraulic vibrator the energy of which is coupled into the earth through a ground contacting base plate. The vibrator is supported above and independently of the base plate so that it may be pivoted about a first rotational axis within a truck-mounted gimbal-type frame which itself is tiltable about a second horizontal rotational axis perpendicular to the first. After the vibratory axis is oriented in the desired direction the vibrator is lowered so as to contact a suitably contoured upper surface of the base plate. Inclination of the vibrator is accomplished by "push-pull" operation of pairs of oppositely-directed hydraulic cylinders.

Abstract: A vibrator seismic source has a hydraulic system, including a pad, for applying reciprocating forces to the ground and sensor means for generating a feedback signal representative of the force applied to the ground. Circuitry is provided for generating a pilot signal representative of the desired force to be applied to the ground. The pilot and feedback signals are single sideband shifted to increase both frequencies by a predetermined frequency. The high frequency pilot and feedback signals have their phase difference conventionally detected and provided to a digital computer for phase shifting the signal for controlling the vibrator so that the feedback signal is in phase with the pilot signal. In another embodiment, the instantaneous phase of each signal is computed continuously by a digital computer. The control signal digital representation is corrected to correspond with the pilot digital representation and an analog output signal is generated to provide the proper analog control signal.

Abstract: A dual-mode vibrator for alternately injecting P-waves and S-waves in the earth including a hydraulically driven shaker assembly, a ground-contacting base plate, and a jacking means for raising and lowering the base plate relative to a vehicle. The shaker assembly is supported above, and coupled to the base plate by a supporting means. The supporting means has a first configuration for coupling the shaker assembly to the base plate for generating P-waves and a second configuration for pivotally coupling the shaker assembly to the base plate and to a rigid member associated with the vehicle for injecting S-waves.

Abstract: Apparatus for incremental cylinder length control in hydraulic seismic vibrators having increased frequency range. The vibrator apparatus (10) of the type having a reaction mass (38) and axial cylinder bore (42) utilizes hydraulically movable end sleeves (86 and 96) in each end of the cylinder bore (42) so that the end sleeves (86 and 96) can be controllably positioned thereby to alter the cylinder volume and adjust the hydraulic drive system (18) for maximum efficiency relative to operating frequency.