DE2036514C3 - Method and device for underwater seismic prospecting - Google Patents

Description

is decreased; furthermore, additional towing force is required and the arrangement is relatively complex and expensive.

A method for improving the interpretability of seismograms is known (DT-AS 12 05 295), at 5 which a filter stage of different filters is used to remove organized and random disturbances remove. This is achieved in this known proposal in that the two or more successive blasting signals by means of different filters with different Bandwidths and different phase delays are filtered and the signals of each track correspond to one of the same geophone group at the amplifier output. It is thus known in the case of the Proposal basically made a time lapse, so that those gained from several explosions Records of an explosion appear to have originated.

Furthermore, from DT-OS 14 73 951 a method for determining the time of receipt of Known signals that have passed through a medium, wherein a medium is supplied with a number of waves and these wave trains are caught after they have passed through the medium. Here everyone knows Wave train has a certain frequency and limited length that differs from that of other wave trains, and it a combined signal is formed by placing the intercepted wave trains in the time relationship are combined, in which the captured wave trains, which the wave trains without passing through the Medium correspond to are in phase during a period of a wave train. From this publication is known in seismics to work with combined signals and a temporal summary of the Signals to achieve.

Furthermore, a run-time method has become known in seismic under the designation "VIBROSEIS" method ("Erdöl und Kohlen", 1964, pp. 699-707), from which it emerges that in the explosive seismic before In 1964 (without convincing success) attempts were made as the repeatable core of the "message" to use a Ricker wavelat for correlation, since undesired interferences have similar pulse shapes and then be correlated. In this aforementioned method, although the technology of Cross-correlation, which is known per se in the factory, is used but is not a Process in which explosives are used which are detonated at greater depths in the water have been.

Finally, a method for defining an external reflector geometry is known ("Geophysics" April 1959, pp. 233-261), with the characteristic Properties of the complex input signal by evaluating the automatic correlation of the received Signal can be determined. In order to be able to define the inverse operator, it is then important that the original complex signal that is to be inverted, a phase minimum is different from that inverse operator cannot be determined. However, such a method is in connection with the Bubble pulse not usable because the bubble pulse sequence is not a phase minimum but a mixed phase. Their inverse value can only be obtained from a direct knowledge of one's own actual characteristic properties to be determined. This citation is known to those of ordinary skill in the art as too infer that when an explosion is made in Wassei, the initial pulse will repeat having. If one knows the characteristic de; Body of water, the characteristic properties can the repetitions, especially the time intervals and their corresponding amplitudes! will. If you have this information, an inverse filter can be created. The citation relates thus only on the seismic filter theory in connection with the proposal according to the invention is assumed to be known per se. In connection with this citation it is also important that that any suggestion of the use of explosives in offshore exploration was avoided will.

From the above it follows that in known seismic underwater exploration systems with Detonators working at greater depths are the only attempts to solve this The problem has been the following, i. H. the secondary gas bubble expansions physical to solve with a cage, the disadvantage being accepted that the performance of the Arrangement has been significantly reduced due to the loss of energy

The object of the present invention is to generate sufficiently large seismic energy Water depth in addition to and subsequent to the primary pressure surge occurring secondary pressure surges, the by oscillations of the gas bubble in the water, for example caused by an explosive generated, recorded and taken into account, and not - as is the case with already known methods, e.g. after the Tlexotir process is common - to suppress.

The invention is based on the knowledge that there are significant advantages when you use it fails to suppress the physical phenomenon of secondary bubble expansion, and that the Corrections required to eliminate incorrect results are carried out at a later stage d. H. in displaying and evaluating the signals generated by the seismic pulses generated by the Earth layers are reflected under the sea floor. In the case of the invention, the Shifting the correction from the marine environment to the receiving, indicating and evaluating Arrangement of the surveying device itself laid. It was recognized that there was no cage for this is required so that the exploitation of a maximum of seismic energy generated by the detonation marine seismic survey arrangements is generated

According to the invention it is proposed in a method of the type specified that the second Signals are recorded representing the non-reflected wave train passing through the primary and the secondary) expansions) that a Operator is created, which the curve form of the second Signals are converted into a preselected curve shape and the first signals are filtered with the operator so that that output signals arise which correspond to output signals, which in the absence of secondary Expansions of the bladder would have been produced.

