Browsing by Author "De Bremaecker, Jean-Claude"
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Item Anomalies in P wave velocities in the Tampico embayment, Gulf Coast of Mexico(1967) Camargo Zanoguera, Antonio; De Bremaecker, Jean-ClaudeThe objective of this study was to discover relationships between seismic velocities and stratigraphic and tectonic zones of possible oil accumulation, by extrapolating velocity relations from known geologic features and oil fields in the Tampico Region. The original velocity data from the Tampico Region, consisting of vertical time-depth relations for longitudinal waves, was obtained by shooting wells and long reflection profiles for velocities. This data was converted to velocity functions that could be used in the computation of velocity maps for single formations, groups of formations, and 250 meters thick depth-intervals. The velocity functions were computed by fitting polynomials by Least Squares methods to the vertical time-depth data. The analysis of the velocity data was done by computing the regional trend of the velocity maps in each case, and then computing the residuals, which show the relationships between velocities and geologic features. The regional was computed according to the concept of a smooth regional. Thus a low order polynomial in x and y - a surface - was fitted by Least Squares method to the non-anomalous irregularly distributed data to represent the regional. The fitting of the velocity functions and of the surfaces, and the graphing and mapping was done using the IBM-7040 computer of the Rice Computer Center. Regional maps computed on formation datum show the general trend of variations of velocities. Velocities augment toward the Sierra Madre Oriental. The residual maps show good correlation with the tectonics of the area. The results are difficult to interpret as functions of known geologic features on the 250-meter depth-interval maps. The regional maps show the same tendency for the velocity to increase toward the Sierra. However, the residual maps do not show features consistently ascribable to the known geologic features, and it is difficult to hypothesize about the features present on the maps without additional information. No conclusion has been made regarding better prospective zones for oil accumulation; this is due mainly to the insufficiency of the velocity data. A density of about one velocity determination for each 20 square kilometers or less is desirable. Nevertheless, it has been proved that definite relations exist between velocities and structures in the Tampico Region.Item Automatic detection of seismic reflections(1969) Aspiroz Aguilar, Rogelio; De Bremaecker, Jean-ClaudeThe purpose of this study is the automatic detection of reflections in seismograms used in oil exploration by examining the statistical moments in successive time windows. Two of the information-bearing features of a reflection are examined : frequency of the zero-crossings and the amplitude. The standard deviation of the amplitudes of a sharply filtered trace appears to be a reliable criterion. However, if the trace is not sharply filtered, the method fails. The distribution of the frequency of zero-crossings does not appear to be a reliable criterion.Item Azimuthal variation in Pn velocity around the GNOME explosion(1963) Wu, Chang Sheng; De Bremaecker, Jean-ClaudeThe stations which recorded the GNOME explosion in the continental United States can be arranged into 8 more or less linear profiles centered on ground zero. The P wave velocities in an area within 300 km of the explosion yield the following results: 5.55 km of layer 1 --- velocity 4.86 km/sec, 17.85 km of layer 2 --- velocity 6.20 km/sec, 20.84 km of layer 3 --- velocity 6.64 km/sec, the velocity of the underlying material is 7.81 km/sec. The velocities of Pn along the profiles are : 8. 37--8. 43-- 8.49-7.99-7.86-7.82--8.00 and 8.12 km/sec as the azimuth of the profiles changes counterclockwise beginning from the east. These observations strongly suggest regional variations in the mantle material. P velocities show the same trend as the Pn velocities. Travel times at stations west of Sierra Nevada show delays caused by mountain roots.Item Finite element modeling of thrust faulting(1992) Vague, Glen Edward, Jr; De Bremaecker, Jean-ClaudeFinite Element modeling of thrust faulting shows that the faults will propagate upward at very low angles from the leading edge of a regional horizontal decollement surface located at various depths in a homogeneous block of crustal material. The angles are consistent with Mode II crack propagation in Linear Elastic Fracture Mechanics and the relationship of stress trajectory and failure in the classic theory of shear fracture. Shallow faults will propagate at a steeper angle than deeper ones. The coefficient of friction does not affect the fault angle, though it probably affects the likelihood of Mode II deformation.Item Geology of Culebra Island, Puerto Rico(1962) Banks, Thomas H; De Bremaecker, Jean-ClaudeCulebra Island, located about twenty miles east of Puerto Rico, is composed of undated andesite and spilitic volcanics which are intruded by diorite plutons. On the basis of the ages of similar rocks on Puerto Rico and the Virgin Islands the age of the Culebran rocks is probably within the Albian - Middle Eocene interval. The oldest rocks in the area are the Culebra Andesites (2400 feet exposed) which consist of augite andesite pillow lavas and massive flows interbedded with coarse andesite breccia and andesite tuff. Conformably overlying the Culebra Andesites is the Cerro Balcon Formation (1300 feet exposed). This formation is composed of thick-bedded spilitic lapilli tuff with a basal unit of thin-bedded, fine grained tuff called the Playa Resaca Member. The Cayo Norte Formation (750 feet exposed) is composed of albitic, quartz-rich pillow lavas which are the youngest stratified rocks in the area. Intrusive igneous rocks include two diorite stocks, a diorite dike and several small spilite intrusives. The rocks of Culebra are unmetamorphosed except for contact metamorphism of tuffs adjacent to the diorite intrusives. Structurally, Culebra is a homocline dipping 15° to the northeast. At least three northwest trending high angle faults cut the area. Stratigraphic throws are from a few hundred to about a thousand feet. The Culebra Andesites are considered to be orogenic igneous rocks which are related to the high-alumina basalt described by Kuno (1960). Orogenic andesites may be derived from high-alumina basalt by fractional crystallization or may simply represent a slightly lower melting fraction of the ultramafic material of the mantle. High-alumina basalts and related andesites are considered to be primary magmas which are generated by partial melting of the