Vladimir I. Talanov

Observation of slow dynamics effects in nonconsolidated media under in situ conditions

Reactions of an unconsolidated medium to a strong impact action are considered. A character of medium relaxation was controlled based on changes in the phase velocity of a trial Rayleigh wave. The analysis of the R-wave dispersion and its dependence on the distance to the source allowed for estimating the dimensions of a space region where the impact action was revealed. Seismoacoustic measurements showed that the time dependence of the R-wave is logarithmic.

Diagnostics of the acoustic properties of unconsolidated media under natural conditions

Results of experimental studies carried out at the Bezvodnoe test area in 2005 and 2006 are presented. The goal of the studies is to investigate the potentialities of vibration diagnostics of the surface layers of soil under natural conditions. The most attention is given to the problem of measuring the shear modulus of soil and determining the power of seismic acoustic radiation with the help of an impedance method. The results obtained testify to the high sensitivity of the impedance method soil diagnostics and to the possibility of monitoring the variations of soil properties. Sources of nonlinear distortions and the problem of stability of radiation characteristics are also considered. A comparison with theoretical estimates is performed. It confirmed a special role of the contact region as the major source of radiation signal distortions. The results of the study are important for seismoacoustic investigation of the structure of natural media under natural conditions.

Experimental investigation of potentialities of seismoacoustic sea-bottom sounding using coherent pulse signals

We describe the results of experimental investigations of the seismoacoustical sounding of the bottom structure of the Caspian Sea. They were obtained using a ship towed hydroacoustic emitter of LFM pulse signals in several frequency ranges of frequency band from 100 to 1000 Hz. Based on the high coherence and relatively high frequencies of emitted signals, the results point to feasibility of substantial improvement in noise immunity and resolution of sounding the bottom rocks’ structure at depths of up to 1000 m thanks to combined application of a series of procedures of coherent processing of incoming signals. The processing involves matched filtering of individual pulses, coherent accumulation of pulse trains within the horizontally uniform bottom area, and adaptive path accumulation of pulses accounted for inclination of individual reflecting layers. The resulting gain in noise immunity came to about 30 dB, which points to possibility of efficient use of relatively low-power (up to 100 W) coherent sources for seismoacoustic sounding of sea bottom at minimal damage to local ecology.

In situ estimation of crack concentration in hard rock

Results of a 2004 field experiment aimed at determining the quadratic nonlinearity parameter in granite that forms the shore of the Ladoga lake are presented. The measurements were based on the observation of the nonlinear interaction between monochromatic waves excited by two hydroacoustic radiators of 1 kW each positioned near the shore. The initial level of nonlinear distortions was much lower than the level of the received difference-frequency signal. The quadratic nonlinearity parameter proved to be higher than that reported in the majority of publications. An assumption was put forward that the high nonlinearity of granite is caused by the high concentration of cracks in it. Pieces of rock were taken from the measurement site, and rectangular samples were prepared from them. The samples were studied by the acoustic spectroscopy method in laboratory conditions. As a result, estimates of crack concentration were obtained, which proved to be consistent with the field measurements of the quadratic nonlinearity parameter. Thus, the possibility of estimating the crack concentration in situ from the measurements of the quadratic nonlinearity parameter was demonstrated.

Phase method of crosswell profiling using coherent SH waves

The results of an experiment on crosswell profiling using the coherent downhole source of SH waves are presented. Seismic records were obtained during stationary disposal of the source and varying depths of the vector receiver position. The source coherence made it possible to accumulate signals, thus sub-stantially improving the quality of seismograms and measuring phases. These procedures allowed low-contrasting boundaries between layers to be distinguished. The performed digital modeling confirmed the measurement results.

Application of hydroacoustic radiators for the generation of seismic waves

To excite seismic waves with a high coherence, powerful hydroacoustic radiators placed in a natural reservoir were used. Theoretical estimates and the test data demonstrate a high efficiency of the proposed method of seismic wave excitation. The calculations are in good agreement with the results of measurements. The results of phasing the radiation with the use of two monopole sources separated by a quarter-wave distance are presented. It is shown that the use of the proposed scheme of excitation makes it possible to control the radiation pattern while obtaining a high coherence of seismic waves.

A new method for reconstructing medium inhomogeneities using Rayleigh waves: Case studies

The problem of reconstructing local low-contrast inhomogeneities in the Earth’s surface layers by means of coherent Rayleigh surface waves is considered. It is shown that analysis of the frequency characteristics of shear projections in this wave on the surface allows construction of the function of inhomogeneity distribution in a specified depth range. The results from seismoacoustic reconstruction of inhomogeneities correlate with data obtained using standard geophysical methods and are confirmed by direct observations.

Acoustic nonlinearity of granite: Comparison of data of field and laboratory experiments

The paper presents the results of laboratory measurements of the acoustic nonlinearity parameter for a granite sample from the site of a conducted field experiment. This made it possible to completely confirm the results of the field experiment and explain the occurrence of a large scatter of values for the nonlinearity parameter in the field measurements. The size of the quadratic linearity parameter in granite rocks was determined, normalized to the volumetric concentration of fractures, which can be used for remote estimation of the fracture concentration.

A high-power intrawell radiator of shear waves for coherent seismoacoustics

A brief review of investigations in the field of coherent seismoacoustics is presented, and the general requirements for seismoacoustic wave radiators intended for solving problems of remote sounding are formulated. The principle of operation of a novel high-power radiator created at the Institute of Applied Physics, Russian Academy of Sciences, for generating low-frequency seismic waves is described, and the results of the analytical and numerical modeling of this radiator are presented. The main element of the radiator is a piezoelectric cylinder executing bending vibrations in a well filled with water. The concept of sectioning the radiating cylinder for increasing the efficiency of excitation of various radiator modes and improving the matching the radiator with the medium is formulated. The results of the field measurements of the space-time structure of the seismic field generated by the sectioned radiator are presented. On the basis of these measurements, estimates of the power, efficiency, and quality factor of the radiator are obtained.

Seismoacoustic survey of artificial inhomogeneities in the ground

The results of processing the field test data obtained for the seismoacoustic system designed at the Institute of Applied Physics of the Russian Academy of Sciences for the visualization of underground engineering structures are presented. The described experiment is the first demonstration of the use of a high-power, high-stability transmitting-receiving system for producing a coherent insonification with a frequency of 195 Hz. The receiving element of the system is a synthetic aperture array. With the use of focusing as a method of the final signal processing, an image of a tunnel lying at a depth of 30 m is obtained in three spatial cross-sections, which demonstrates the possibility of a three-dimensional, coherent, high-frequency seismic survey of engineering structures.