Another embodiment of the method according to the invention is set out in spoke 5

To carry out the method according to the invention, a device is proposed that thereby

is characterized in that at least one additional pressure transducer is provided for generating second signals, which represent the non-reflected wave train, which is created by the primary and the secondary (s) expansion (s), and that a device for influencing an operator, the curve shape of the second signals in a preselected waveform transforms, filters out the first signals, wherein the operator generates output signals corresponding to output signals that would have been generated in the absence of secondary, ₀ expansion of the bladder.

Further features of the invention emerge from the subclaims.

In the case of the present invention, explosive charges are thus detonated at such a depth brought that the bubble pulse train can be formed without hindrance, and that either the Influences of secondary bubble expansion at the stage of processing the recorded seismic Data are removed or the characteristic pulse train produced by the secondary bubble expansions is used to assess the quality of the resulting seismic data with the help of a increase temporal compression of the occurrence in coincidence with the first expansion.

When practicing the method according to the invention, an explosion, a bubble generated, which contains an expanding gas volume of high pressure, made at a sufficient depth, this prevents gas from escaping directly into the atmosphere. The first expansion of the The gas bubble creates an acoustic impulse in the water, which then hits the layers of the earth beneath the Sea floor is reflected. The gas bubble collapses following the first expansion and expands again so that at least a first secondary acoustic bubble pulse is generated in the water which is also reflected by the layers of the earth beneath the sea floor. The reflections of the The first acoustic pulse and at least the first secondary acoustic bubble pulse are displayed and from this a seismic wave train is derived. Then an operator becomes an characteristic feature of the first secondary acoustic bubble impulse created, and the seismic one Wave train is acted upon by the operator. Preferred operators and how to create them are described below in connection with the drawing.

In the following the invention in connection with the drawing on the basis of an exemplary embodiment explained it shows

F i g. 1 a schematic representation of a device, with which a bubble is created underwater, which is an initially expanding volume of a Contains high pressure gas,

F i g. 2 the primary and secondary expansions and contractions of the gas bubble,

F i g. 3 is a waveform representing a bubble pulse train represents which is produced by the primary and the secondary bubble expansions,

F i g. 4 the seismic wave sequence recorded,

F i g. 5 the desired seismic sequence,

Fig.6 schematically shows a processing system below Using a cross correlator and

Fig.7 shows a processing system below Use of a convolver.

In Fig. 1 shows an ignition system for generating underwater explosions, each explosion a bubble containing an expanding volume of high pressure gas at such a great depth creates that the gas does not come into direct contact with the atmosphere. Preferably has a charge starting device explosive charges 12 which can be ignited by impact. Each charge 12 contains one Delay detonator, which detonates the charge at a distance from the starting device 10, there during operation, the launch device 10 of a seismic ship 14 at a certain depth is dragged under the surface of the water. The directional stability of the starting device 10 is through suitable mine deflectors 15 are maintained. A flexible line 16 couples a charging device 18 Deck of the ship 14 with the launching device 10. The charges 12 migrate under the propulsion of the Water pressure through line 16.

For example, the launcher 10 is behind the seismic ship 14 at a speed from six to ten knots per hour at a depth of about 6-15 m below the surface of the water drawn. An operator, in turn, takes precautions to keep each cargo 12 under the water pressure moved into the starting device 10. When the load 12 has reached the end of its path, its Movement is stopped by a striking element 20 which acts on a detonator in the charge 12, whereby an ignition device in charge 12 is actuated. Then the charge 12 emerges from the starting device 10 by the flow of water under pressure between the cargo and the wall 22 of the starting device 10 pushed out. The detonation of the ejected charge 12 is made so long by the delay detonator delayed until there is a distance of about 2 - 3 m between the loaded load and the itself moving starting device 10 is reached.

