WO2010048906A2 - Dispositif permettant la génération d'ondes sismiques rotatives, système de capteur d'ondes sismiques rotatives et ensemble de mesure sismique - Google Patents

Dispositif permettant la génération d'ondes sismiques rotatives, système de capteur d'ondes sismiques rotatives et ensemble de mesure sismique Download PDF

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WO2010048906A2
WO2010048906A2 PCT/CZ2009/000129 CZ2009000129W WO2010048906A2 WO 2010048906 A2 WO2010048906 A2 WO 2010048906A2 CZ 2009000129 W CZ2009000129 W CZ 2009000129W WO 2010048906 A2 WO2010048906 A2 WO 2010048906A2
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seismic
rotational
generator
sensor system
sensors
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PCT/CZ2009/000129
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English (en)
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WO2010048906A3 (fr
Inventor
Johana Brokesova
Jiri Malek
Jaroslav Strunc
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Matematicko-Fyzikalni Fakulta Univerzity Karlovy
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Priority claimed from CZ20080689A external-priority patent/CZ2008689A3/cs
Priority claimed from CZ20080688A external-priority patent/CZ2008688A3/cs
Application filed by Matematicko-Fyzikalni Fakulta Univerzity Karlovy filed Critical Matematicko-Fyzikalni Fakulta Univerzity Karlovy
Publication of WO2010048906A2 publication Critical patent/WO2010048906A2/fr
Publication of WO2010048906A3 publication Critical patent/WO2010048906A3/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/02—Generating seismic energy
    • G01V1/143—Generating seismic energy using mechanical driving means, e.g. motor driven shaft

Definitions

  • the invention concerns the field of seismic measurements.
  • the invention in particular, concerns a device for generating rotational seismic waves (hereinafter referred to only as “the generator"), a measuring set containing the generator and a detection device based on the principle of the rotational seismic sensor system. It also concerns the method of seismic measurement, which makes use of the generator 10 and the rotational seismic sensor system. Seismic measurements using the generator and the seismic rotational sensor system according to the invention enable seismic prospecting using rotational ground motion, which helps in making more accurate determinations of the rock structure at depth.
  • Rotational seismic motions have so far been generated by ordinary seismic sources, natural earthquakes or man-made sources, e.g., explosive shots, various vibrators or drop testers. These sources, however, transform only a mostly small part of the energy into rotational components of seismic waves, the remainder of the seismic energy is transmitted in the ordinary (translational) components of seismic waves. Jhe
  • Gyroscopes and tiltmeters used, e.g., in aviation, or commercially accessible tri- axial rotational sensors, operating on the electro-chemical principle (Nigbor, R. L.
  • Seismic arrays e.g., Huang, B. S. (2003), Ground rotational motions of the 1991 Chi-Chi, Taiwan earthquake as inferred from dense array observations, Geophys. Res. Lett., Vol. 30, 1307-1310) which record rotational motion by approximating spatial derivatives of translational seismic motion measured by the separate seismographs of the array.
  • Laser gyroscopes based on measuring the interference of counter-directed laser rays (see, e.g., Schreiber, K. U. et al., Ring Laser Gyroscopes as Rotational Sensors for Seismic Wave Studies, In: Earthquake Source Asymmetry, Structural Media and Rotation Effects, Teisseyre, R., Takeo, M., Majewski, E. (Eds.), Springer, 2006). These gyroscopes provide very accurate measurements. Their disadvantage is that they are very expensive and bound to a single location, because they are very large and must be mounted in specially modified conditions (special structures, underground spaces, etc.). These gyroscopes measure rotational motion around one axis only.
  • Fig. 1 Prospection measurement with the generator is schematically shown in Fig. 1 in which the rotational seismic waves, excited by the generator and reflected from the individual boundaries in the rock structure are measured, e.g., by a set of three sensor systems.
  • rotational seismic waves in this description represents rotational motions, which are related to the propagation of seismic waves in the ground, and which need not necessarily be of a wave nature.
  • rotational waves and rotational motions may be used interchangeably in the sense given above.
