G. I. 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.

About a mechanism of the formation of sedimentary waves on the shelf of the Sea of Japan

The existence of sedimentary waves at depths ranging from 50 to 100 m in Peter the Great Bay of the Sea of Japan has been discovered and substantiated as a result of geological and geophysical experiments. The experimental and theoretical studies have made it possible to conclude that the sedimentary waves form in the depth range specified due to processes related to the disintegration of nonlinear gravity waves.

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.

On a possibility of prognosis of crustal earthquakes by variations of the stress-strain field of the Earth

This paper discusses the prospects of application of the laser deformographs, broadband seismographs, and GPS/GLONASS receivers for the purpose of prediction of a probable crustal earthquake with magnitude 7 at the depth of 20 km by variations of the stress-strain field of the Earth on its surface. The measurement carried out have shown that the application of laser deformographs can solve this problem, while the application of various seismographs and GPS/GLONASS receivers cannot help to do this.

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.

New Data on the Deep Structure of the Northern Part of the Gulf of Tonkin in the South China Sea Based on the Results of Magnetotelluric Soundings

We present a geoelectric model for the northern part of the Gulf of Tonkin in the South China Sea, which was developed for the first time based on the data of magnetotelluric studies carried out in 2012- 2013. The existence of a regionally developed aniso� tropic conducting fractured horizon and a steeply dip� ping electrically conductive fault zones is a distin� guishing property of this model, which has a layer� block structure. The nature of the zones of electric conductivity is related to the accumulation of a water� graphite mixture during longterm propagation of the flow of deep gases, which include H 2 and CH4. This allows us to consider the outcrops of the deep fluid sat� urated fractures as potential oil bearing regions. In the conditions when traditional oil and gas deposits are being exhausted, the search for new objects of accumulation of hydrocarbons has become one of the present pressing problems. In recent years, research into fissured formations in the upper level of the basement, which is a transition complex between the crystal basement and the sedimentary cover, has become widely developed (1). The rocks related to the transition basement are almost not changed by the processes of regional metamorphism. They are dislo� cated more greatly than the overlying columns of the sedimentary cover, transformed by recrystallization processes and catagenesis, and have a different struc� tural position. The oilandgas-bearing properties of such complexes have been established in different regions of the world: East Siberia (2), Venezuela, US, Libya, Egypt, and India (3). In 1988, a unique deposit was discovered in the granites of the Mesozoic base� ment on the shelf of South Vietnam (4). Deep geophysical processes that give us the possi� bility to make a primary estimate of the structural and material characteristics of the basement in the study regions play an important role in the study of these structures. The estimate includes the existence of fis� sured complexes and locations of permeable zones in the lithosphere that provide pathways for migration of deep fluid fluxes, which are sources of saturations of the fissured complexes with hydrocarbons. All this allows us to forecast the oilandgas-bearing potential of the study region. One of the geophysical methods used for the solution of these problems is magnetotel� luric sounding, which makes it possible to study the differentiation of electric resistivity of the tectono� sphere deep section depending on its structural mate� rial composition.

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.

Some regularities in the dynamics of the periods of sea wind waves

An empirical equation on a change in the periods of wind waves at the point of recording, which makes it possible to calculate the period of wind waves in any direction on a time scale, is derived based on the experimental data.