According to FIG. 2, in the event of a detonation, the chemical energy in the charge 12 suddenly turns into kinetic energy converted into a rapidly expanding gas bubble. A bubble 30 is thus built up in the water, which is a contains expanding gas volume of high pressure. Since the gas bubble 30 at a depth of about 10 to 15 m is generated, it cannot come into direct contact with the atmosphere. The gas bubble 30 experiences a very rapid primary expansion indicated by the radially outwardly directed arrows on the bladder 30 according to FIG. 2 and which causes the surrounding water to be suddenly strongly compressed. The compression of the water produces the desired primary pulse 30 'of FIG. 3, who passed through the water continues to the outside and is then reflected by the layers of earth beneath the sea floor, displayed and from a guide cable 24 (streamer cable) by detectors, e.g. B. Hydrophones recorded will

Following the primary expansion, the gas bubble falls into one shown at 32 in a known manner State together, as indicated by the arrows oriented inward in the radial direction The compressed bladder 32 then expands again to the expanded position 34. The expansion of the bladder 34 generates a first further acoustic bubble pulse 34 '(FIG. 3) in the water, which afterwards through the water The first further pulse 34 'is also emitted from the layers of the earth below the sea floor reflected Subsequently, the bubble 34 collapses into a contracted gas bubble, which then becomes a

709 609/135

third expansion, d. H. a second further expansion, etc.

The entire sequence of gas bubble expansions and contractions forms a pulse sequence of acoustic ones Impulses.

One method of displaying this pulse train is that a corresponding display device 40, e.g. B. a pressure transducer or hydrophone, in addition to those of the cable 24, is provided as close as practically possible to an explosive charge 12. The arrangement of the detector 40 relative to the starting device 10 is determined by how far the detector 40 can withstand the high overpressures generated in the water by the explosions following the detonations of the charges 12, ₅ and also by how far the Detector 40 can reliably reproduce the pressure waveform generated by the explosion of charge 12. The detector 40 is therefore arranged far enough away from the detonation site that it is not damaged or influenced by the detonation.

The detector 40 transmits the duration of the occurrence of each of the successive ones acoustic bubble impulses, and also, if possible, the amplitudes and the impulse shapes of the initial impulse and the first and subsequent further pulses to a recording device on board the Ship 14. A record is made of the train of pulses emitted by detector 40 are recorded, preferably by the conventional seismic recorder, and simultaneously with the recording of the indicated seismic signals caused by the signals that be reflected from the layers of the earth beneath the sea floor. The reflected seismic signals are indicated by conventional seismic cable 24 which gives a seismic waveform 24 ', as in Fig. 4 shown.

Figure 3 depicts a typical recording of a bubble pulse train 40 'as indicated by detector 40 40, typically a hydrophone. As stated above, the primary expansion of the bubble 30 produces a relatively large initial momentum 30 '. The second expansion of the bubble 34 generates a first, further bubble pulse 34 ', the third 45 bubble expansion generates the second, further bubble pulse 37, the fourth bubble expansion generates the third further bubble pulse 38, etc. Simultaneously with the recording of the bubble pulse sequence 40' with the aid of the detector 10 is advised in the seismic Aufzeichnungsge- 50 on board of the vessel 14, the seismic wave train 24 '(Figure 4) with the aid of the cable 74 of FIG. 1 is recorded ande erseits can ßlasenimpulsfolge 40' are derived from the conventional seismic data, such as they are recorded by means of cable 24 in the conventional manner by recording the direct arrival of seismic signals at each detector array in cable 24. This can be accomplished by adjusting the timing of the recordings obtained from the plurality 60 of seismic detector arrays in cable 24 so that all incoming signals are recorded as if they were being recorded simultaneously. In other words, this means that this technique consists in eliminating the extraction received on direct arrival from the individual lines, one line being provided for each detector group ADe these

Lines are then summed up. Random noise is canceled out in such a sum as the primary pulse and subsequent secondary bubble pulses amplify, so that the cumulative trace is a fairly faithful representation of the pulses making up pulse train 40 '(Fig. 4). In any case, with each detonation of a 12, a bubble pulse sequence 40 'is recorded, a table of Hearing 7 »; i;» i.— "; - ■ ---

ersS,
created.

ervÄ

K ^PUIS , ^{relative to the primary lm} P "ls shown in Figure 3, for example

f: ZsTi Tr ™ ^de _f ^{m first sec =} Bsi

ZeftinIri, " ^ndde u ^{m initial} impulse 30 'equals t _u das .mo! 37 ^ nHΤ ⁰ * ¹ '" ^{the 2 wide} secondary bladder impulse 37 and the first secondary bladder impulse 34 '

Ll "^? ^{Can also be a} table for the

Frfin,? ^{1 a] significantly} en feature of the present saeti r ° ^{ator of a} charakiristi-34 "first" H? * ^ * "^'Sekunda ™ bubble pulse this (L u ^is? _F ^smische wave 24' with Si? Z" ^beaufschl W ^as with a desired

is obtained n "· the ImDulsfoll S 4 anßezei g lw ould when the ζ BI only Jf η Γ, a ein2i & s in P uls would, - By J m h ISC i.e. as kaft!" 24 "(Figure 5)!