  • the first subject-matter of the invention is the device for generating rotational seismic waves, hereinafter referred to as the generator of rotational seismic waves or briefly as the generator, containing a fixed part for anchoring in the ground, a revolving part and a braking mechanism for immediate braking of the rotational part, in which rotational seismic motions are generated by immediately stopping the revolving part, whereby energy is transmitted into the rock massive.
  • the generator (schematically illustrated in Fig. 2) contains the following fundamental parts: - the fixed part, which anchors the generator to the ground and serves as an axis for the revolving part;
  • Weights which represent most of the weight of the generator, may be placed at the end remote from the axis of rotation, and - the braking mechanism, which enables the revolving part to be stopped instantaneously.
  • a preferred embodiment of the generator according to the invention is equipped with a braking mechanism which operates by the rotational arms impacting braking rods, or by the cogs of the cog wheel of the revolving part engaging the cogs of the cog segment of the fixed part.
  • a braking mechanism which operates by the rotational arms impacting braking rods, or by the cogs of the cog wheel of the revolving part engaging the cogs of the cog segment of the fixed part.
  • the generator optionally also comprises a motor (not shown in Fig. 2) which drives the revolving part, and a control unit.
  • Another subject-matter of the invention is a seismic measuring set comprising the generator of rotational seismic waves described above and at least one suitable rotational seismic sensor, preferably the rotational seismic sensor system described below.
  • Another subject-matter of the invention is the rotational seismic sensor system, which comprises one or more pairs of identical seismic sensors, each pair being fixed to the non-deformable frame of the system, and the sensors being located so that they measure seismic oscillations along two parallels, these parallels being at a distance from one another which is much smaller than the wavelength of the P-waves in the ambient rock, and the line connecting the sensors of a given pair must be perpendicular to the axis of rotational motion, which is to be measured, and must not be parallel with the axis, along which the translational motions are measured. It may also contain a control unit.
  • the rotational seismic sensor system measures the generated rotational motion and the rotational motions related to the reflected and/or refracted waves, which have passed through the rock.
  • the subject-matter of the invention is also a seismic measuring set, which comprises the rotational seismic sensor system according to the invention and a suitable generator of seismic waves.
  • the measuring set according to the invention preferably comprises a generator of rotational seismic motions and a rotational seismic sensor system, as described above.
  • the measuring system may also comprise a control unit, which measures the generator's revolutions, issues the command to start and stop the motor and activate the braking mechanism, or to return the whole device to its initial condition prior to repeated measurement, and records the time variation of the signal from the sensor of rotational motion.
  • the control unit may be used to control the generator, but also to control the whole process of the seismic measurement.
  • the signals from repeated measurements may also be combined in the control unit in order to achieve high sensitivity, and the complete mathematical processing of the measurements until the resultant seismogram, which is then available in analogue and digital form, may be carried out in the unit as well.
  • the control unit of the set according to the invention preferably comprises implemented computer program, which controls the method of measurement and data processing, which increases the sensitivity of measuring rotational seismic motions significantly.
  • Another subject-matter of the invention is the method of generating rotational seismic ground motions, which consists in using the generator, anchored with its fixed part in the ground, and the mobile part of the generator, after being activated, is stopped instantaneously by the braking mechanism; this instantaneous stopping transmits energy into the rock massif.
  • Still another subject-matter of the invention is the method of seismic prospecting, which consists in generating rotational seismic motions in the manner described above according to the invention and measuring the response by a sensor, preferably by the sensor system according to the invention and, finally, processing the measurements and evaluating them by the control unit.
  • the whole measurement and data processing is carried out with the aid of a computer program, which is implemented, for example, in the control unit, and which makes measurements I) of the time variation of the exciting seismic signals, and II) of the time variation of the reflected seismic signals, and the step mentioned above of processing the measurements is made with the aid of the computer program, which includes the following steps: 1 ) computing the correlation function using formula V1 (for details see below) and 2) addition is carried out over separate experiments (index i in formula V2) and 3) addition is carried out over pairs of sensors (index j in formula V2) and if the addition is non-iinear, steps 2) and 3) are carried out in the order given.
