On the ambiguity of 4D gravity monitoring of geological media

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Veröffentlicht in:	Геофизический журнал
Datum:	2010
Hauptverfasser:	Dubovenko, Yu., Chorna, O.
Format:	Artikel
Sprache:	English
Veröffentlicht:	Інститут геофізики ім. С.I. Субботіна НАН України 2010
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spelling	Dubovenko, Yu. Chorna, O. 2016-06-02T14:26:48Z 2016-06-02T14:26:48Z 2010 On the ambiguity of 4D gravity monitoring of geological media / Yu. Dubovenko, O. Chorna // Геофизический журнал. — 2010. — Т. 32, № 4. — С. 41-46 . — Бібліогр.: 12 назв. — англ. 0203-3100 https://nasplib.isofts.kiev.ua/handle/123456789/101318 en Інститут геофізики ім. С.I. Субботіна НАН України Геофизический журнал On the ambiguity of 4D gravity monitoring of geological media Article published earlier
institution	Digital Library of Periodicals of National Academy of Sciences of Ukraine
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title	On the ambiguity of 4D gravity monitoring of geological media
spellingShingle	On the ambiguity of 4D gravity monitoring of geological media Dubovenko, Yu. Chorna, O.
title_short	On the ambiguity of 4D gravity monitoring of geological media
title_full	On the ambiguity of 4D gravity monitoring of geological media
title_fullStr	On the ambiguity of 4D gravity monitoring of geological media
title_full_unstemmed	On the ambiguity of 4D gravity monitoring of geological media
title_sort	on the ambiguity of 4d gravity monitoring of geological media
author	Dubovenko, Yu. Chorna, O.
author_facet	Dubovenko, Yu. Chorna, O.
publishDate	2010
language	English
container_title	Геофизический журнал
publisher	Інститут геофізики ім. С.I. Субботіна НАН України
format	Article
issn	0203-3100
url	https://nasplib.isofts.kiev.ua/handle/123456789/101318
citation_txt	On the ambiguity of 4D gravity monitoring of geological media / Yu. Dubovenko, O. Chorna // Геофизический журнал. — 2010. — Т. 32, № 4. — С. 41-46 . — Бібліогр.: 12 назв. — англ.
work_keys_str_mv	AT dubovenkoyu ontheambiguityof4dgravitymonitoringofgeologicalmedia AT chornao ontheambiguityof4dgravitymonitoringofgeologicalmedia
first_indexed	2025-11-26T20:16:07Z
last_indexed	2025-11-26T20:16:07Z
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fulltext	�� !"#�$%&'�("�%()�#+#�' #(&"�&��&,#��-�%()� �)#..'(/ On the ambiguity of 4D gravity monitoring of geological media © Yu. Dubovenko, O. Chorna, 2010 Institute of Geophysics, National Academy of Sciences of Ukraine, Kiev, Ukraine dubovenko@igph.kiev.ua The main concept of 4D gravity monitoring being realized on the short profiles is in common supplied by the analitical relations with the rapidly decreasing kernels. The monitoring perceptible depends on the non-tidal quasiperiodic variation of gravity field and also is influenced by the low-level geophysical fac-tors marked out by the Dvulit’s techniques� 1. On the background of monitoring. Now on the amount, methods and opportunity to execute large-scale geophysical workings affect both the increasing accuracy and productivity of gravity sur-veying (this method at acceptable accuracy remains affordable prospecting and exploration solution due to improved equipment and GPS support) and a markedly sharp decline in volume measurements. The first trend cause to review the methods of pro-cessing of the data acquired, in particular, a more accurate account of a Bouguer corrections [Bychkov, 2007]. The latter one, due to need of detection a de-eper sources of anomalies1 , entails the revision of the / The possibilities of regularization methods in solving the problems of building complex cross sections at the present level of model representations on the geological environment are close to the technological limit. measurement method to account for subtle features of gravity anomalies without complicating the mathe-matical apparatus, measurement techniques and in-creasing the logistical costs. These features one can "hooks" wit the help of additional variable — the time. In this regard, the world's "trends" of geophysi-cal observations gradually tend to the continuous 4D monitoring (Geophysics. — 2008. — 73� � 6) of studied area, studying the evolution of the gravity field during exploitation time of the area or over du- ration of interval of his abrupt dynamic activation. Nevertheless in the English-speaking sources the term "gravity variations" means temporal diffe-rence between the real anomalies in limited spa-ces, which sources are the objects with the rapidly changing of deep dynamics, while in the USSR’s literature this concept are reserved for a weak qua-si-periodic fluctuations in the super-long profiles crossing the area of contrasting modern vertical movements of Earth's crust. /#�)-(% '0%.