On: “Preferential continuation for potential‐field anomaly enhancement” (R. Pawlowski, GEOPHYSICS, 60, 390–398).

Geophysics ◽  
2001 ◽  
Vol 66 (2) ◽  
pp. 695-698 ◽  
Author(s):  
Hualin Zeng ◽  
Deshu Xu
Keyword(s):  
Gravity Anomaly ◽  
Potential Field ◽  
Common Method ◽  
Gravity Inversion ◽  
Observation Plane ◽  
Long Wavelength ◽  
Upward Continuation ◽  
Excellent Method ◽  
Deep Sources ◽  
Preferential Continuation

Pawlowski (1995) presents an excellent method for preferential continuation for potential‐field anomaly enhancement, and it is an appreciated attempt to solve a very common problem in gravity separation. Upward continuation of a gravity anomaly is a very common method for regional‐residual separation in China. One of the main problems in the conventional upward continuation is that it overattenuates regional‐field or useful long‐wavelength information due to deep sources. Sometimes attenuated‐upward continuation of an observed anomaly to a height has to be regarded as the original regional field at the observation plane in order to use gravity inversion to map deep interfaces such as the Moho. Application of the preferential continuation to gravity anomaly in some areas in China has shown very good effectiveness in solving the above problem (Xu and Zeng, 2000).

Preferential continuation for potential‐field anomaly enhancement

Geophysics ◽  
1995 ◽  
Vol 60 (2) ◽  
pp. 390-398 ◽  
Author(s):  
Robert S. Pawlowski
Keyword(s):  
Transfer Function ◽  
Potential Field ◽  
Short Wavelength ◽  
Amplitude Spectrum ◽  
Downward Continuation ◽  
Pass Filter ◽  
Long Wavelength ◽  
Upward Continuation ◽  
Deep Source ◽  
Preferential Continuation

A new class of filter transfer function derived from Wiener filter and Green’s equivalent layer principles is presented for upward and downward‐continuation enhancement of potential‐field data. The newly developed transfer function is called the preferential continuation operator. In contrast to the conventional continuation operator, the preferential continuation operator possesses a continuation response that acts preferentially upon a specific band of the observed potential field’s Fourier amplitude spectrum. The transfer function response approaches the response of an all‐pass filter away from this band. This response characteristic is useful for at least two common potential‐field signal enhancement applications. First, it is possible with preferential upward continuation to attenuate shallow‐source, short‐wavelength, potential‐field signals while minimally attenuating deep‐source, long wavelength signals (as often happens after application of conventional upward continuation) Second, it is possible with preferential downward continuation to enhance deep‐source, long wavelength signals without overamplifying shallow‐source, short‐wavelength signals (as often happens after application of conventional downward continuation) Preferential continuation, used qualitatively for anomaly enhancement, ably overcomes these two limitations of conventional continuation enhancement.

Reply by Author to the discussion by Ramesh Chander

Geophysics ◽  
1976 ◽  
Vol 41 (4) ◽  
pp. 777-778
Author(s):  
William R. Green
Keyword(s):  
Gravity Anomaly ◽  
Potential Field ◽  
Total Mass ◽  
Additional Constraint ◽  
Gravity Inversion ◽  
Inversion Method ◽  
Inversion Problem ◽  
Mass Excess

The nonuniqueness of potential field inversions makes it desirable to incorporate all available constraints into the inversion problem. Chander has correctly observed that the total mass excess (or defect) may be considered as a constraint in any gravity inversion method. Unfortunately, it does not provide an additional constraint to the gravity observations themselves, since the total anomalous mass is dependent on the gravity anomaly data.