  • a commercially available portable computer i.e. notebook can be used as the control unit.
  • the control unit can also communicate, wireless or via conductors, with a distant computer, in which the said program or part thereof has been implemented.
  • the control unit may also contain a device for storing the measured data (e.g., RAM, a hard-disc type device, data DVD, etc.) which are then processed.
  • the method of seismic prospecting in which the seismic measuring set according to the invention is used to generate rotational motions and to measure them, is also a subject-matter of the invention.
  • the generator works in the following manner:
  • the motor gradually rotates the revolving part.
  • the latter may have different forms, e.g., a rotating disc or ring, or the form of several revolving arms distributed at regular angular intervals around the axis of rotation.
  • the motor After reaching the required speed, i.e. number of revolutions per unit time, the motor is switched off to avoid disturbing the subsequent measurement, and the revolving part then continues revolving by inertia.
  • the control unit then activates the braking mechanism, which immediately stops the revolving part.
  • the kinetic energy is thus transferred to the fixed part, anchored in the ground. This energy transforms to the energy of rotational seismic waves, which propagate downwards into the rock massif.
  • the source pulse is recorded by the rotational seismic sensor system, which is located under the generator.
  • the rotational seismic waves propagate through the rock structure and are reflected from the inhomogeneities in the rocks and/or they become refracted so that part of the energy of these waves reaches the Earth's surface again, where they are recorded by one or more rotational seismic sensor systems measuring the rotational components of seismic motion.
  • the processing of the measured data yields the times of propagation of the reflected and/or refracted waves and their amplitudes. Together with other data, these data are necessary for determining the rock structure at depth.
  • the generator of rotational waves may be used either in connection with one of the rotational seismic sensors, known to the skilled person from the state of the art (however, these measurements will be less accurate) or in combination with a newly developed rotational seismic sensor system, which is described below. In combination with the latter, a special method of measurement and processing of the results, which increases the sensitivity of the measurement considerably, is used.
  • the generator described has a substantially higher efficiency in generating rotational ground motion than all state-of-the-art man-made sources used to date. This enables new methods of seismic prospection, based on the rotational components of seismic motion, to be developed. These components should be processed together with traditionally measured translational components.
  • the description of seismic motion cannot be complete without that of the rotational components, because, according to generally accepted physical conceptions, the motion of a general mass point has 6 degrees of freedom and can be uniquely described only if three translation and three rotational components are considered.
  • the pulse of the rotational seismic waves be generated at a relatively high frequency (tens of Hz) which then has a resolution for the inhomogeneities of the rock massif. This is achieved by stopping the revolving part instantaneously without reverse impact.
  • the solution pursuant to the invention enables the generator to be used for sequentially repeated experiments, essentially the same pulse of rotational seismic waves being generated thereby.
  • Another advantage of the generator described is its relatively small dimensions and weight, which makes it easy to move the whole device.
  • the rotational seismic sensor system used together with the generator, is also easy to move and install in any region of interest thanks to its size and small weight. Another of its advantages is the simultaneous measurement of rotational and translational components of seismic motion, which is necessary if a complete description of the ground motion at a given point is to be provided.
  • the processing method used enables better identification of weaker reflected and/or refracted rotational seismic waves than other methods being used and known to experts. This decreases the energy which the generator has to generate in one pulse. The smaller weight and size of the generator thus suffice. This also contributes to the mobility of the whole measuring system.
  • Fig. 1 Schematic illustration of prospection measurement using the invention.
  • G indicates the generator, sensor systems S1 , S2 and S3 form the set of three sensor systems, and the arrows are a simplified illustration of the seismic waves reflected from the separate boundaries in the rock structure.
  • Fig. 2 Side-view (A) and ground-plan (B) of the generator with revolving arms under motion.
  • Fig. 3 Side-view (A) and ground-plan (B) of the generator with revolving arms after braking.
