Water resources data for Alachua, Bradford, Clay, and Union Counties, Florida

A study of the water resources of Alachua, Bradford, Clay, and Union counties, Florida (fig. 1), was made by the Water Resources Division of the U. S. Geological Survey in cooperation with the Florida Geological Survey during the period 1957-61. The results of this study will be published by the Florida Geological Survey in the following reports by William E. Clark, Rufus H. Musgrove, Clarence G. Menke, and Joseph W. Cagle, Jr.: "Interim Report on the Water Resources of Alachua, Bradford, Clay, and Union Counties, Florida," "Water Resources of Alachua, Bradford, Clay, and Union Counties, Florida," and "Hydrology of Brooklyn Lake, near Keystone Heights, Florida." (Document has 161 pages.

Constraints upon water advection in sediments of the Mariana Trough

Thermal gradient measurements, consolidation tests, and pore water compositions from the Mariana Trough imply that water is moving through the sediments in areas with less than about 100 m of sediment cover. The maximum advection rates implied by the thermal measurements and consolidation tests may be as high as 10−5 cm s−1 but are most commonly in the range of 1 to 5×10−6 cm s−1. Theoretical calculations of the effect of the highest advection rates upon carbonate dissolution indicate that dissolution may be impeded or enhanced (depending upon the direction of flow) by a factor of 2 to 5 times the rate for diffusion alone. The average percentage of carbonate is consistently higher in two cores from the area with no advection or upward advection than the average percentage of carbonate in three cores from the area with downward advection. This increase in average amount of carbonate in cores with upward moving water or no movement cannot be attributed solely to differences in water depth or in amount of terrigenous dilution. If the sediment column acts as a passive boundary layer, then the water velocities necessary to affect chemical gradients of silica are in the range 10−9 to 10−10 cm s−l. However, if dissolution of silica occurs within the sediment column, then the advection velocities needed to affect chemical gradients are at least 3×10−8 cm s−l and may be as high as 3×10−6 cm s−l. This order of magnitude increase in advection velocities when chemical reactions occur within the sediments is probably applicable to other cations in addition to silica. If so, then the advection velocities needed to affect heat flow ( >10−8 cm s−1) and pore water chemical gradients are much nearer in magnitude than previously assumed

Determining the orientations of ocean bottom seismometers using ambient noise correlation

The cross-correlation of multicomponent ambient seismic noise can reveal both the velocity and polarization of surface waves propagating between pairs of stations. We explore this property to develop a novel method for determining the horizontal orientation of ocean bottom seismometers (OBS) by analyzing the polarization of Rayleigh waves retrieved from ambient noise cross-correlation. We demonstrate that the sensor orientations can be estimated through maximizing the correlation between the radial-vertical component and the phase-shifted vertical-vertical component of the empirical Green's tensor. We apply this new method to the ELSC (Eastern Lau Spreading Center) OBS experiment data set and illustrate its robustness by comparing the obtained orientations with results from a conventional method utilizing teleseismic P and Rayleigh wave polarizations. When applied to a large OBS array, the ambient noise method provides a larger number of orientation estimates and better azimuthal coverage than typically is possible with traditional methods

Nonlinear adaptive control using backpropagating neural networks

The objective of this research is to develop a nonlinear regulator for an adaptive control system using backpropagating neural networks (BNN's) in conjunction with a linear quadratic regulator (LQR). the basic concepts of adaptive control and the structure of neural networks are discussed. These concepts are integrated and the nonlinear regulator is derived. Simulation is conducted on a representative nonlinear system with both the LQR and the nonlinear regulator. Training of the regulator and its performance under varying BNN parameter values are examined. The simulation results show that the nonlinear regulator with BNN's exhibits superior performance compared to the LQR when the nonlinearities are large. The optimization of regulator performance with regard to BNN parameter values is discussed. Further research is required in order to determine the general applicability of this regulator and to develop more specific guidelines for BNN parameters.http://archive.org/details/nonlinearadaptiv00menkLieutenant, United States NavyApproved for public release; distribution is unlimited

Lateral variation of P velocity in the Himalayan crust and upper mantle : a study based on observations of teleseisms at the Tarbela seismic array.

