- Home
- A-Z Publications
- Geophysical Prospecting
- Fast Track Listing
Geophysical Prospecting - Online First
41 - 60 of 92 results
-
-
Constrained 1D joint inversion of seismic surface waves and P‐refraction traveltimes
Authors C. Piatti, L.V. Socco, D. Boiero and S. FotiAvailable online: 15 May 2012More LessABSTRACTWe present a joint inversion scheme that couples P‐wave refraction and seismic surface‐wave data for a layered subsurface. An algorithm is implemented with a damped least‐squares approach. The estimated parameters are S‐ and P‐wave velocities and layer thicknesses, while densities are assumed constant during inversion. The coupling is both geometric and physical: layer thicknesses are the same for S‐ and P‐wave velocity profiles and P‐wave velocities enter in both forward algorithms. Sensitivity analysis, performed on synthetic data, reveals that surface‐wave dispersion curves can be sensitive also to P‐wave velocity of some layers (especially for Poisson's ratio values smaller than about 0.35), allowing synergic resolution of this parameter. Applications on both synthetic and field data show that the proposed approach mitigates the hidden layer problem of seismic refraction and leads to more accurate results than individual inversions also for surface waves. Additional constraints on the objective function on a priori Poisson's ratio values allow unrealistic and not admissible VP and VS values to be avoided; such constraints were applied in one field case considering the a priori information available about water‐table depth. It is also shown that estimation of porosity can help the selection of the proper constraint on a priori Poisson's ratio.
-
-
-
-
-
THREE DIMENSIONAL GRAVITY SURVEY*
By W. DOMZALSKIAvailable online: 09 October 2008More LessABSTRACTThe paper describes and discusses the results of an experimental gravity survey which was carried out underground on different levels of a mine, in the mine shafts, and on the surface above the mine workings.
The paper is composed of three complementing sections. The part dealing with gravity measurements in the shafts gives also attention to the particular problem of the terrain corrections underground, due to the surface topography. The interval densities from gravity measurements in the shafts are computed and adjusted in accordance with known geology and compared with the stratigraphical columns of the shafts. The effect of the ore body on the stations in the shaft is derived theoretically and compared with the observed one.
The gravity contours are constructed on different levels in the mine workings and discussed in relation to the known extent of the ore body. The gravity profile across a fault underground is presented and discussed. Another gravity profile was run underground in the same plan position as a surface traverse 1000 feet above it. The line of boreholes along this traverse gives good account of geology which includes step‐faulting. This known geology is compared with the deductions based on the gravity results. This is also done in the case of another gravity profile run over a known geological section. A number of gravity measurements were also taken in the same plan position, separated by the vertical distance of 800–1,100 feet. These points were placed by the boreholes previously drilled in the area. Attempt in correlation of these and gravity results is made.
The densities computed from the gravity measurements are compared with the laboratory determinations of the densities, carried out on samples from different parts of the mine.
The contours on the top of the base formation are constructed from the information obtained from the boreholes, and are compared with the gravity contours on the surface above.
A simple method of computation of the effects of slabs and blocks is presented as applied to the calculation of the corrections for underground drifts and faults. A table is appended for use with this method.
-
-
-
DRILLING METHODS IN SAND AND GRAVEL FORMATIONS*
By G. MURATORIAvailable online: 09 October 2008More LessABSTRACTIn the development of seismic drilling methods in Northern Italy the most important considerations have been those of ease in transport and quickness of operation. Different drilling systems are described that are adapted to the different types of near surface formation that are encountered in the area. In soft sands a high pressure water jet is used, a rotary table not being required in a great many cases. In medium consistency sand and small gravel, the drill rods are rotated by a special roller wrench equipment instead of the more usual kelly. In coarse formations, gravel and boulders, casing is driven by special pile driving equipment with collapsible mast for easy transport.
-
-
-
SOME THEORETICAL CONSIDERATIONS ON THE USE OF MULTIPLE GEOPHONES ARRANGED LINEARLY ALONG THE LINE OF TRAVERSE*
Authors F. W. HALES and T. E. EDWARDSAvailable online: 09 October 2008More LessAbstractAn analytical treatment is given of the response of linear arrays of multiple geophones, as a function of the direction of incidence of the wave and of the wave frequency. The relation between the response and the direction of incidence may be quite complicated, the response being zero in several directions. As a function of wave frequency, the response may also have several zero values within the frequency band in which reflections are expectable. This would result in a serious modification of the filter characteristics of the amplifier. It is shown, however, how such a modification of the filter characteristics may be avoided by a judicious choice of the number and the spacing of the geophones in a multiple group.
-
-
-
BOOK REVIEW
Available online: 09 October 2008More LessBook review in this article
L. W. Sorokin. – Lehrbuch der Geophysikalischen Methoden zur Erkundung von Erdölvorkommen.
M. R. J. Wyllie. – The fundamentals of electric log interpretation. Academic Press Inc. – New York, Sept. 1954. Price $ 3.60.
-
-
-
-
-
TIDAL GRAVITY CORRECTIONS FOR 1962 by Service Hydrographique de la Marine and Compagnie Générale de Géophysique
By Jean GoguelAvailable online: 27 April 2006More Less
-
-
-
-
-
-
-
-
-
-
-
EARTH TILTS AND THE FLOW OF OIL WELLS*
Available online: 27 April 2006More LessAbstractIt has been discovered that certain flowing oilwells in the Eakring area (Nottinghamshire, England), which have not otherwise been disturbed, show distinct annual variations in the flow of total fluid. There appears to be a definite connection between these variations and the seasonal movements of the earth's crustal layers as evidenced by observations of the tilts of the earth's surface. The investigation has been extended further to show that a similar relation exists between the earth tilts and the production of a whole oilfield which has not been disturbed unduly by outside influences.
A correlation has also been established between the earth tilt observations and the periodicity of shallow earthquakes.
-
-
-
SOME EXAMPLES OF THE APPLICATION OF ISOSTASY*
Available online: 27 April 2006More LessAbstractIt is pointed out that the isostatic correction of regional Bouguer isogam maps is necessary for their interpretation. The work involved in the computation of the necessary isostatic reductions is greatly reduced when isostatic iso‐correction line maps are made.
-