  • Fig. 4 One of the possible embodiments of the rotational seismic sensor: 1 1 - projection of the centres of all pairs of sensors, imaginary polygons and fixed designs of circular shape, 12 - vertical sensor, 13 - horizontal sensor, 14 - rigid circular frame, 15 - imaginary polygons with even number of apexes.
  • FIG. 5 Block diagram of the functioning of the control unit.
  • SN - other sensors 101 - command to set generator to initial condition, 102 - command to switch on motor, 103 - measuring speed of arm rotation, 104 - command to switch off motor, 105 - command to activate braking system, 106 - command to decrease sensitivity of central sensor, 107 - measurement of input signal, 108 - command to increase sensitivity of central sensor, 109 -measurement of reflected signal, 1 10 - measurement of reflected signals, 1 1 1 - transfer of collected data for processing, 1 12 - output signals.
  • Fig. 6 Diagram of processing measurements by the processor; G - generator, S1 , S2, ..., SN sensor systems according to invention, C1 to C3 - three components of rotational motion.
  • Fig. 7 Photograph of one embodiment of the sensor system.
  • S - sensor system U - control unit (convertor part), G - part of the generator (fixed part, which forms the axis of rotation, anchored in the ground).
  • Fig. 8 Signals measured by geopho ⁇ es a, b, c, d (top panel) and rotational seismograms A, B (bottom panel) from the test measurements described in Example 3.
  • the generator according to the invention (see diagram in Fig. 2) comprises the following basic parts: Fixed part P, revolving part O, and braking mechanism B_.
  • the fixed part P of the generator comprises at least two, preferably three, firm arms 1_, which are anchored in the ground and fixed to the central column 2.
  • the ends of the arms 1 are embedded perpendicularly in holes in the ground, which are pre-drilled by an auger.
  • the central column 2 is located in the axis of rotation of the revolving arms 3 of the revolving part O of the generator, which are fixed to the column 2 by two bearings 4 with little friction under rotation.
  • the braking mechanism B is fixed to the central column 2 between the bearings.
  • the revolving part O of the generator comprises e.g. a fixed disc or ring, rotating in a plane perpendicular to the central column 2 of the fixed part, which is also the axis of rotation.
  • the disc or ring is fixed to the central column 2 by bearings 4 which enable rotational motion with minimum friction.
  • the revolving part O has preferably (Fig. 2) the form of two or more revolving arms 3 spaced at regular angular intervals around the axis of rotation, i.e. of the central column 2.
  • Each arm is formed, e.g., of two rods 3.1 , which are obliquely fixed to the central column 2 using bearings 4.
  • weight 3 ⁇ 2 At the circumference of the revolving disc, or at the end of the rod, is fixed weight 3 ⁇ 2, which may have many forms.
  • a preferred embodiment is the use of a hollow cylindrical tank as the weight 32, which is, e.g., filled with water or sand. This makes transportation easier, and the weight need be filled only at the measurement site.
  • the cylindrical shape of the weight is advantageous due to small air resistance under rotation.
  • the braking mechanism B of the generator serves for instantaneous stopping of the revolving part O.
  • An advantageous alternative of breaking the revolving part, especially if it is formed by a rotating disc, may be the engagement of the cogs of the cog wheel, fixed to the revolving part O with the spaces between the cogs of the cog segment fixed to the fixed part P. Both cog elements lie in the plane perpendicular to the axis of rotation.
  • the system is activated, e.g., by releasing a latch so that the mobile part moves vertically downwards due to its own weight and pushes the cog wheel to contact the cog segment.
  • Preferred alternative of the braking mechanism B is the impact of braking rods 5 on the revolving arms 3, specifically on their rods 3.1.
  • Figure 2 shows the generator with revolving arms 3 prior to braking, Fig. 3 after braking.
  • the braking mechanism B in this case, comprises two or more braking rods 5.
  • a preferred embodiment comprises the same number of braking rods 5 as the number of revolving arms 3.
  • Braking rods 5 are positioned so that they will not hinder the motion of the arms 3 and are secured by means of split pin 6, which is controlled, e.g., electromagnetically by means of relay 7 and tie bar 8.