,. only from the initial pulse 30 '
Bubbles in ^r _you ^e . ^r f ^en ^? ^{According to FIG} . 6, the operaZS ^{g W} J is used ^{to build up a} correlation on which the seif r ^e ™ ^ends · ^which acts in a cross correlator 62 l ", ndT.h '" ^WelIenzu « ²⁴ '.

^ mathematical or mechanical devices

l l ^{FroM elegt are} · ^{that si i} QKL

f ^{in exactly the} """Chen way t ^A S ^ix" ignal variable ^{ziehun "to-housed T>> Vlbroseis} process" is set. ^eS Q ^uerk ° Telators 62 generates the ismic wave train 24 "

"°?" ^Co ^ ' ^a tion _p erator 60 for ^{the primary} pulse 30' and ^ ^{individual values} for each of the e 'H ^{secondary blue} pulses exist.

S Sf * ^ve v ^{rsetzt and have their ei} ^ ^ne

£ ^bha ? »8ness of the above-" ^S ° ^lcher ° p ^{erator is} ^ special-

7Κ? Γ ^known

separate _Ζε 1

^{W or the} goperator can

^WeUenfol g ^{e 2} 4 'abandoned R ** * ^{ht riföh}

the Impute ™ XT! i ^aaü . ^< ? ^{le Ze} MntervaIle between pansionen _ ^, _6C! change the amplitudes.

Leren embodiment according to FIG. 7 can be the operator. 70 j »« λ—: - "-" _: _ yj »

. ., and their corresponding

m the way shown in Fig.3

This Wiener operator is the displayed seismic wave sequence 24 'in a convolver 72 given up. In this context, reference is made to the mathematical investigations by Norbert Wiener This is referred to for the first time in book form with the title “Extrapolation, Interpolation and Smoothing of Stationary Time Series (New York, John Wiley and Sons, 1949). A whole A number of books and articles have been published to complete this technique. In the construction an inverse filter, as is known in communications engineering, an operator 70 is created, which a given, converts the observed waveform to a desired output waveform 74. The operator 70 is as that inverse Fourier transform of the quotient of the complex spectra of the observed and desired Curve shape built up. For example, in the seismic method described here, the observed The waveform may be a bubble pulse train 40 ', and the desired waveform may be a pulse, a Ricker wave or a minimal phase wave with a conventional amplitude spectrum more limited Bandwidth. The steps to be performed are in the processing and analysis of stationary time series The seismic wave sequence 24 ′ recorded by the device 72 is correspondingly known processed so that the desired wave sequence 24 "is created

In a further embodiment of the invention, due to the data processing, it is that for seismic Operations is available, possible, the bubble pulse train 40 'according to FIG. 4 in time to the start pulse

30 'to compress, thus the effect of an amplified single pulse source and thus the desired seismic Wave sequence 24 "arises.

According to the present invention, one technique for carrying out this exemplary method is as follows: The sequence of secondary bubble expansions is removed from the original seismic sequence 24 ', depending on one of the exemplary embodiments described above, so that the processed sequence 24 "is formed; then the processed sequence 24" is formed. subtracted from the original sequence 24 'in order to obtain a bubble contour line A which now contains only the reflected signals from the secondary bubble pulse sequence. It is assumed that the first bubble is equivalent to an initial pulse, and on this assumption, the bubble outline A is processed in accordance with one of the embodiments described above so that all subsequent bubble pulses are removed and a processed trace B is obtained which only contains the reflected signals from the contains first secondary bubble pulse; the processed trace B is then shifted in time by the time period fi, whereby the signals corresponding to the reflections from the first secondary bubble pulse are aligned with those from the initial pulse on the processed trace 24 ", and the time-displaced trace B is added to the processed trace 24" to get the reflected signals from the primary pulse. This process can then be repeated for each subsequent bubble pulse in order to amplify the reflected signals from the initial pulse.

