Geophysical study of the structure and processes of the continental convergence zones: Alpine-Himalayan belt

Studies of the structure of the continental collision zones using seismic and body waves, theoretical modelling of the thermal regime of the convergence processes, and studies of earthquake mechanisms and deformation aspects of the model are covered

MPLS Automatic Bandwidth Allocation via Adaptive Hysteresis

Cataloged from PDF version of article.MPLS automatic bandwidth allocation (or provisioning) refers to the process of dynamically updating the bandwidth allocation of a label switched path on the basis of actual aggregate traffic demand on this path. Since bandwidth updates require signaling, it is common to limit the rate of updates to reduce signaling costs. In this article, we propose a model-free asynchronous adaptive hysteresis algorithm for MPLS automatic bandwidth allocation under bandwidth update rate constraints. We validate the effectiveness of the proposed approach by comparing it against existing schemes in (i) voice and (ii) data traffic scenarios. The proposed method can also be used in more general GMPLS networks. (C) 2010 Elsevier B.V. All rights reserved

Electrokinetics Of A Fluid-Saturated Rock Sample: Laboratory Experiments

The conversion between seismic and electromagnetic energies was discovered in a fluidfilled porous formation. When seismic waves propagate through a fluid-saturated porous formation, relative motion between the pore fluid and the solid matrix is generated and cation motion in the fluid is formed. The streaming electric current induces electromagnetic waves in the formation. There is an opposite phenomenon, i.e., the conversion of electric energy into acoustic energy in the porous formation. The electroseismics in porous sandstone samples are investigated by ultrasonic experiments in our laboratory. A compressional or a shear transducer excites an acoustic wave in the water-saturated sample and the electric signals generated on the surface are measured by an electrode. The relationship between the electric potential and acoustic wave or the conductivity of water-saturated rocks is studied. The electro-seismic conversion in rock samples is also investigated. Electroseismics could provide an effective means for estimating the fluid-saturated porous formation.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumUnited States. Dept. of Energy (Grant DE-FG02-93ERI4322

Ultrasonic Laboratory Study of Full Waveform Acoustic Logs in Boreholes with Fractures

A set of ultrasonic experiments was carried out to determine the effects of horizontal and vertical fractures on full waveform acoustic logs. Boreholes of 1 cm diameter were drilled in aluminum blocks. Measurements were made with horizontal fractures of 0.05 mm, 1.0 mm, 2.5 mm, and 4.5 mm width and a vertical fracture of 1.0 mm width. The horizontal fractures of even the smallest thickness significantly attenuate the P, S, and pseudo-Rayleigh waves. The Stoneley waves are the least attenuated, and attenuation increases with increasing fracture width. The vertical fracture attenuates Stoneley waves most significantly. Both scattering and fluid flow playa role in attenuation. The results may qualitatively be extended to inclined open fractures, where we expect strong attenuation of P and S waves and moderate attenuation of Stoneley waves.Massachusetts Institute of Technology. Full Waveform Acoustic Logging Consortiu

Velocity Anisotropy Of Two Deep Crystalline Samples

Using ultrasonic velocity measurements taken over a multiplicity of directions we show that samples exhibit weak to moderate anisotropy of seismic velocities. We further define the anisotropic geometry with high resolution scanning electron microscopy. Our data indicate that one sample, a granite, is transversely anisotropic, and that the presence of fine to moderately fine microcracks is the most important factor effecting the velocities. We model the angular velocity dependence using 5 elastic constants and show that all 9 observed velocities fit these predictions to within 0.1 km/s. We are unable to obtain similar fits to a second sample, a mica-schist, in the same fashion. SEM observations indicate this rock displays orthorhombic symmetry. We made additional velocity measurements in order to calculate 9 elastic constants, and found that the predicted angular velocity dependence agreed much better with our velocity observations.Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumEnte nazionale per l'energia elettric

Full Waveform Acoustic Logging - From Theory To Applications

This report contains results from the third year of the Full Waveform Acoustic Logging Consortium and rock physics studies at M.J.T. This year marks the completion of the first phase of the project which has been directed primarily to the understanding of the basic theoretical aspects of acoustic waves in a borehole. With such a background we are ready to emphasize applications as well as to undertake special problems which require new and different theoretical approaches. As examples of the latter, we can mention uncentered tools, vertical fractures around boreholes, thinly bedded formations and anisotropy. The third year studies fall into four general areas: theoretical aspects of wave propagation in the borehole, applications to the characterization of formations, integrated log analysis and physical properties of sedimentary rocks relevant to logging. There are fifteen papers in this report which discuss individual topics in detail. In this introduction we summarize the major points and also list the potential applications of full waveform acoustic logs and future directions of our research