  • the split pin Upon command from the control unit, the split pin is released and the braking rod 5 crosses the path of the lower part of the arm 3. After being released, the braking rods 5 fall downwards due to their own weight, and their motion is accelerated by springs 9.
  • the lower part of the braking rods 5 meshes with the groove in disc 10, which is fixed to central column 2. After braking, it is necessary to prevent reverse impact. This can be done in several ways, e.g., by a rubber suction adapter or electro- magnet (the specialist is sure to find other equivalents easily). It is convenient to use a mechanical latch. At the point of impact on braking rod 5 there is an orifice into which the latch, connected with revolving arm 3, falls upon impact.
  • the latch mechanism may, e.g., be designed as a latch, which is equipped on both sides by triangular segments, held apart by a spring. Upon passing through the orifice, the segments are compressed, after passing through they expand and prevent the reverse impact. It is convenient if the latch is also operated electromagnetically. This allows the control unit, after terminating the experiment, to return the device to its initial condition without manual intervention of the operator. This is convenient because high sensitivity is achieved by multiply repeated measurements.
  • the generator motor (not shown in Fig. 2) rotates the revolving part O, to which the rotational moment is transferred, e.g., with the aid of a V-belt. It is preferred to use a motor, which is able to rotate the generator clockwise or counter-clockwise. It is also preferred to equip the motor with a battery, which serves to start the motor, to feed the control unit and the electromagnetic control of the braking mechanism.
  • the generator constitutes a convenient seismic measuring system, which is able to generate and exceptionally sensitively record rotational seismic motions.
  • the rotational seismic sensor system (Fig. 4) of completely new design comprises one or more pairs of identical seismic sensors (the term "identical” is meant in the sense of the characteristics of the output signal) e.g., currently available geophones (i.e. seismic sensors, which are based on electromagnetic sensing of the motion of an inertial mass suspended on a specially shaped spring).
  • the pair of sensors is in each case fixed to the solid frame of the sensor and is located so that it measures seismic oscillations along two parallel straight lines (this is briefly designated in the description as “parallel sensors”). These parallel straight lines are at a distance much closer than the wavelength of longitudinal seismic waves (P-waves) in the ambient rock. Usually a distance of a few decimetres is involved.
  • the line joining the sensors of a given pair must be perpendicular to the axis of rotational motion to be measured and must not be parallel with the axis, along which translationai motion is measured.
  • the number of sensor pairs depends on the number of components of rotational motion (number of axes of rotation about which the measurement is taking place simultaneously) and also on the maximization of the sensitivity-to-cost ratio. A sensor system with a larger number of sensor pairs is more sensitive, but also more expensive.
  • the individual sensors measure one translationai component of seismic oscillations.
  • the rotational seismic sensor system (as shown in Fig. 4) comprises pairs of vertical sensor YZ and horizontal sensors 13.
  • the sensors 12, 13 of the vertical and horizontal pairs of sensors are located in parallel planes.
  • the vertical as well as horizontal sensors 12, 13 are located at the apexes of a regular polygon 15 with an even number of apexes (in the special case of two sensors, this polygon reduces to a line section).
  • the vertical and horizontal sensors 12, 13 are fixed to the rigid frame J4, e.g. a metal structure, the essential property of which is that it is non-deformable.
  • the principle of measuring the rotational components with a pair of identical parallel sensors lies in computing the difference between the signals from the two sensors (differential motion). If the signals do not contain the rotational component, the signals from the two sensors would be identical, because they are fixed to the solid frame, which cannot be deformed.
  • the differential motion from a pair of sensors with parallel axes therefore, corresponds to the rotational motion in the plane defined by these axes.
  • the sensitivity of the measurement of a given pair is directly proportional to the sensitivity of the individual sensors and to the distance between their axes. The distance between the sensors of a given pair, however, cannot be increased too much, because the condition that the frame is non-deformable and that its dimensions are essentially negligible with respect to the wavelength of P-waves, must be satisfied.
  • the preferred embodiment of the above sensor system is the rotational seismic sensor system for measuring the rotational motion around a vertical or horizontal axis (axes).