A method for gravity anomaly separation based on preferential continuation and its application

2009 ◽  
Vol 6 (3) ◽  
pp. 217-225 ◽  
Author(s):  
Xiaohong Meng ◽  
Lianghui Guo ◽  
Zhaoxi Chen ◽  
Shuling Li ◽  
Lei Shi
Keyword(s):  
Gravity Anomaly ◽  
Preferential Continuation

Three-dimensional depth-to-basement modelling based on seismic and potential field data – basement configuration in the westernmost Polish Outer Carpathians

2020 ◽  
Author(s):  
Mateusz Mikołajczak ◽  
Jan Barmuta ◽  
Małgorzata Ponikowska ◽  
Stanislaw Mazur ◽  
Krzysztof Starzec
Keyword(s):  
Qualitative Analysis ◽  
Cross Sections ◽  
Potential Field ◽  
Field Data ◽  
Gravity Data ◽  
Three Dimensional ◽  
Magnetic Data ◽  
Gravity Inversion ◽  
Potential Field Data ◽  
Outer Carpathians

<p>The Silesian Nappe in the westernmost part of the Polish Outer Carpathians Fold and Thrust Belt exhibits simple, almost homoclinal character. Based on the field observations, a total stratigraphic thickness of this sequence equals to at least 5400 m. On the other hand, the published maps of the sub-Carpathian basement show its top at depths no greater than 3000 m b.s.l. or even 2000 m b.s.l. in the southern part of the Silesian Nappe. Assuming no drastic thickness variations within the sedimentary sequence of the Silesian Nappe, such estimates of the basement depth are inconsistent with the known thickness of the Silesian sedimentary succession. The rationale behind our work was to resolve this inconsistency and verify the actual depth and structure of the sub-Carpathian crystalline basement along two regional cross-sections. In order to achieve this goal, a joint 2D quantitative interpretation of gravity and magnetic data was performed along these regional cross-sections. The interpretation was supported by the qualitative analysis of magnetic and gravity maps and their derivatives to recognize structural features in the sub-Carpathian basement. The study was concluded with the 3D residual gravity inversion for the top of basement. The cross-sections along with the borehole data available from the area were applied to calibrate the inversion.</p><p>In the westernmost part of the Polish Outer Carpathians, the sub-Carpathian basement comprises part of the Brunovistulian Terrane. Because of great depths, the basement structure was investigated mainly by geophysical, usually non-seismic, methods. However, some deep boreholes managed to penetrate the basement that is composed of Neoproterozoic metamorphic and igneous rocks. The study area is located within the Upper Silesian block along the border between Poland and Czechia. There is a basement uplift as known mainly from boreholes, but the boundaries and architecture of this uplift are poorly recognized. Farther to the south, the top of the Neoproterozoic is buried under a thick cover of lower Palaeozoic sediments and Carpathian nappes.</p><p>Our integrative study allowed to construct a three-dimensional map for the top of basement the depth of which increases from about 1000 m to over 7000 m b.s.l. in the north and south of the study area, respectively. Qualitative analysis of magnetic and gravity data revealed the presence of some  basement-rooted faults delimiting the extent of the uplifted basement. The interpreted faults are oriented mainly towards NW-SE and NE-SW. Potential field data also document the correlation between the main basement steps and important thrust faults.</p><p> </p><p>This work has been funded by the Polish National Science Centre grant no UMO-2017/25/B/ST10/01348</p>

A method for inversion of 1D vertical soundings of gravity anomalies

Geophysics ◽  
2018 ◽  
Vol 83 (2) ◽  
pp. G15-G23
Author(s):  
Andrea Vitale ◽  
Domenico Di Massa ◽  
Maurizio Fedi ◽  
Giovanni Florio
Keyword(s):  
Potential Field ◽  
Field Data ◽  
Gravity Data ◽  
Finite Size ◽  
Gravity Anomalies ◽  
Real Data ◽  
Gravity Inversion ◽  
Chain Process ◽  
Potential Field Data ◽  
Gamma Density

