Mark R. Baker

Geophysical and geochronological constraints on the extent and age of mafic intrusions in the basement of west Texas and eastern New Mexico

A deep drill hole recently completed on the Central basin platform of west Texas provides a rare look at almost 5 km of basement rocks. Most of the crystalline rocks encountered were basic and ultrabasic in composition. A variety of geophysical data is available from the bore hole and vicinity. The petrographic and geophysical data suggest that a large, layered, basic intrusion was penetrated by the well. Geochronologic (U-Pb) data indicate an age of about 1.1 Ga for this intrusion. This date has significant tectonic implications because it indicates that commonly accepted analogies with the southern Oklahoma aulacogen (550 Ma rifting) are not valid. However, it is interesting to note that this feature formed during another widespread period of rifting (Keweenawan).

Estimating Uncertainties for Geophysical Tomography

We present statistical and interval techniques for evaluating the uncertainties associated with geophysical tomographic inversion problems, including estimation of data errors, model errors, and total solution uncertainties. These techniques are applied to the inversion of traveltime data collected in a cross well seismic experiment. The inversion method uses the conjugate gradient technique, incorporating expert knowledge of data and model uncertainty to stabilize the solution. The technique produced smaller uncertainty than previous tomographic inversion of the data.

Assessing Quality of Concrete with Wave Propagation Techniques

An instrument for monitoring the quality and thickness of slabs has been designed. The quality is assessed by estimating the slabs Youngs and shear moduli from ultrasonic surface wave and ultrasonic body wave velocities. The thickness is determined from results obtained with the impact echo and above tests. In this paper, the conceptual and actual designs of the device are described, the advantages of, and problems with the approaches reported, the theoretical limitations of the methodologies expanded, and the results from several field-testing programs discussed. Based on test results, the device is quite promising, and its capabilities are more diverse than those of existing devices.

Distribution and Generation of the Overpressure System, Eastern Delaware Basin, Western Texas and Southern New Mexico

Three subsurface pressure systems have been identified in the Delaware basin: an upper normal pressure system, a middle overpressure system, and a lower normal pressure system. The overpressure system occurs in the eastern Delaware basin, covering six Texas and New Mexico counties. The depth of the overpressure system ranges from 3100 to 5400 m. The normal fluid pressure gradient is 0.0103 MPa/m in the eastern Delaware basin. The highest overpressure gradient, however, approaches 0.02 MPa/m, which is close to the lithostatic gradient of 0.0231 MPa/m. The overpressure system has a relatively flat top and a downwarped bottom. The maximum thickness of the overpressure system reaches about 2300 m at the depocenter and pinches out toward the edges. An area of excess pressure o curs within the system where the highest excess pressure reaches 60 MPa. Local underpressured areas due to production are found in the lower normal pressure system in the War-Wink field area. Overpressure in the eastern Delaware basin is mainly associated with Mississippian, Pennsylvanian, and Permian (Wolfcampian) shale sequences, which also are major source rocks in the basin. Initial sedimentation rates within the overpressure system range from 17 to 90 m/m.y. Corrected bottom-hole temperature measurements indicate that the geothermal gradient within the overpressure zone is 25.1°C/km, which is higher than the basins average geothermal gradient of 21°C/km. Temperatures at the top and bottom of the overpressure system are about 80 and 115°C, respectively. This temperature range approximates the temperature of the average clay dehydration zone. The oil window in the War-Wink field is coincident with the overpressure system, which implies that hydrocarbon g neration and migration are active in the overpressure system. A two-stage overpressure model is proposed. Hydrocarbon maturation combined with mechanical compaction disequilibrium and clay dehydration are the initial causes for overpressure generation due to an abnormal increase of fluid volume and pore space. Subsequently, the increase in temperature due to a decrease of thermal conductivity and fluid migration within the preexisting overpressure system would reinforce further overpressuring due to the fluid thermal expansion.

Universal Approximation Theorem for Interval Neural Networks

One of the main computer-learning tools is an (artificial) neural network (NN); based on the values y(p) of a certain physical quantity y at several points x(p)=(x1(p) ,...,xn(p)), the NN finds a dependence y = f(x1,...,xn) that explains all known observations and predicts the value of y for other x = (x1,...,xn). The ability to describe an arbitrary dependence follows from the universal approximation theorem, according to which an arbitrary continuous function of a bounded set can be, within a given accuracy, approximated by an appropriate NN.The measured values of y are often only known with interval uncertainty. To describe such situations, we can allow interval parameters in a NN and thus, consider an interval NN. In this paper, we prove the universal approximation theorem for such interval NNs.

