V. V. Ovcharenko

Internal marine waves and atmospheric depressions

This work describes the results of processing experimental data during synchronous registration of the crust deformations and oscillations of atmospheric and hydrospheric pressures. It was found that internal marine waves with a frequency range from 5 to 20 min are mainly generated by atmospheric disturbances, whose variations are absolutely identical to those of hydrospheric pressure in the shelf zone of the Sea of Japan.

Recording of deformation anomaly of a tsunamigenous earthquake using a laser strainmeter

A deformation anomaly with a size of approximately 59.3 µ m caused by a tsunamigenous earthquake on December 26, 2004, was detected using a 52.5-m horizontal laser strainmeter of the unequal arm type set in Primorskii Krai of Russia. It was possible to predict a powerful tsunami wave based on the size of the deformation anomaly, which reached the strainmeter location region from the earthquake epicenter in 19 min 54 s.

Loading effect of sea level variations on the Earth’s crust

Different experimental studies in any of the com ponents of the atmosphere–hydrosphere–lithosphere transitional zone should take into account the possible erroneous interpretation of the results obtained due to lack of information about the studied processes in other geospheres. While the influence of atmospheric processes on processes in the hydrosphere is more or less well studied, the loading effect of hydrospheric processes on the level of crustal deformations is unknown, because of the uncertain structure of the Earth’s crust and because the way in which hydro spheric processes affect the Earth’s crust is almost unknown. Of course, it is known that wind driven sea waves generate microseisms of the respective periods in the crust during interacting between waves and the seafloor—it was noted as early as the 1960s by K. Has selmann [1].

Dynamics of wind waves during propagation over a shelf of decreasing depth

A laser meter of pressure variation in the hydro sphere [1, 2] and a mobile laser meter of pressure vari ations in the hydrosphere [3] were used as the laser interference receiving systems. They were included in the laser interference hardware–software complex [4, 5] deployed at different depths in Vityaz Bay of Peter the Great Gulf in the Sea of Japan along the direction of wind wave propagation (Fig. 1). The laser meter of pressure variation in the hydrosphere was deployed at a depth of 11.8 m, and the mobile laser meter of pres sure variations in the hydrosphere was set at a depth of 4.5 m. The distance between the instruments was 96 m. The information from these laser interference systems was transmitted by cable lines to the coastal station and recorded in the data bank with a sampling fre quency of 500 Hz. Later, these experimental data were processed using a specially developed programming package software Deformograf, which applied differ ent methods of obtaining spectral and statistical esti mates.

Particulars of a transmitted acoustic signal at the shelf of decreasing depth

The paper analyzes the experimental data obtained in a comprehensive experiment aimed at identifying the regularities of transmitted hydroacoustic signal transformations at the shelf of decreasing depth. The 33 Hz harmonic hydroacoustic signals were generated at the shelf of the Sea of Japan by a low-frequency source. Distribution of the transmitted energy at vertical sounding from the surface to the bottom was studied at different shelf points with Bruel & Kjaer 8104 hydrophone. At the shore, the transformed seismo-acoustic signals were received by a 52.5 m shore laser strainmeter. The experiments showed that about 22% of the transmitted energy was transformed into the energy of hydroacoustic waves propagating in the water. About 72% of hydroacoustic wave energy, in turn, was transformed into the energy of R-waves, which were registered by the shore laser strainmeter. Other regularities of hydroacoustic signals distribution with 33 Hz frequency over the V-shaped shelf are identified.

Development of tomographic technology for the Earth’s crust in the shelf regions

On the basis of experimental data obtained during a comprehensive experiment in Vityaz Bay of the Sea of Japan using onshore laser strainmeters and a low-frequency hydroacoustic emitter generating complex phase-manipulated signals with a central frequency of 33 Hz, we developed the basic principles of contactless tomography of the Earth’s crust in the shelf regions of various seas, including those covered by ice, making it possible to determine efficiently the structure and composition of the upper Earth’s crust under seas.

Peculiarities of spreading of acoustic waves over a shelf with decreasing depth

We analyze experimental data collected in Vityaz Bay of the Sea of Japan during study of the peculiarities of spreading of hydroacoustic waves over a shelf with decreasing depth. We found that the waves propagate over a shelf with depths greater than half of the hydroacoustic wave according to the law of cylindrical divergence with least losses of the wave energy. If the depths are shallower than half of the hydroacoustic wave, they spread along the water-bottom boundary as Rayleigh waves of decaying and undamped types with significant absorption of the wave energy by the bottom.