Modeling Of Seismoelectric Effects In A Borehole

We present a method to simulate the propagation of seismic and converted electromagnetic waves generated by a mechanical borehole source embedded in a layered poroelastic medium. The electroseismic conversions occur at both the borehole wall and the layer boundaries. Most studies in electroseismic effects have been modelled and tested with seismic sources and detectors (geophones and antennas) at the surface. In this paper, we investigate the case of a seismic source in a borehole and receivers either at the surface or embedded in the medium. The method is formulated as a boundary element technique (where the poroelastic displacement and relative flow Green's functions are calculated by the discrete wavenumber method. The singular properties of the Green's functions are determined analytically using static Green's functions to regularize the integrals. This is necessary to calculate the element's self interaction. The borehole is cylindrical and its axis rulls normal to the interfaces. The coupled electroseismic effects in the layered media are included by using the global matrix technique. The developed method is an extension of the model of Biot-Rosenbaum, who applied the wavenumber integration technique to investigate the effect of formation permeability on Stoneley waves, using Biot's theory to model the wave propagation effects of a homogeneous permeable formation surrounding a borehole. We extend the Biot-Rosenbaum model by including the effect of a heterogeneous permeable formation surrounding the borehole. The effect of formation permeable zones (or fractured zones) on Stoneley waves can now be investigated. The other modification is the inclusion of conversions of mechanical into electromagnetic waves at mechanical and/or electrical contrasts in the poroelastic formation. The converted electromagnetic fields are sensitive to large permeability contrasts and fluid chemistry contrasts inside a reservoir. Using the electroseismic method downhole will provide more information about permeability/permeability contrasts in the formation, as well as additional lithological information (salinity of the fluids)

Electroseismic Waves From Point Sources In Layered Media

The macroscopic governing equations controlling the coupled electromagnetics and acoustics of porous media are numerically solved for the case of a layered poro-elastic medium.It is shown that these coupled equations decouple into two equation sets describing two uncoupled wavefield pictures. That is, the PSVTM picture where the compressional and vertical polarized mechanical waves drive currents in the PSV particle motion plane that couples to the electromagnetic wavefield components of the TM mode. And the SHTE picture where the horizontal polarized rotational mechanical waves drive currents in the SH particle motion plane that couples to the electromagnetic wavefield components of the T E mode. The global matrix method is employed in computing electroseismograms in layered poro-elastic media in the PSVTM picture. The principal features of the converted electromagnetic signals are the following: (1) contacts all antennas at approximately the same time; (2) arrives at the antennas at half of the seismic traveltime at normal incidence reflected P waves; and (3) changes sign on opposite sides of the shot. The seismic pulse is shown to induce electric fields that travel with the compressional wavespeed and magnetic fields that travel with the rotational wavefield. The frequency content of the converted electromagnetic field has the same frequency content of the driving incident seismic pulse, as long as the propagation distances are much less than the electromagnetic skin depth. Snapshots in time and converted electromagnetic amplitudes versus seismic point source-antenna offset-are calculated for contrasts in mechanical and/or electrical medium property. Conversion happens there where the seismic wavefront passes a contrast in medium properties due to generated imbalances in current across the contrast. The TM component amplitude radiation pattern away from the interface shows similarities with an effective electric dipole radiation pattern, or its dual, an effective magnetic current loop radiation pattern centered right beneath the source at the contrast's depth. The TM mode amplitudes decay rapidly with traveled distance and suggest the importance of a Vertical Electroseismic Profiling geometry to enhance recording of the converted electromagnetic signal by positioning the antennas closer to the target (contrast) of interest.United States. Dept. of Energy. Office of Energy Research (Grant DE-FG02-93ERI4322

Dispersive Wave Analysis – Method and Applications

A technique for estimating the dispersion characteristics of propagating waves as measured by an array is detailed. The technique consists of bandpass filtering the data through a filterbank and then processing the filtered waveforms non-dispersively. The results can show the dispersion of the entire time series or be parsed in time to analyze the dispersion characteristics of any section of the time series. Processing LWD field data shows that this method can extract dispersion characteristics over a broadband of frequencies and with low amplitude signals. Both the field data and laboratory scale data show that multiple modes present over the same frequency band can be identified.Halliburton CompanyMassachusetts Institute of Technology. Earth Resources LaboratoryMassachusetts Institute of Technology. Borehole Acoustics and Logging Consortiu

A Method of Measuring Acoustic Wave Attenuation in the Laboratory

The measurement of attenuation is performed by directly determining the attenuation operator (or the impulse response of the medium) in the time domain. In this way, it is possible to separate the attenuation operator from other non-attenuation effects, e.g. reflections. The Wiener filtering technique, or the damped least-squares, is used to calculate the attenuation operator. For the damped least squares, we have corrected for the effect due to the addition of the damping constant using a perturbation method. Numerical tests are carried out to illustrate the technique. The geometric beam spreading of ultrasonic waves generated by a source of finite size can strongly affect the result of attenuation measurements. Corrections are made by equating the received signal to the average pressure over the receiver surface. The technique is used to measure ultrasonic attenuation in water, glycerol and mud. The measurement in water offers a test of the corrections made for the geometric beam spreading. The measurement in glycerol and mud shows that, in the frequency range of 0.2-1.5 MHz, the attenuation of glycerol increases rapidly with frequency, whereas the attenuation of mud is proportional to frequency, exhibiting a constant Q behavior. The measurements show that the technique used here is an effective approach to the measurement of attenuation.Massachusetts Institute of Technology. Full Waveform Acoustic Logging Consortiu