  • the terms “vertical " and “horizontal” are related to the position (orientation) of the instrument with respect to the gravitational field in the course of the measurement with the sensor system fixed to the ground. If the system is not fixed to the ground, these terms are used only to differentiate between two mutually perpendicular directions, along which the axes of the sensors, making up the sensor system, are oriented.
  • For measuring the rotation around a single axis at least one pair of sensors with axes in the plane perpendicular to this axis is required.
  • the rotational seismic sensor system thus comprises at least one pair of sensors, preferably at least three pairs of sensors, more preferably more than three sensor pairs in the specific configuration described above.
  • FIG. 7 Another preferred embodiment of the sensor system is shown in Fig. 7.
  • the set comprising the generator and sensor of rotational seismic motion preferably comprises a control unit, which automatically controls the generator and sensor system and more preferably also processes and evaluates the observed data.
  • the control unit is substantially a computer, which records the data from the sensors, switches the motor on and off, activates the braking mechanism and returns the generator to its original condition.
  • To the control unit are connected the motor, electromagnetic relay, seismic rotational system and revolution counter, e.g., optical revolution counter.
  • the principle of the optical revolution counter is in that an optical ray is interrupted by the passage of rotating arms.
  • the braking mechanism is activated, e.g., when the rotating arms are in a suitable position with respect to the braking rods.
  • the control unit also takes care of processing the measured data in the manner described below.
  • the control unit comprises implemented computer program, which processes the data and is described by the flow chart in Fig. 5, and one specific embodiment is described in Example 3.
  • the computer program mentioned may also be implemented in a distant computer, which is used to process the data.
  • FIG. 5 shows the embodiment wherein all activities being carried out by a single control unit U, which controls generator G (this embodiment comprises revolving arms and braking rods) and sensor systems SOS.
  • Control unit U consists of operation unit IJl and processor U2. This unit issues command 101 to generator to assume initial condition (initialization GJ.). The unit then issues command 102 to motor G2 to switch on.
  • Optical bar G3 issues signals 103 on the speed of rotation and the present position of the arms, these data being evaluated in the control unit on a current basis. After the arms achieve sufficient speed, the unit issues command 104 to switch the motor off.
  • the unit When the arms are in optimum position, the unit issues command 105 to activate braking system G4 and also command 106 to decrease the sensitivity of sensor system Sl, located just below generator G. This sensor system records the exciting rotational signal and sends appropriate signal 107 to the control unit. Immediately afterwards, the unit issues command 108 to increase the sensitivity of sensor system SI.. Sensor system SJ . , and possibly other systems S2 to SN then record rotational signals 109, 1 10, which are reflected from the rock massif (e.g., by inhomogeneities). Thereafter all accumulated data are transferred VA. to processor U2, where they are processed currently or later. It is convenient to repeat the whole process of initialization, switching on and stopping the generator many times in order to increase the sensitivity of the measurement. The result of the measurements and processing in processor LJ2 are output rotational seismograms 112, corresponding to the individual sensor systems SJ . to SN.
  • the processor carries out the processing according to the scheme in Fig. 6, wherein G is the generator, SJ., S2, ..., SN are the rotational seismic sensor systems, and CJ. to C3 the three components of rotational motion.
  • G is the generator
  • SJ., S2, ..., SN are the rotational seismic sensor systems
  • CJ. to C3 the three components of rotational motion.
  • the figure corresponds to the situation, in which more than one sensor system is used and each of them measures rotational motion around three mutually perpendicular axes (parallel for all sensor systems).
  • the person skilled in the art will understand possible modification of controlling the generator and measuring device, e.g., with a different braking mechanism.
  • the following time records are available for processing the seismic measurement: a) exciting signals b lk (t) (first few tenths of a second of the record), b) reflected and/or refracted signals x lk (t) (the rest of the record), where / is the number of the experiment and k the number of the seismic sensor.