1 sheet of drawings

Claims (10)

Patent claims: 1. Process for underwater seismic prospecting, in which an underwater explosion takes the form a rapidly expanding volume of gas is generated under high pressure to convert a gas bubble into to such a depth that the gas bubble following the primary explosive expansion collapses and re-expands at least once, the primary explosive expansion and the secondary (s) expansion (s) each generate an acoustic impulse from earth layers is reflected below the sea floor, and taking a wave train of first signals that represent acoustic impulses which are reflected from the layers of the earth below the sea floor are generated and displayed, characterized in that a) second signals (40 ') are recorded which represent the non-reflected wave train which caused by the primary and secondary expansion (s) (30 ', 34', 37, 38) will, b) an operator is created which converts the curve shape of the second signals (40 ') into a preheated Waveform reshaped, and c) the first signals (24 ') are filtered with the operator so that output signals (24 ") arise, which correspond to output signals, which in the absence of secondary expansions the bubble would have been generated. 2. The method according to claim 1, characterized in that the operator is created so that he the curve shape of the second signals (40 ') is compressed in time. 3. The method according to claim 2, characterized in that the operator is created so that the Time interval or the time intervals between the primary expansion and a secondary expansion or secondary expansions. 4. The method according to claim 3, characterized in that the operator is created so that the ratios (ar, aw a ^ lay, ...) of the amplitudes (a ₂ ; 93 ...) of secondary expansions relative to the amplitude ( ai) the primary expansion can be used in addition to the time interval between the primary expansion and a secondary expansion. 5. A method of underwater seismic prospecting in which an underwater explosion occurs in the form of a rapidly expanding volume of gas is generated under high pressure to convert a gas bubble into to such a depth that the gas bubble following the primary explosive expansion collapses and re-expands at least once, the primary explosive expansion and the secondary (s) expansions) each generate an acoustic impulse from the layers of the earth is reflected below the sea floor, and taking a wave train of first signals that represent acoustic impulses which are reflected from the layers of the earth below the sea floor are generated and displayed, characterized in that a) second signals (40 ') are recorded which represent the non-reflected wave train which caused by the primary and secondary expansion (s) (30 ', 34', 37, 38) b) an operator is created, which the curve shape the second signals (40 ') are converted into a preselected curve shape, and c) the first signals (24 ') are filtered with the operator so that output signals (24 "] that are a combination of signal components that arise from the primary and the (the) secondary expansions) with corresponding time shifts of the Components obtained is to have the effect of simultaneous occurrence of the primary and to achieve secondary expansion (s). 6. Device for performing the method according to claims 1-5, with an explosion triggering device for explosive charges to generate underwater explosions in the form of a rapidly expanding, high-pressure gas volume in the form of a gas bubble that passes through a charge is generated which is detonated at a depth that is sufficiently great to prevent the gas from entering the atmosphere immediately, the gas bubble in the Following the primary explosive expansion, collapses and expands again at least once, where the primary explosive expansion and the secondary expansion (s) are acoustic impulses, respectively that are reflected by layers of earth beneath the sea floor, and where a reflected wave train is generated by first signals representing acoustic impulses emitted by the said layers of earth are reflected, and with a pressure transducer device for displaying the reflected acoustic pulses, characterized in that at least one additional pressure transducer (40) is provided for generating second signals (40 ') which the non-reflected Represent the wave train caused by the primary and secondary expansion (s) (30 ', 34', 37 and 38) arises, and that a device (62, 72) for influencing an operator (60, 70) is provided is, the curve shape of the second signals (40 ') is converted into a preselected curve shape and the first Filters out signals (24 '), the operator generating output signals (24 "), the output signals which would have been generated in the absence of secondary expansion of the bladder. 7. Device according to claim 6, characterized in that the additional pressure transducer (40) is a Hydrophone is connected to the explosion release device, and that the hydrophone is the second signals (40 ') generated. 