ultramafic mantle in active orogenic areas.Item Investigation of the common depth point method by means of synthetic seismograms(1968) Ponce de Leon Garnica, Jose; De Bremaecker, Jean-ClaudeIn seismic reflection shooting, some of the traces correspond to relatively large angles of incidence, especially when the method of common depth point is used. In an effort to observe the effect of the angles of incidence on traces with common depth point, approximations of synthetic seismograms at oblique incidence with and without multiples were constructed. The theory of constructing a synthetic seismogram is briefly explained, under the assumption that S waves do not exist. After obtaining three approximations of synthetic seismograms for assumed shot point to geophone distances of 400, 800, and 1200 feet respectively, the effects of initial suppression, filter, and automatic gain control were simulated. The three synthetic seismograms so obtained were staked together to obtain a single seismogram for various comparisons. It is concluded that as the angles of incidence of the shot traces increase, so do the differences with respect to a trace shot at normal incidence. From the comparison of the stacked traces it is proved that the common depth point stacking process leads to a better definition of the character of the reflections, in comparison with the conventional process.Item Nonlinear effects near an explosions(1969) Alvarado de la Tejera, Salvador; De Bremaecker, Jean-ClaudeThe purpose of this study is to find the dimensions of the shattered zone produced by the explosion of a spherical charge, in terms of the properties of the medium and the weight of the explosive charge; and then, to establish a relationship between the size of this nonlinear region and the frequency spectrum of the elastic signal. The computation of the size of the shattered zone, shows that this region is bounded by a so called "Critical Radius," which occurs when the shock wave pressure caused by the explosion decreases in value until it equals the yield strength of the medium. Within this region, different values of the shock wave pressure for different values of explosive charges follow the Principle of Similarity. The calculation of the frequency spectra, shows that for an ideally elastic medium, the shape of the frequency spectrum of the signal outside the shattered zone, changes as a function of both the critical radius and the P-wave velocity of the medium.Item Study of multiple reflections with the use of synthetic seismogram(1968) Palafox, Hector; De Bremaecker, Jean-ClaudeUsing a velocity log from a given area impulsional synthetic seismograms with and without multiples are computed by digital techniques. The effect of the automatic gain control and of the recording process are then taken into account by using the digital filters corresponding to the actual analog systems. The resulting synthetic seismograms are compared, the multiples are identified and their probable origins are found. Further comparison with the actual field record obtained in the area shows an excellent agreement with the synthetic seismogram with multiples.Item Study of the action of filters on a given signal(1969) Hernandez Gonzalez, Salvador; De Bremaecker, Jean-ClaudeA method has been developed by which a deconvolution filter is designed and applied to a "seismogram" whose initial signal is unknown. Considering a known signal composed of spikes of random amplitude and distributed at random times a "seismogram" can be simulated from which the inverse of its amplitude spectrum is obtained. This inverse is considered to be the amplitude-response of the desired filter. From the results of two examples it has been concluded that the information contained in the "seismograms" may be improved by using this method.Item The direction of fracture initiation(1992) Wei, Kaihong; De Bremaecker, Jean-ClaudeThe preferential orientation for the initiation or extension of a crack is the one which gives the maximum strain energy reduction for a given crack length. This criterion is based on the concept of maximum energy release rate, and makes no assumptions on the configuration, the homogeneity, the stress condition on the crack faces, or the material response. Consequently it is valid under the usual engineering conditions as well as under compression and high confining pressures such as obtain inside the Earth; in the latter case it replaces the empirical and approximate Coulomb-Mohr criterion. The mathematical formulation of the criterion is approached by way of constrained optimization, and the solution is proven to exist uniquely. The numerical implementation is based on a finite element scheme. An iterative method is employed to handle the material and geometric non-linearity. Test cases agree with laboratory and field data.Item The growth of fractures in the Earth(1994) Wei, Kaihong; De Bremaecker, Jean-ClaudeFracture growth under compressive loading is studied using the maximum strain energy release rate criterion by means of both the finite element and the boundary element methods. Although this approach is computationally intensive, it is indispensable for this type of problem because other criteria cannot account for the friction effect on the fracture faces. We use a repulsion scheme to handle the frictional contact constraints on the fracture faces: the interpenetration is eliminated by adjusting the normal compressive force (repulsion), and the friction law is satisfied by modifying the friction resistance at each iteration. Our results explain the fact that a natural fracture under uniaxial compression often grows in its own plane, while an artificial cut grows by means of a kink: the reason lies in the lower friction coefficient on an artificial cut than on a natural fracture. Fracture growth under simple shear and under transtension occurs by a kink and along a smooth, slightly convex trajectory; the computed path is almost identical to the one obtained in the laboratory. Under transpression, fracture also grows by a kink and along a smooth trajectory which is of the opposite convexity than in the previous case, when compression is large. Right-stepping fractures under a left-lateral shearing run away from each other when their centers are more than one fracture length distant; when this is not the case, they turn toward each other. Interaction is thus significant only in this last case. Geologically, our results imply that essentially planar faults may be due to continuing remote compressional stress at about 30$\sp\circ$ to the fault, while abrupt changes in orientation may indicate that the previous stress has been replaced by a remote shear stress. Finally, a convex fault path may indicate simple shear or transtension, whereas a concave one may indicate transpression.