Microgravimetric and gravity gradient techniques for detection of subsurface cavities

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 1084-1096 ◽  
Author(s):  
Dwain K. Butler
Keyword(s):  
Case History ◽  
Vertical Gradient ◽  
Gravity Gradient ◽  
Horizontal Gradient ◽  
Shallow Subsurface ◽  
Gradient Profile ◽  
First Case ◽  
Profile Line ◽  
Cavity System ◽  
Subsurface Cavities

Microgravimetric and gravity gradient surveying techniques are applicable to the detection and delineation of shallow subsurface cavities and tunnels. Two case histories of the use of these techniques to site investigations in karst regions are presented. In the first case history, the delineation of a shallow (∼10 m deep), air‐filled cavity system by a microgravimetric survey is demonstrated. Also, application of familiar ring and center point techniques produces derivative maps which demonstrate (1) the use of second derivative techniques to produce a “residual” gravity map, and (2) the ability of first derivative techniques to resolve closely spaced or complex subsurface features. In the second case history, a deeper (∼ 30 m deep), water‐filled cavity system is adequately detected by a microgravity survey. Results of an interval (tower) vertical gradient survey along a profile line are presented in the second case history; this vertical gradient survey successfully detected shallow (<6 m) anomalous features such as limestone pinnacles and clay pockets, but the data are too “noisy” to permit detection of the vertical gradient anomaly caused by the cavity system. Interval horizontal gradients were determined along the same profile line at the second site, and a vertical gradient profile is determined from the horizontal gradient profile by a Hilbert transform technique. The measured horizontal gradient profile and the computed vertical gradient profile compare quite well with corresponding profiles calculated for a two‐dimensional model of the cavity system.

scholarly journals Generalized gravity gradient analysis for 2-D inversion

Geophysics ◽  
1995 ◽  
Vol 60 (4) ◽  
pp. 1018-1028 ◽  
Author(s):  
Dwain K. Butler
Keyword(s):  
Gravity Data ◽  
Vertical Gradient ◽  
Diagnostic Information ◽  
Effective Density ◽  
Gravity Gradient ◽  
Horizontal Gradient ◽  
Plate Model ◽  
Structural Interpretation ◽  
Gradient Profile ◽  
Inversion Procedure

Gravity gradient profiles across subsurface structures that are approximately 2-D contain diagnostic information regarding depth, size, and structure (geometry). Gradient space plots, i.e., plots of horizontal gradient versus vertical gradient, present the complete magnitude and phase information in the gradient profiles simultaneously. Considerable previous work demonstrates the possibility for complete structural interpretation of a truncated plate model from the gradient space plot. The qualitative and quantitative diagnostic information contained in gradient space plots is general, however. Examination of the characteristics of gradient space plots reveals that 2-D structures are readily classified as extended or localized. For example, the truncated plate model is an extended model, while the faulted plate model is a localized model. Comparison of measured or calculated gradient space plots to a model gradient space plot catalog allows a rapid, qualitative determination of structure or geometry. “Corners” of a polygonal cross‐section model are then determined as profile points corresponding to maxima on the vertical gradient profile. A generalized approach to structural interpretation from gravity data consists of (1) determining vertical and horizontal gradient profiles perpendicular to the strike of a 2-D gravity anomaly, (2) determining the structural geometry from the gradient space plot, and (3) locating profile positions of structural corners from the vertical gradient profile. This generalized inversion procedure requires no quantitative information or assumption regarding density contrasts. Iterative forward modeling then predicts the density contrasts. Application of this generalized gravity gradient inversion procedure to high quality gravity data results in an effective density prediction consistent with measured near‐surface densities and the known increase in density with depth in deep sedimentary basins.

scholarly journals Subsurface Cavity Detection Using Electrical Resistivity Tomography (Ert); A Case Study from Southern Quetta, Pakistan

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Syed Ali Abbas ◽  
Muhammad Saeed ◽  
Mukhtiar Ghani ◽  
Taseer Ahmad
Keyword(s):  
Electrical Resistivity ◽  
Fracture Zones ◽  
Resistivity Tomography ◽  
Cavity Detection ◽  
Building Collapse ◽  
Profile Line ◽  
Tomographic Method ◽  
Cavity System ◽  
Subsurface Cavities

AbstractDipole-dipole electrical resistivity tomographic method was applied to investigate the subsurface cavities at Staff Welfare Hospital & School Quetta. A total of 890-meter profile line was covered along five smaller profile lines and fracture zones with maximum 21 meters interval. The cavity system along profile line-1 and 2 was very restricted and had no direct impact on infrastructure while major cavity beneath the building was traced at profile line-3 and line-4 thus constituting a ~20m wide cavity system with 3-4 small interconnected cavities between depths of 7 to 21 meters. This system was also traced at profile line-4 at a depth of 10 meters having a reduced width of 10m. At profile line-5, a few other cavities were detected that proved imperceptible due to limitations in data acquisition. To conclude, the cavity systems traced in profile line-3 and profile line-4 were the most perilous ones and are commonly the foremost reason for building collapse.

Advantages of using the vertical gradient of gravity for 3-D interpretation

Geophysics ◽  
1993 ◽  
Vol 58 (11) ◽  
pp. 1588-1595 ◽  
Author(s):  
I. Marson ◽  
E. E. Klingele
Keyword(s):  
Gravity Data ◽  
Vertical Gradient ◽  
Three Dimensions ◽  
Gravity Gradient ◽  
Horizontal Gradient ◽  
Euler Deconvolution ◽  
Model Studies ◽  
Combined Use ◽  
Deconvolution Techniques ◽  
Vertical Gradient Of Gravity

Gravity gradiometric data or gravity data transformed into vertical gradient can be efficiently processed in three dimensions for delineating density discontinuities. Model studies, performed with the combined use of maxima of analytic signal and of horizontal gradient and the Euler deconvolution techniques on the gravity field and its vertical gradient, demonstrate the superiority of the latter in locating density contrasts. Particularly in the case of interfering anomalies, where the use of gravity alone fails, the gravity gradient is able to provide useful information with satisfactory accuracy.