Monitoring Yearly Changes and Their Influence on Electrical Properties of the Shallow Subsurface at Two Sites Near the Rio Grande, West Texas

We present the results of a case study that monitored changes in the electrical properties of soils on a bi-monthly basis between August 1999 and November 2000 at two sites located along the banks of the Rio Grande, west Texas. One site was located within an abandoned channel of the Rio Grande and showed relatively homogeneous layering, while the second site exhibited complex interfingerings of crevasse splay (sands and silts) and floodplain muds. Repeated EM-31 ground conductivity measurements at both sites showed that conductivities within the upper 3m of soil could change by up to a factor of 2 within a year’s time. DC resistivity studies suggested up to a factor of 5 change in resistivity values within the upper 1m of soil. These changes appear to be related to remobilization of salt in the soil following rainfall or irrigation events. These dramatic fluctuations make it difficult to image deeper (>5m depth) conductivity changes in the subsurface.

Costs of Urban Congestion in Canada : A Model-Based Approach

The ability to address congestion requires, first, an understanding of the topic. To this end, different methods have been developed to quantify and compare congestion. A recent research study developed methods to quantify congestion and its costs in the nine largest urban areas in Canada. Three components of congestion and its costs—delay, wasted fuel, and greenhouse gas emissions—were developed. The methods were based on the travel demand—forecasting models of each urban area. In contrast to well-known methods such as the annual Urban Mobility Report in the United States, which uses common sets of data to allow a comparison of congestion in 85 urban areas, a comparative analysis was not possible because the models differ in structure, definition, and base data. Conversely, the model-based approach supports significantly more analytical depth, allows planners in individual urban areas to customize the tools, and provides a means to account for congestion in forecasts and in the development and evaluation of long-range transportation plans. It also provides a basis for linking the engineering aspects of congestion with the broader economic perspectives. The approach used in the Canadian study has potential for metropolitan planning organizations, state departments of transportation, and other U.S. transportation planning authorities that seek to incorporate the analysis of congestion into their long-range transportation planning, programming, and budgeting processes.

Seasonal Variations in Geophysical Surveys of Alluvial Sediments Near the Rio Grande, West Texas

We have used geophysical techniques (seismic refraction, DC resistivity, conductivity, spectral analysis of surface waves) to examine the ability of these surveys to determine grain size/stratigraphy variations in alluvial sediments along a two-dimensional profile near the Rio Grande in west Texas. We also examined the variation in survey results through time and found that there were large temporal variations in the geophysical properties of the sediments due to changes in water table depth, soil salinity, and moisture content. Geological information from boreholes has helped us to separate these seasonal effects from stratigraphic and grain size variations. Our goal was to determine which geophysical techniques would work best for determining geologic variations, regardless of the season of the investigation. Our results show that temporal changes in soil moisture and soil salinity caused up to 25% variations in shear/compressional velocities of seismic waves and up to 50% variations in conductivity/resistivity values. It was difficult to compare measurements from different geophysical surveys unless they were conducted at nearly the same time. A combination of resistivity with the spectral analysis of surface waves technique appears to be the fastest, most reliable, joint technique to determine geological, soil moisture and salinity variations.

Practical Estimation of Near-surface Bulk Density Variations Across the Border Ranges Fault System, Central Kenai Peninsula, Alaska

ABSTRACT We demonstrate a near-surface density estimation approach in an area without exposed outcrop or where outcrop occurrences do not adequately represent the subsurface rock densities based on the Nettleton (1939)-Parasnis (1952) technique as extended by Rao and Murty (1973). We applied this technique in the central Kenai Peninsula, Alaska where the region is cut by a major fault zone, the Border Ranges fault system, that juxtaposes two terranes with greatly varying geological and geophysical properties. The Kenai Peninsula region can be generally divided into two different geologic settings: recent fluvial and glacial deposits of the Cook Inlet basin to the west and accreted metamorphic terranes of the Kenai Mountains to the east. Our study region includes glacial cover, deep lakes, and large topographically-driven gravity gradients between the Kenai Mountains and Cook Inlet. We selected 11 gravity loops from ∼580 gravity points collected in 2009, which have 10–20 gravity points per loop; nine loops...

User-friendly surface wave method for integrity evaluation

The use of the spectral-analysis-of-surface wave (SASW) method is becoming more common as a tool for integrity testing of lifeline and infrastructure components. The method, which is based upon a fundamentally correct theoretical background, can be utilized at several scales. So far, the method has been used in numerous projects dealing with diverse topics from the integrity of dam foundations, to the soundness of concrete slabs, to the suitability of structural members. In this paper, the efforts by the authors towards developing automated procedures at three different scales are described. First, an automated procedure for reducing data for large scale tests (depth of penetration up to 100 m) is presented. In the second section, a new trailer- mounted device, that in less than 40 sec automatically collects and interprets SASW data, is described. Finally, a new hand-held device, that in less than fifteen seconds, collects, reduces, and archives the results over a distance of 15 cm, is presented.