�+,#(� #(%1 �� But the idea of monitoring the some of its appli- cations illustrate the work [Bolotnova, 2007]. Ne- vertheless, in these sources there are no mention on the background of monitoring — the gravity vari- ations in the sense laid in the [Sobakar, 1972] and on their dependence on a series of low-level natural and man-made factors. The use of repeated observations in a certain region in gravimetry branch is comparatively well known (its elements are used in the creation of re- gional density models of the Caucasus, in [Alek- sidze, 1985], also [Yurkina, 1978]), although con- tinuous in time to call them rather difficult, whereas in seismometry this for a long time there is a com- mon practice. However, the organization of any high- precision measurements with the gravity as a se- parate parameter, its variational component should always be investigated to take into account. 2. On the variations of gravity. For the first time in the USSR’s literature a various components of vari- ation part of the gravity field are examined and a non- tidal quasi-periodic variations (QPV) of gravity (with amplitude within 3 to 5 times the measurement error) are picked out in [Sobakar, 1972]. For aim of their measurement was created a new triple basis. The methodological one means a use of the heterogeneous Earth model as in a physical-chemical as in a energy- efficient treatment. The methodological one relies on the fact that QPV have maximum at the intersection of tectonic structures of different ages and in the areas of contrasted modern vertical movements. The metrological one relies upon the observations on the network with optimal density and configuration by the multiple devices with a high coefficient of reliability and comparison of QPV gradients and the observed gra- vity anomalies. The QPV itself obviously are closely related to endogenous processes of formation and develop- ment of density inhomogeneities of the Earth’s crust and mantle, although not confined by them. The Earth's moment of inertia is changing during the redistribution of matter inside it, and as a consequence — the rotation regime and the corres- ponding gravity. Equilibrium Figure of the Earth is disturbed in the process of the redistribution, chan- ging the gravity intensity. During isostatic restora- tion of the equilibrium patterns gravity changes once again. The range of processes mentioned genera- tes the QPV gravity of the Earth. The reversible part of the process thus creates a periodic part of varia- tion, and the irreversible part — a non-periodic part of the variations, which forms a stationary gravity anomalies. There are correlation of large-scale mantle den- sity inhomogeneities and tidal parameters of Earth, characterizing its tidal deformation. Earth tidal pa- rameters (Love and Shida numbers) are based on the calculation of the relaxation amplitudes of grav- ity potential on the Earth surface and in its nucleus. Thereby a cross-correlation of QPV and the referred dynamic parameters of the Earth may be exist. This fact requires a separate studying. Despite a low-intensity, anomalies of QPV gravi- ty can be identified with confidence due to the pe- culiarities of the behavior of QPV curve time and the close inverse proportional correlation with the curves of vertical crustal movements. The latter one [So- bakar, 1972] is considered the result of com- monness of processes in the upper mantle, affect- ing the QPV and the vertical movements. The total value of the QPV is treated as the sum of superpo- sitions of variations of different origin, sign, period and amplitude. This total amplitude ultimately de- termines the evolution of Earth's gravity field caused by the evolution of the inhomogeneities of the crust and upper mantle. 3. The basis of monitoring. We call the gravi- tational monitoring a series of periodically repeated real-time continuous for a fixed period (Fig. 1) mic- rogravity measurements and its processing subject to the influence of environment and area of applica- tion. Fig. 1. 11-day series of measurements of gravity force: a — without filtering, b — with bandpass filtering, c — with cor- rection for tidal effects. �� !"#�$%&'�("�%()�#+#�' #(&"�&��&,#��-�%()� �)#..'(/ The magnitude of the time interval depends on the quality of measurements, the measure of un- certainty of the observation data, the dynamics (am- plitude and frequency) of the gravity. Continuous connection of dynamics of the gravi- ty and the environment parameters is the physical basis of gravity monitoring: thus to the undulations of the centimeter range are satisfied the gravity vari- ations in a few mGal. If the deformation of surface relief of a certain area there is a direct consequence of the surface mass distribution, then gravity moni- toring can be used to study a decompaction and fluid regime of the area studied. The spatial distribution of variations of the verti- cal derivative values Vz of the gravity potential di- rectly correlates with the area distribution of densi- ties and temporal variations of Vz values clearly de- fine the vertical variations of the fluid