  • the processing is carried out in several steps:
  • the exciting signal is non-zero only within a short time interval, and it is sufficient to integrate just within these limits. If the reflection arriving at time f has the same orientation as the exciting signal, function K v (t) is positive, otherwise negative. If no reflection arrives, K,,(t) is zero (assuming an ideal case with no noise). The reflections may thus be identified by finding the local maxima of function
  • Non-linear combination of signals can be applied in this formula, e.g., using the GAS method (Malek, J., Kolinsky P., Strunc J., Valenta J. 2007: Generalized average of signals (GAS) - a new method for detection of very weak waves in seismograms. Acta Geodyn. et Geomat, 4, No. 3, 5-10).
  • GAS Generalized average of signals
  • the generator essentially corresponds to the scheme in Fig. 2. It has two revolving arms, located opposite to one another with respect to the axis of rotation. Tanks of cylindrical shape, volume 16 litres, are fixed to the arms. Prior to activation, holes are drilled with an auger for anchoring the generator, and the underground part is buried. The tanks are filled with water, and each of the weights thus has a weights about 21 kg. Their horizontal positioning is checked with a level. The measurement is then activated by means of the control unit. This unit then controls the whole procedure. It switches on the motor and thereby the arms begin to revolve. Once the required speed is achieved, it switches of the motor. After a pause of a few seconds, it activates the braking mechanism.
  • the braking rods are dropped at a suitable moment so that they become engaged in the grooves before they are impacted by the revolving arms.
  • the revolving arms become attached to the braking rods, the revolving arms are stopped, and rotational seismic waves are generated.
  • the output from the rotational seismic sensor system begins to be recorded.
  • First small amplification is applied, to record the strong exciting pulse truly, and the sensitivity is then increased (e.g. a hundredfold) for recording the reflected waves.
  • the latches are released and the revolving arms are turned back by several tens of degrees.
  • the braking rods are pulled up and secured by split pins.
  • the generator is then prepared for further use.
  • Example 2 To distinguish very weak reflections, the whole procedure is repeated many times, and the results are added up (see Example 3). In half of the cases the generator is rotated clockwise, in the other half counter-clockwise. Example 2
  • This particular embodiment of rotational seismic sensor system consisted of four horizontal geophones of the LF-24 type (by Sensor Nederland B. V.) with a flat frequency response for frequencies in excess of 1 Hz. Geophones, fixed to non-deformable (steel) frame of cylindrical shape, diameter 40 cm (Fig. 7) were used as sensors. The sensor system was located on the surface, close to the fixed part of the Generator of rotational ground motion. A notebook computer with a UDAQ 1408 (Tedia) converter card was used as the control unit.
  • the fixed part of the generator was sunk into the ground.
  • the particular embodiment of the generator had four revolving arms.
  • the braking mechanism was made of iron tubes, which were originally kept in a horizontal position and, at a suitable moment, blocked the revolving of the arms (they dropped into groves dug in the ground). Thereby the revolving arms impacted the braking rods, the revolving arms stopped practically instantaneously and rotational seismic motions were generated.
  • These were recorded by the sensor system, consisting of four horizontal LF-24 type geophones (by Sensor Nederalnd B. V.) with a flat frequency response for frequencies in excess of 1 Hz.
  • the geophones were fixed to a cylindrical frame, diameter 40 cm (Fig. 7).
  • the sensor system was located on the surface, close to the fixed part of the generator.
  • a notebook computer with a UDAQ 1408 (Tedia) converter card was used as the control unit.
  • Fig. 8 The top panel shows the outputs from 4 geophones (a, b, c, d). The differences between these records are due to the rotational components, which are shown in the bottom panel for 2 pairs of geophones (a, c) and (b, d).
  • This analogue signal is digitized by means of an A/D converter (by Tedia, s.r.o.) with a range set to ⁇ 5 V. It follows that the maximum range of the recorded oscillation velocity is approximately ⁇ 3.33 mm/s.
  • the converter has dynamics of 22 bites, which means that its overall range is divided into approximately ⁇ 10 6 levels. The smallest oscillation speed, which can be distinguished (LSB) is therefore 3.33 nm/s.