Who Was the ‘Heroine’ of Freud's First Case History? Problems and Issues in the Identification of Freud's patients

2017 ◽  
Vol 19 (1) ◽  
pp. 7-54 ◽  
Author(s):  
Richard Skues
Keyword(s):  
Case History ◽  
The Real ◽  
Hypnotic Suggestion ◽  
Social Circle ◽  
First Case ◽  
The Face ◽  
Historical Investigation

In 1892–3 Freud published his first substantial case history, which concerned a patient treated by means of hypnotic suggestion. For some years this has been one of the few remaining of Freud's dedicated cases histories where the patient has not been identified. More recently, however, two publications independently arrived at the conclusion that the patient was none other than Freud's wife, Martha. This paper sets out the reasons why this identification should always have been treated with suspicion, even if the real identity was not known. Nevertheless, the paper goes on to offer a more plausible identification from among Freud's known social circle. The second part of the paper questions the circumstances under which the original misidentification could plausibly have been sustained in the face of such glaring evidence to the contrary. It concludes that, among other reasons, recent tendencies in controversies about Freud's trustworthiness have the hazard of leading to unreliable assumptions about Freud's honesty being taken as a basis for sound historical investigation.

Development and Applications of a Wellhead Protection Area Delineation Computer Program

1991 ◽  
Vol 24 (11) ◽  
pp. 51-62 ◽  
Author(s):  
N. Guiguer ◽  
T. Franz
Keyword(s):  
Case History ◽  
Numerical Models ◽  
Groundwater Resources ◽  
Theoretical Background ◽  
Human Interaction ◽  
Wellhead Protection ◽  
First Case ◽  
Protection Area ◽  
And Storage ◽  
The Town

In the last few years, groundwater management has concentrated on the protection of groundwater quality. An increasing number of countries has adopted policies to protect vital groundwater resources from deterioration by regulating human interaction with the subsurface, the use of potential contaminants, land use restrictions, and waste transport and storage. One of the more common regulatory approaches to the protection of groundwater focuses on public water supplies to reduce the potential of human exposure to hazardous contaminants. Under the framework of the Safe Drinking Water Act amended by U.S. Congress in 1986, The U.S.EPA (1987) issued guidelines for the delineation of wellhead protection areas, recommending the use of analytical and numerical models for the identification of such areas. In this study, the theoretical background for the development of one such numerical model is presented. Two real-world applications are discussed: in the first case history, the model is applied to a Superfund Site in Puerto Rico as a tool for assessment of the effectiveness of a proposed pump-and-treat scheme for aquifer remediation. Based on simulation results for the evolution of the existing contaminant plume it was verified that such a scheme would not work with the proposed purging wells. The second case history is the delineation of a wellhead protection area in the Town of Littleton, Massachusetts, and subsequent design of a monitoring well network.

A first case history

2016 ◽  
pp. 37-51
Author(s):  
R. Peter Hobson
Keyword(s):  
Case History ◽  
Clinical Material ◽  
Initial Assessment ◽  
Psychoanalytic Therapy ◽  
First Case ◽  
Transference And Countertransference ◽  
History Of

The purpose of this chapter is to introduce Brief Psychoanalytic Therapy through the case history of a woman who presented with fatigue and a variety of medical ailments. Descriptions are given of the initial assessment consultation and then the course of 16 sessions of Brief Psychoanalytic Therapy. The clinical material represented illustrates both the therapist’s orientation and style of intervention, and the patient’s step-by-step development in the direction of more open, trusting, and fulfilling attitudes toward other people and the possibilities of life. The nature as well as the influence of the therapist’s focus on the transference and countertransference receive special attention.

First Case History

1959 ◽  
Vol 39 (1) ◽  
pp. 18-20
Author(s):  
Martin O. Mundale
Keyword(s):  
Case History ◽  
First Case

VERTICAL GRADIENT OF GRAVITY ON AXIS FOR HOLLOW AND SOLID CYLINDERS

Geophysics ◽  
1966 ◽  
Vol 31 (4) ◽  
pp. 816-820 ◽  
Author(s):  
Thomas A. Elkins
Keyword(s):  
Hollow Cylinder ◽  
Sudden Change ◽  
Vertical Gradient ◽  
Outer Radius ◽  
Gravity Gradient ◽  
Gradient Effect ◽  
Vertical Gravity Gradient ◽  
Vertical Gravity ◽  
Special Case ◽  
Vertical Gradient Of Gravity

The recent interest in borehole gravimeters and vertical gravity gradient meters makes it worthwhile to analyze the simple case of the vertical gravity gradient on the axis of a hollow cylinder, simulating a borehole. From the viewpoint of potential theory the results are interesting because of the discontinuities which may occur when a vertical gradient profile crosses a sudden change in density. Formulas for the vertical gradient effect are given for observations above, inside, and below a hollow cylinder and a solid cylinder. The special case of an infinitely large outer radius for the cylinders is also considered, leading to formulas for the vertical gradient effect inside a borehole on its axis and inside a horizontal slab. Some remarks are made on the influence of the shape of a buried vertical gradient meter on the correction factor for changing the meter reading to density.

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