8. Device according to claim 7, characterized in that the device for creating the Operators (60 or 70) compress the waveform of the second signals (40 ') in time. 9. Device according to claim 8, characterized by the determination of the time interval between the primary expansion and a secondary expansion or secondary expansions, the Characteristic according to which the operator is created, a function of what is determined in this way Time interval is. 10. Device according to claim 9, characterized in that means for determining the ratios (a ^ aw a ^ law ...) of the amplitudes (ar, a ₃ ...) of secondary expansions relative to the amplitude (ai) of the primary expansion intended are, the characteristic according to which the Operator is a function of the ratios determined in this way in addition to the Is the time interval between the primary expansion and a secondary expansion The invention relates to a method for seismic prospecting underwater, in which a Underwater explosion is generated in the form of a rapidly expanding volume of gas under high pressure, in order to form a gas bubble at such a depth that the gas bubble is explosive in connection with the primary Expansion at least once collapses and expands again, with the primary explosive expansion and the secondary expansion (s) each generate an acoustic impulse from the layers of the earth below the ocean floor is reflected, and taking a wave train of first signals, the acoustic impulses represent, which are reflected by the layers of the earth below the sea floor, generated and displayed will. The invention also relates to a device for carrying out this method, having an explosion triggering device for explosive charges to generate underwater explosions in the form of a rapidly expanding, under high pressure, gas volume in the form of a gas bubble, which by a Charge is generated which is detonated to a depth sufficient to to prevent gas from entering the atmosphere directly, the gas bubble following the primary explosive expansion collapses at least once and expands again, the primary being explosive Expansion and the secondary expansion (s) each generate acoustic impulses from layers of the earth being reflected below the ocean floor, and being a reflected wave train of first signals is generated, which represents acoustic impulses that are reflected from the said layers of earth, and with a pressure transducer device for displaying the reflected acoustic pulses. In the technique of underwater seismic prospecting it is known that the acoustic energy resulting from the detonation of an explosive charge (or in general from a source of acoustic shock waves) is increased when the detonator, i. i.e., the source, is enclosed under pressure. For example, during seismic prospecting on land, a borehole is made in the Drilled earth, inserted a charge into the lower end of the borehole, and filled the borehole with sand, Filled with water or mud before detonating the explosive charge. The filling material works as embedding on the charge and completely increases the amount of energy converted into seismic energy significant, which is released by the detonation reaction. The seismic energy values used in the Soil transferred can be between embedded and non-embedded charge 50: 1 or more be. About the desired effect of increased, limited pressure in a seismic survey To achieve at sea, it is necessary to use explosive charges as sources of seismic energy at a sufficient depth detonate below the surface of the sea. The resulting gaseous explosion products result in an expanding bubble, creating a pulse of acoustic energy, which represents the seismic signal following the primary expansion, which is desirable, the gas bubble experiences an undesirable contraction Sequence of alternating secondary expansions and contractions, resulting in a generation of so-called "Bubble impulses", which are known in seismics. This phenomenon is detailed in the book "Underwater Explosion" by CoIe, published in In 1948 at Princeton University Press, and in US Pat. No. 2,622,691 each of these bubble impulses is explained in turn acts as a separate source of seismic energy, with the result that that of the body of The explosion sent the seismic signal a series of consecutive pulses instead of a single one Impulse, as this would be desired, represents. In order to avoid this effect during seismic exploration at sea, it has so far been customary to Detonating explosive charges as sources of seismic energy near the surface of the sea, so that the gaseous explosion products can escape directly into the atmosphere, and thereby preventing secondary expansions and contractions, i. H. Bubble impulses arise. There however, the arrangement of explosive charges in the water at a shallow depth below the sea surface The low water column necessarily results in a relatively weak embedment, such explosive charges make a relatively ineffective source of acoustic seismic signals Energy. As a result, in practice the use of Explosive charges at relatively great depths in the manner of seismic exploration by the Seismic refraction technology has been limited in which only the first arrival of an acoustic energy signal is looked at. In the seismic reflection technique, in which the entire sequence of reflected seismic Energy for the proper execution and final design of the survey and must be displayed, on the other hand, it was not possible to place the charges sufficiently deep below the Lower the sea surface while still achieving satisfactory results, namely on The reason for the complicated design of the reflected seismic energy signals produced by the successive secondary sequence of bubble signals caused by the successive Contractions and expansions of the gaseous explosion products are generated. A well-known method that has been able to eliminate the bubble impulse problem is the "Flexotir" method. (U.S. Patent 33 68 641). In this known method, the explosive charges are far below the Surface of water, but detonated in a perforated container that forms a cage. the Cage makes it possible that the primary shock wave is sent out by slowing down the subsequent one However, penetration of water into the cage will cause the initial bladder to collapse rapidly prevented. This known method works perfectly with relatively small charges, it however, relatively large cages are needed to cope with bubbles generated in front of relatively large charges suppress. In addition, the cage acts as a dampening device for the generated seismic Energy so that the usable portion of the energy