  • the diameter of the disc frame, to which the geophones are fixed is 20 cm. It follows that the LSD expressed in radians amounts to 16.65 nrad/s. This can be considered the basic sensitivity of this particular sensor system. This sensitivity is constant in the frequency range of 1 to 200 Hz.

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Abstract

D’une manière générale, la présente invention concerne la prospection sismique. En particulier, l’invention concerne un générateur d’ondes sismiques rotatives, un dispositif de mesure basé sur le principe d’un système de capteur d’ondes sismiques rotatives et le procédé de mesure sismique, mettant en œuvre le générateur et le système de capteur d’ondes sismiques rotatives. Des mesures sismiques au moyen du générateur et du système de capteur d’ondes sismiques rotatives permettent une prospection sismique utilisant le mouvement du sol, qui aide à déterminer la structure rocheuse en profondeur avec une plus grande précision. L’invention concerne de manière spécifique le générateur d’ondes sismiques rotatives, qui comporte une partie fixe permettant son ancrage dans le sol, une partie tournante, un mécanisme de freinage pour l’arrêt instantané de la partie tournante, et éventuellement un moteur et/ou une unité de commande. L’invention concerne également le système capteur d’ondes sismiques rotatives, comportant une ou des paires de capteurs sismiques identiques parallèles, chaque paire de capteurs étant fixée à un châssis non déformable. L’invention concerne en outre l’ensemble de mesure sismique, comportant le générateur et au moins un capteur de mouvement sismique rotatif, de préférence le système de capteur d’ondes sismiques rotatives selon la présente invention. L’invention concerne enfin le procédé de collecte de données sismiques, mettant en œuvre l’ensemble selon l’invention, de préférence le système capteur d’ondes sismiques selon la présente invention. L’invention concerne également le procédé de prospection sismique, mettant en œuvre l’ensemble selon l’invention, de préférence avec un programme d’ordinateur pour contrôler l’activité de l’ensemble, la collecte de données et le traitement de données.
PCT/CZ2009/000129 2008-10-30 2009-10-29 Dispositif permettant la génération d'ondes sismiques rotatives, système de capteur d'ondes sismiques rotatives et ensemble de mesure sismique WO2010048906A2 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
CZ20080689A CZ2008689A3 (cs) 2008-10-30 2008-10-30 Generátor rotacních seismických vln, seismická mericí souprava obsahující tento generátor a zpusob seismického pruzkumu
CZ20080688A CZ2008688A3 (cs) 2008-10-30 2008-10-30 Rotacní seismický senzorový systém, seismická mericí souprava obsahující tento systém a zpusob seismického pruzkumu
CZ2008-688 2008-10-30
CZ2008-689 2008-10-30

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9594174B2 (en) 2013-02-01 2017-03-14 Westerngeco L.L.C. Computing rotation data using a gradient of translational data
US10048395B2 (en) 2013-02-01 2018-08-14 Westerngeco L.L.C. Computing a gradient based on differences of plural pairs of particle motion sensors
US10928528B2 (en) 2013-02-01 2021-02-23 Westerngeco L.L.C. Computing rotation data using a gradient of translational data
US10408954B2 (en) 2014-01-17 2019-09-10 Westerngeco L.L.C. Seismic sensor coupling
WO2017114517A1 (fr) * 2015-12-31 2017-07-06 Univerzita Karlova V Praze Système de capteurs opto-mécaniques de mesure de mouvements sismiques et procédé de mesure sismique à l'aide du système
US10859720B2 (en) 2015-12-31 2020-12-08 Univerzita Karlova & Ústav Struktury A Mechaniky Hornin Av Cr, Vvi Opto-mechanical sensor system for measuring seismic movements and a method of seismic measurements using the system
CN109683195A (zh) * 2019-01-09 2019-04-26 武汉理工大学 一种地震动摇摆分量获取方法
CN109683195B (zh) * 2019-01-09 2020-04-24 武汉理工大学 一种地震动摇摆分量获取方法
WO2022117131A1 (fr) * 2020-12-01 2022-06-09 Ústav struktury a mechaniky hornin AV CR, v.v.i. Générateur d'ondes sismiques harmoniques et procédé de prospection sismique

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