saturation. Hardware base of the monitoring are a joint large- scale measurements of the terrain elevations by the GPS data and an absolute gravity values (hundreds of point on hundreds of km2). The cheaper relative gravity measurement has serious limitations — the binding to the reference grid and the necessity for simultaneous accounting >zero creep?. Neverthe- less, in our case such measurements with proper methodical maintenance have the greatest pros- pect. A continuous measurements of gravity in boreholes may be used at some areas, as prevai- ling in the resolution that of the ground surveys due to the greater proximity to the disturbing sources and the elimination of surface effects. Some developments from the instrumental base of the marine gravimetry is advisable for use to compensate the influence of tem- perature and the other external factors. 4. On the extraction of a weak signal. In case studies of the 4D gravity monitoring (Geophysics, 2008. — 73� � 6), the amplitudes of the signal are within the range of 20 mGal to 80 mGal. Within the boundaries of the active volcanoes of the signal amplitude increases to 300—600 mGal, and within watersheds ~200—250 mGal under a nonlinear accounting of "zero creep". Due to the repeated- ness of measurements, fixing the residual gravity values at the observation point, we can estimate the accuracy of definition of the wanted signal in the time interval. With the aim to extract a weak signal within the background noise in the gravimetry the methods of correlation analysis and calculation of some com- ponents of the gradients by the direct measure- ments of gravity are applied2 . The signal wanted has distinguished by calculating the difference ano- malies wzmd gghgg def , where — the difference between 2 adjacent time samples, — a free air correction, hz — a vertical displace- ment; gdef — a Bouguer anomaly of deformation3 ; zzww Gg 422 — the impact of ground- water. Also the additional connection to indepen- dent observations at a reference point located near the investigated area is used. $ �� 4!�� 9 �� @��; � �� ;� �� 9�� 99�� 9 �� 4!�� 9�� 4 @� � 9�AA� �� B$��ó� C�� 2004]. If there is lack of length of series observa- tions, may be useful a low-order polynomial ap- proximation with the appropriate "calibration" of the polynomial order. Besides, there is advisable the comparing of the filtering results with the data ob- tained from a nearby checkpoint from the area of observations. As in the case of the QPV gravity measurements, there are (Geophysics, 2008. — 73� � 6) noted the correlation of a weak signal with vertical shifts. Assuming the different frequency of gravity strength and noise variations it is used a frequency filtering to enhance the signal wanted. The analogy can be seen again in the marine gravimetry. In the plain terrain areas the signal has a small gradient, and this approach, in our opinion, is ineffective. In such case the impact of noise must be considered in other ways — by the changing the geometry of ob- servation networks, with the help of the temporal filtering, the derivatives calculation, and so on, as mentioned in [Sobakar, 1972]. 5. On the method of monitoring. To organize the monitoring in it’s methodical way, perhaps, is best as in [Sobakar, 1972], and to study the metro- logy nuances on the geodynamic polygon with a set of geophysical measurements. Lack of infra- structure and equipment will significantly influence on the costs of monitoring at the landfill — its in- creases by the uncertain value. The using of a digital recording will avoid some difficulties in the early sta- ges of surveying by simplifying the scheme of survey- ing and also it accelerates the creation of a digital model of the object. To overcome the financial and technological deadlock we see in the cooperation of different institutions with common usage of equip- 3 Just as in the marine gravimetric surveying are applied the calculation of the vertical and horizontal gradients of gravity and their complex interpretation. This method of interpreta- tion is tested on offshore oil-gas structures [Yurgin, 2006]. * Contribution from changes in volume due to compression of environment around the disturbing source, which implies the displacement of density boundaries in a heterogeneous en- vironment. /#�)-(% '0%.