We have developed a method to interpret potential fields, which obtains 1D models by inverting vertical soundings of potential field data. The vertical soundings are built through upward continuation of potential field data, measured on either a profile or a surface. The method assumes a forward problem consisting of a volume partitioned in layers, each of them homogeneous and horizontally finite, but with the density changing versus depth. The continuation errors, increasing with the altitude, are automatically handled by determining the coefficients of a third-order polynomial function of the altitude. Due to the finite size of the source volume, we need a priori information about the total horizontal extent of the volume, which is estimated by boundary analysis and optimized by a Markov chain process. For each sounding, a 1D inverse problem is independently solved by a nonnegative least-squares algorithm. Merging of the several inverted models finally yields approximate 2D or 3D models that are, however, shown to generate a good fit to the measured data. The method is applied to synthetic models, producing good results for either perfect or continued data. Even for real data, i.e., the gravity data of a sedimentary basin in Nevada, the results are interesting, and they are consistent with previous interpretation, based on 3D gravity inversion constrained by two gamma-gamma density logs.

Efficient gravity inversion of basement relief using a versatile modeling algorithm

Geophysics ◽  
2017 ◽  
Vol 82 (2) ◽  
pp. G23-G34 ◽  
Author(s):  
João B. C. Silva ◽  
Darcicléa F. Santos
Keyword(s):  
Gravity Anomaly ◽  
Region Of Interest ◽  
Sedimentary Basins ◽  
Density Contrast ◽  
Gravity Inversion ◽  
Deep Basin ◽  
Novel Approach ◽  
Green’S Operator ◽  
Translation Symmetry ◽  
Observation Position

We have developed a novel approach to compute, in an efficient and versatile way, the gravity anomaly produced by an arbitrary, discrete 3D distribution of density contrast. The method allows adjustable precision and is particularly suited for the interpretation of sedimentary basins. Because the gravity field decays with the square of the distance, we use a discrete Green’s operator that may be made much smaller than the whole study area. For irregularly positioned observations, this discrete Green’s operator must be computed just at the first iteration, and because each of its horizontal layers presents a center of symmetry, only one-eighth of its total elements need to be calculated. Furthermore, for gridded data on a plane, this operator develops translation symmetry for the whole region of interest and has to be computed just once for a single arbitrary observation position. The gravity anomaly is obtained as the product of this small operator by any arbitrary density contrast distribution in a convolution-like operation. We use the proposed modeling to estimate the basement relief of a [Formula: see text] basin with density contrast varying along [Formula: see text] only using a smaller Green’s operator at all iterations. The median of the absolute differences between relief estimates, using the small and a large operator (the latter covering the whole basin) has been approximately 9 m for a 3.6 km deep basin. We also successfully inverted the anomaly of a simulated basin with density contrast varying laterally and vertically, and a real anomaly produced by a steeply dipping basement. The proposed modeling is very fast. For 10,000 observations gridded on a plane, the inversion using the proposed approach for irregularly spaced data is two orders of magnitude faster than using an analytically derived fitting, and this ratio increases enormously with the number of observations.

On: “A case for upward continuation as a standard separation filter for potential‐field maps” by Bo Holm Jacobsen (GEOPHYSICS, 52, 1138–1148, August 1987)

Geophysics ◽  
1988 ◽  
Vol 53 (5) ◽  
pp. 723-723
Author(s):  
Nelson C. Steenland
Keyword(s):  
Cross Section ◽  
Potential Field ◽  
Thin Body ◽  
Thick Slab ◽  
Vertical Derivative ◽  
Upward Continuation ◽  
Original Field ◽  
First Vertical Derivative

This paper deals with gradients, not residuals. Computing a field up, then subtracting the “up” field from the original field to find residuals obviously involves shifting datums. Apparently the author got caught up in his equation (17) concerning the simple case of deriving the anomaly of a slab by subtracting the anomaly of one infinite prism from another of the same cross‐section but at a slightly smaller depth. That the anomaly of a slab behaves like the gradient (first vertical derivative) of the prism’s anomaly is apparent from the fact that the field of an infinitely thick slab attenuates by one power less than the field of a slab which approximates an infinitely thin body.

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