S. G. Dolgikh

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.

Seismoacoustic Hydrophysical Complex for Monitoring the Atmosphere–Hydrosphere–Lithosphere System

The seismoacoustic hydrophysical complex intended for investigation of the interaction of geospheres wave fields in a frequency range from 1 μHz to 1 Hz is described. The complex consists of a shore-based system of laser strain meters, laser nanobarograph, bottom station with a hydrophone and a temperature-sensitive element, weather station, and seismoacoustic radiator. The use of modern laser-interferometry methods provided a deformation sensitivity of ∼10–10 and an atmospheric-pressure sensitivity of 10 mPa.

The feasibility of laser strainmeters for sea floor diagnostics

Based on experimental works devoted to study of a lowfrequency (central frequency is 33 Hz) emitter and shorebased laser strainmeter for investigation of the Earths crust structure and definition of the main elastic properties of rocks on emitter-receiver paths, it has been shown that application of these instruments with an increase in the power of receivers and a tunable central frequency of radiation is a promising feature due to the broad operational frequency range and high sensitivity of the laser strainmeters. As is known (1-3), in the low frequency region, seismoacoustic surface waves become the dominating mechanism of acoustic energy transport in the shelf zone, and this feature can be used during experiments on study of the crustal structure within shelf zones of different seas. Since the frequencies of signals emitted by lowfrequency hydroacoustic emitters are about 20-35 Hz (i.e., wavelengths in water are about 75- 40 m, and about 150-100 m in the solid medium at an elastic wave velocity of about 3000 m/s), the depth of the signal penetration into the Earths crust is signifi� cant. All soundings of sediments or water medium are implemented using the technique of signal investiga� tion at the chosen frequencies and their reception by various, preferably broadband, receivers. Broadband receiver systems are used in order to avoid probable distortion of the received information. The time inter� vals between emission and reception time must be measured very accurately in order to obtain the appro� priate thicknesses of studied layers, but this cannot be done if harmonic or pulsed signals are used. In the studies of this kind, complex, phaseshift signals (M� sequences) are preferred; their application in hydroa� coustic and seismoacoustic tomography and inversion studies allows specialists to define the arrival times with a high accuracy. Additionally, signal attenuation does not affect the processing result significantly, because the main processing stage is not related to spectraltemporal investigation of the signal behavior, but to convolution of the received and emitted signals. This peculiarity makes this technique feasible even with significant noise, whose amplitude can exceed that of the received hydroacoustic or seismoacoustic signals.

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].

Studying the variability of the wind wave period

Analyzed are the experimental data on the range of the sea wind waves obtained using a laser meter of hydrospheric pressure variations in 2007, 2010, 2011, and 2012 at different points of the shelf of the Sea of Japan. It is demonstrated that the variations of wind wave periods at their leaving the zone of cyclonic action can be associated not only with the dispersion but also with the Doppler effect and variations of the wind speed and wind direction in the zone of cyclonic action. Carried out was the analysis of the results of the processing of experimental data of the laser meter of hydrospheric pressure variations and the mobile laser meter of hydrospheric pressure variations; this analysis revealed that the transformation of wind waves with the decrease in the period and energy takes place in the case of their movement along the shelf of the decreasing depth.

A hydrophysical laser-interference complex

An upgraded laser measurer of hydrosphere pressure variations is described. By mounting new pressure and temperature sensors and optimizing the design of the submersible instrument, it has become possible to considerably increase the measurement accuracy of amplitude−frequency characteristic describing variations in the pressure, aqueous medium temperature, and wave amplitudes at the sea surface in the infrasonic and audio ranges and to correct plotted time dependences of the pressure variations in view of the variations in the interferometer and outboard water temperatures. For long-term (up to 40 h) self-contained operation of the complex to be guaranteed, a versatile floating container has been developed. This container is equipped with high-power batteries and data acquisition systems receiving information from the sensors and can be joined to a hermetically sealed connector of the complex instead of the cable line used for communication between the complex and coast equipment.

Compensation for the temperature effect on operation of laser interferometers

A temperature-compensated design of laser meters of hydrosphere pressure variations and laser hydrophones has been developed and introduced. Owing to this design, it is possible to perform long-term measurements without tuning the optical section of an instrument.

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.

Laser meter for hydrosphere pressure variations with a mechanical temperature compensation system

Based on modern laser interferometric methods, a laser meter has been developed, equipped with a mechanical external thermal effect compensation system designed to record hydrospheric pressure variations in the frequency range from 0 (conventionally) to 1000 Hz with an accuracy of 50 μPa.