Thesis. 1976. M.S. cn--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences.Microfiche copy available in Archives and Science.Bibliography: leaf 72.M.S.c

Reinterpretation of the RRISP-77 Iceland shear-wave profiles

Two shear-wave profiles, E and G, collected during the 1977 Reykjanes Ridge Iceland Seismic Experiment have played an important role in models of the Icelandic crust. They were originally interpreted as indicating very low shear-wave velocities and abnormally low shear-wave quality factors in the 10–15 km depth range. These attributes, which are indicative of near-solidus temperatures, were used to support the hypothesis that the crust of Iceland is relatively thin (10–15 km) and underlain by partially molten material. More recent seismic data, however, contradict this hypothesis and suggest that the crust is thicker (20–30 km) and cooler. A re-examination of the RRISP-77 data indicates that the low shear-wave velocities are artefacts arising from source static anomalies (in the case of profile G) and misidentification of a secondary shear phase, SmS, as S (in the case of profile E). Furthermore, the attenuation occurs at ranges when rays from the shots pass near the Askja (profile E) and Katla and Oraefajokull (profile G) volcanoes. It may therefore have a localized source, and not be diagnostic of Icelandic crust as a whole. This new interpretation of the RRISP-77 shear-wave data is consistent with models having a thick, cold crust.We thank 0. Flovenz, one of the principal investigators of the SIST experiment, G. Foulger and B. Julian, principal investigators of the Hengill experiment, and the Incorporated Research Institutions for Seismology for providing us with copies of the data. Lamont Doherty Contribution Number 5513Peer Reviewe

Evidence for excess pore pressures in southwest Indian Ocean sediments

Brown clay cores from the Madagascar and Crozet basins show the following evidence of excess pore pressures: large amounts of flow-in, increasing average sedimentation rate with age, and nonlinear temperature gradients. Additionally, many hilltops in these basins have no visible sediment cover. The bare hilltops may result from periodic slumping caused by excess pore pressures. Calculated excess pore pressures which equal or exceed the overburden pressure were inferred from water fluxes predicted by nonlinear temperature gradients and laboratory permeability measurements by using Darcy's law. Since pore pressures which exceed the overburden pressure are unreasonable, we attribute this discrepancy to laboratory measurements which underestimate the in situ permeability. The widespread presence of overpressured sediments in areas of irregular topography provides a process for resuspension of clay-sized particles. This mechanism does not require high current velocities for the erosion of clay and therefore can be applied to many areas where no strong currents are evident. Carbonate-rich sediments from the Madagascar Ridge, the Mozambique Ridge, and the Agulhas Plateau had almost no flow-in and occurred in areas where all topography was thickly draped with sediment. Since the age and tectonic location of the ridges and plateaus preclude water circulation in the basement, we attribute these differences between the brown clay and the carbonate-rich material to an absence of significant excess pore pressures in the plateau and ridge sediments

Application of the POCS inversion method to cross‐borehole imaging

Publisher's version (útgefin grein)Cross-borehole tomography suffers from a well-known problem of data incompleteness: the limited ray coverage dictated by the poor experimental geometry implies that certain features of the velocity field are not determined by the data. Construction of a tomographic image of the velocity field therefore requires the addition of prior constraints to the inversion. In the Fourier wavenumber domain (assuming straight-line rays), the process of adding prior constraints is equivalent to specifying unmeasured wavenumber coefficients. The projection onto convex sets (POCS) algorithm can impose physically plausible constraints that allow high quality tomographic images to be produced. Each constraint is viewed as defining a set (in function space) of images that satisfy that particular constraint. The POCS method finds one or more images in the intersection of the constraining sets, which is equivalent to finding an image that simultaneously satisfies a number of constraints including the observed data. The sets of images that we employ include: those that satisfy the data in the sense of having certain known wavenumber components, those that have bounded energy in certain unmeasured wavenumber components, those that have seismic velocity bounded everywhere (e.g., nonnegative), and those in which the velocity structure is confined to the region between the boreholes. An advantage of the POCS algorithm is that it allows both space-domain and wavenumber-domain constraints to be imposed simultaneously. In our implementation of the POCS algorithm, we make use of the fast Fourier transform to rapidly iterate between the space and Fourier-wavenumber domains. We test the method on synthetic data, and show that it significantly reduces the artifacts in the image, when compared to other methods. We then apply it to data from a cross-borehole experiment in Manitoba, Canada, that were previously studied by others. We achieve a tomographic image of the velocity field that is similar in many respects to the results of others, but which possesses fewer artifacts.This work was supported by the National Science Foundation and the Office for Naval Research. This is Lamont- Doherty contribution number 5042.Peer Reviewe

Correlated sediment thickness, temperature gradient and excess pore pressure in a marine fault block basin

Measurements of temperature gradient and excess pore pressure in the surficial sediment of a fault block basin in the Guatemala Basin correlate with sediment thickness. The temperature gradient is smaller and the excess pore pressure gradient is more negative in areas of thinner sediment. This correlation is explained by postulating downward pore water advection within the sediments, with flow velocities on the order of 10−9 to 10−8 m/s in the thinnest sediments and much less flow in the thickest sediments. Sediment physical properties and pore water chemistry also support this interpretation. Since the conductive heat flow of the basin as a whole is less than one third that predicted by sea floor spreading models, the oceanic basement may be the site of a vigorous hydrothermal circulation system. The pore water advection in the sediments may be driven by this larger scale circulation