�+,#(� #(%1 �� ment, personnel, methods and the common over- view of the research on the common object4 . The application of the classical scheme of mea- surements on a regular network of points and the sub- sequent recalculation of the gravity values by the well- known Poisson integral is suitable for regional studies (Geophysics. — 2008. — 73, � 6), but in the local conditions, often used for gravity monitoring [Bolotno- va, 2007], it has a number of shortcomings [Duboven- ko, 2002]. Besides, sometimes for many reasons the organization of regular network is impossible, and the conversion from an irregular network on a regular ba- sis is more complex task than the inversion of the geological media structure from data measured. A solution of the inverse problems of gravimetry with data given on a pseudo regular network with using the environmental models such as "endless profile" leads to ill-conditioned systems of linear equations, generating meaningless results. Because of this, and to proceed from mostly short length of the actual measurement profiles, it is expedient an alternative approach. To interpret the measurements on the short pro- files is proposed [Dubovenko, 2002] the system of the linear integral equations with rapidly decreasing kernels: xSn 1 xSd x x S x xv n n n n 1 2 cosh 2 1 , xSn 1 xSd x x S x xv n n n n 1 2 tanh 2 1 , xvxSxSx 000 , xSxSx 000 , ,0n . With the account of the above the method of [Bolotnova, 2007] is effective only in certain condi- tions (a regional background is a polynomial of 1-st degree; there are known the densities and positi- ons of the boundaries of gravitating bodies on the surface, and these bodies are similar or have a com- mon contacts). It implies in particular the construc- tion of a spatial density model of the medium divi- ded into 3 stages: the separation of gravity sources anomalies and the identification of effective depths of their occurrence and the quasidensity (zero ap- proximation), then the detection of true depths and densities of disturbing bodies by the solution of the 2D inverse problem (1-st approximation) and the fi- nal solution in the ADG-3D package. We propose in the method [Bolotnova, 2007] to use the software [Starostenko et al., 2004] and the prog- ram kit obtained in the PhD study [Dubovenko, 2002]. 6. On the interpretation of data. The purpose of monitoring is to assess the depth of the source of anomalies and the changes of the volume ac- cording to the deformation data of the relief. It re- quires a knowledge on the surface mass distribu- tion (from the gravity data). Deformations of the earth surface are received by the GPS data, having a se- ries of advantages over traditional surveying me- thods5 . Near-surface heterogeneities of the medi- um structure (as karsts, baird, areas of flooding and loosening), the complex structure of the area (fol- ding, salt tectonics, faults), the factors of the ab- sorption of wanted signal (the temperature, the in- strumental effects) are limiting the efficiency of mon- itoring, without reducing its practical value. In (Geophysics, 2008. — 73� � 6) does not take into account the peculiarity of the gravity variations: a fluctuations in the value of its derivatives depend on the fluctuations of the low-level geophysical events (as anomalous atmospheric masses (Fig. 2), , This way of the integrated monitoring (a collaborative gra- vity network) comes well many western companies. - The independence from the time of day and the weather conditions, the automation, the continuity, the completeness, the reliable binding to the network. Fig. 2. Western Ukraine gravity change as a result of move- ment of air masses [Dvulit, 1999]. �� 4 �� !"#�$%&'�("�%()�#+#�' #(&"�&��&,#��-�%()� �)#..'(/ the snow masses, the groundwater level, forest co- ver and changes in topography (Fig. 3) due to an- thropogenic activities. We can take into account these effects through the entering corresponding corrections [Dvulit, 1999] into the solution of direct problems of gravimetry in the areas of study (it is assumed that due to long-term monitoring period of station is known the structure beneath the area). Fig. 3. Western Ukraine gravity changes as a result of mass transfer in the subsurface area [Dvulit, 1999]. The unjustified simplification of the analytical models of the geological media with the aim to re- duce the ambiguity of interpretation in many cases may be the cause of incorrect results of calcula- tions of the geometry sources and the vertical and lateral distribution of the density inhomogeneities. This especially takes place in cases where the ex- ternal environment around the anomalous source is far from the assumptions of homogeneity. Reliable quantitative interpretation of the dynamics of the masses, for example, in the case of monitoring of hydrocarbons deposits can be produced providing the well-known geometry of the gravitating bodies (by the seismic data) and by the integrated interpretation of gravity field and deformation of re- lief data. To avoid the ambiguity mentioned the the maxi- mal accounting of the given a priori information about the media studied is needed. We propose to carry out it in 2 reciprocal supplementary ways: 1) by the constructing an appropriate model con- cepts (star-shape domains of known density inside the compact sets in the Banach space data); 2) by the adding into the discrepancy functio- nals in regularizing algorithms for some stabilizers of differential form, which eigenfunctions coincides with the eigenfunctions of the initial operators. The section1 is justified in [Dubovenko, 2002], while section 2 — in [Chorna, 1999]. The solution of the specific inverse problems by the regularization is advisable by the algorithms of [Regularizing..., 1983] and similar one — on the basis of [Duboven- ko, 2002; Starostenko et al., 2004]. 7. Conclusions. The reasons considered above for gravity monitoring leads to next general issues. The QPV of gravity should be taken into account in interpreting the results of 4D gravity in order to introduce appropriate corrections to the gravity sur- veys of different ages, to the long-term precision topographic mapping, to the clarifying the rheology of the investigated area, etc. The weak signal must be extracted from noise by the geometry control of observation networks, by the temporal filtering or the derivatives calcula- tion. The measurements data interpretation on the short profiles give best results with the system of the linear integral equations with rapidly decreasing kernels being incorporated into existing 2D inver- sion. The monitoring data must be corrected for the impact of fluctuations of the low-level geophysical events by the [Dvulit, 1999] technique. An a priori information about the geological me- dia may be accounted both by the selection of an appropriate media model and the special correction of regularization algorithms for ill-posed problems. Repeated measurements of the gravity has a variety of applications but after the correction of the monitoring technique the results can be extended into the branch of QPV usage specified in [Sobakar, 1972]. The steps above seems to be necessary but maybe not sufficient to reduce the ambiguity of gra- vity monitoring interpretation. An experimental con- firmation is expected. From the gravity inversion of the monitoring data one can establish the basic image of density va- riations6 not the absolute density values. There are great prospects for the interpretation of the tempo- ral variations of gravity anomalies arising from chan- ges of water-oil contact, or the level of reservoir wa- ter in the depths or any wells. It can be used as an inexpensive way of gravity monitoring of undergro- und ecosystem of megapolises and the other geo- ecological solutions (the tracing the effects of floods, the landslides, the dynamics of pollution of under- ground basins, etc.). . A decreasing of g stands for a decrease of hydrocar- bons volume due to their production and thus, the lowering of gas-oil contact, but the increasing g stands for raising the level of the water layer of formation. /#�)-(% '0%.�+,#(� #(%1 �5 �� References tors on the variation of the gravity field of the Earth. — F. Dr. theses in Engineer. Sci: 05.24.01. Lviv Poly- technical. — Lvov, 1999. — 225 p. (in Ukrainian). Regularization algorithms and a priori information / Eds. A. N. Tikhonov, A. V. Goncharsky, V. V. Stepanov, A. G. Yagola. — Moscow: Science, 1983. — 200 p. Sobakar G. T. Quasiperiodic variations of the gravity field of the Earth, their nature and applied scientific value // Geophys. Proceedings AS USSR. — 1972. — 46. — P. 31—42 (in Russian). Starostenko V. I., Legostaeva O. V., Makarenko I. B., Pavlyuk E. V., Sharypanov V. M. On the automat- ed input into a computer the images of the geolog- ical and geophysical maps with gaps of 1 st kind and the interactive visualization of 3-D geohysical models and their fields // Geophys. J. — 2004. — 26� �/� 0 �� 0/* <�� %� ��=� Yurgin O. V. High-precision gravity prospecting for measurement of gravitational effects of shallow ori- gin: Thesis for a cand. degree on engineer. sci. — Perm, 2006. — 26 p. (in Russian). Yurkina M. I� ��9�� 9 4�� 4�� 9 �� 9�� 4��4�� !�� 4� �� ++ �� C�� !�� 0 /271� 0 �)),� 0 ��))60- (in Russian). Aleksidze M. A. The solution of some fundamental problems of gravimetry. — Tbilisi: Metsniereba, 1985. — 412 p. (in Russian). ��ó��., �� . $ � �� 9�AA� �� 4 � �� 9�� 99�� 9 4� �� !��4� �� // Phys. Earth Planet. Int. — 2004. — 142. — P. 37—47. Bolotnova L. A. Eco-geological study of the state of geological environment in urban areas: geophysi- cal aspects / V. V. Filatov, L. A. Bolotnova // IX Geo- phys. readings after V. V. Fedynskiy, 1—3 March 2007: Abstr. proceedings. — Moscow, 2007. — P. 43—44 (in Russian). Bychkov S. G. On the calculation of gravity anomaly in the Bouguer reduction // IX Geophys. readings after V. V. Fedynskiy, 1—3 March 2007: Abstr. pro- ceedings. — Moscow, 2007. — P. 73—77. Chorna O. A. Investigation of inverse problems of the logarithmic potential theory for bodies resembling the given ones: Thesis for a cand. degree on phys.- mat. sci. / National Academy of Sciences of Ukraine. — Kiev, 1999. — 26 p. (in Russian). Dubovenko Yu. I. Restoration of the contact bound- ary in layered medium // Geophys. J. — 2002. — 24� �)).� 0 ��))*.0,/ (in Ukrainian). Dvulit P. D. Methods of accounting of geophysical-

On the ambiguity of 4D gravity monitoring of geological media

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