Laser Strainmeter Research Articles

Estimation of Free Core Resonance Parameters Based on Long-Term Strain Observations in the Diurnal Frequency Band

The free core nutation (FCN) is one of the Earth’s rotational eigenmodes, which is caused by the retrograde motion of the liquid core relative to the mantle. The FCN period and Q-factor are determined by the elastic properties of the core/mantle boundary (CMB) and their electromagnetic interaction. In the celestial coordinate system, the FCN period is about 430 days; in the Earth-fixed reference frame this effect manifests itself in the form of the free core resonance (FCR) whose frequency falls in the diurnal tidal band. FCR observation requires highly accurate measurement of the amplitudes and phases of the near-diurnal tidal waves. In particular, the parameter estimates for minor waves K1, P1, Ψ1, and Φ1 are critically important for evaluating the FCR effect, i.e., the period and decay of this resonant mode. The progress in the experimental study of FCR is mainly due to the accumulation of the data from superconducting gravimeters and VLBI; at the same time, also the data of the precision laser strainmeters were used. In this work, the FCR effect is studied based on the long-term strain precision records by two European stations: Baksan, Russia (laser interferometer–strainmeter with a measuring armlength of 75 m [Milyukov et al., 2005; 2007] and Gran Sasso, Italy (two perpendicular laser interferometer–strainmeters, BA and BC, each with a measuring armlength of 90 m [Amoruso and Crescentini, 2009]).

Assessment of the geomechanical state of the rock mass in the Streltsovsk ore field region according to high-precision deformation measurements

The paper presents a measuring set – a single-component laser strainmeter – for geodynamic monitoring within the Streltsovsk ore field. The results of experimental studies with the participation of a laser strainmeter (deformograph) are presented and the influence of external factors on the state of the massif has been estimated. The influence of distant earthquakes on the state of the mountain massif has been estimated. The features of the deformation field behavior during preparation and implementation of a rock burst have been noted. Characteristics of rock burst precursors in the low-frequency measurement region have been given.

A Laser Interference System for Detecting Gravitational Waves

New principles of a gravitational wave detection system based on the use of pendulum-type laser strainmeters (LSMs) spaced by a large distance are discussed. By arranging three pendulum-type LSMs with 1000-m arm lengths on 316-km sides of equilateral triangle, it is possible to provide for the threshold sensitivity of this system within up to the 23rd decimal point in a frequency interval from 3 to 950 Hz for detecting extraterrestrial signals propagating at the speed of light.

Correlation of Aerosol Scattering Lidar and Laser Strainmeter Signals during Earth’s Crust Deformations

Lidar sensing of tectonic aerosol fluctuations in the laser strainmeter–interferometer tunnel during 2017.12–2018.05 at the Schultz cape (131°9′8″ E, 42°34′6″ N) near Vladivostok was performed for the first time to our knowledge. A negative correlation of laser interferometer and aerosol lidar signals was observed during low-frequency Earth crust deformations.

The Nature of the “Voice of the Sea”

Strong vibrations of the Earth’s crust in the frequency range of 7–9 Hz, referred to as the “voice of the sea,” have been recorded in the course of processing synchronous experimental data obtained during recording of variations in the deformation of the Earth’s crust using a shore laser strainmeter, atmosphere pressure variations using a laser nanobarograph, and hydrosphere pressure variations using a laser meter for hydrospheric pressure and wind velocity variations. The nature of these vibrations and their transformation to adjacent geospheres have been discussed.

Лазерно-интерференционная система детектирования гравитационных волн

AbstractNew principles of a gravitational wave detection system based on the use of pendulum-type laser strainmeters (LSMs) spaced by a large distance are discussed. By arranging three pendulum-type LSMs with 1000-m arm lengths on 316-km sides of equilateral triangle, it is possible to provide for the threshold sensitivity of this system within up to the 23rd decimal point in a frequency interval from 3 to 950 Hz for detecting extraterrestrial signals propagating at the speed of light.

Deformation-Electromagnetic Relations in Lithospheric Activity Manifestations

It has been shown that dipole radiation of accelerated charges, described by Larmor relation, is the basis of the known mechanic-electromagnetic processes of rock deformation. Comparison of crust deformation acceleration with natural electromagnetic field parameters of ELF-VLF range showed good relation. It manifests in the maxima of occurrence frequency density of synchronous deformation-electromagnetic events on two dimensional histograms. The data of a laser strain-meter and a recorder of natural electromagnetic radiation of ELF-VLF range, recorded in a zone of increased seismic activity (Kamchatka, Karymshina site), were used. The authors made an assumption on the existence of stationary regions of deformation process and mechanic-electromagnetic transformations corresponding to regions with different mechanic properties and rock petrographic composition.

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.

Application of the Empirical Mode Decomposition in Deformation Monitoring in Mines

The method of the empirical mode decomposition and its application to the analysis of data obtained using a laser strain meter is described. The issues of adaptation of the method to real data are discussed. The method enables identification of a monotone trend and a slow component of deformation process much more efficiently than the conventional techniques. The method shows reliable operation in cleaning of signals from noise and high frequencies.

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.

A non-destructive non-contact method of the sea-bottom structure investigation

The paper describes a nondestructive noncontact method for investigating the sea-bottom structure using hydroacoustic and laser radiation. A practical implementation of this method is also presented. The research complex incorporates a state-of-the-art low-frequency hydroacoustic radiating system and a system of coastal laser strainmeters arranged in the specially selected sea waters and coastal grounds. The hydroacoustic radiators are used to generate a seismic signal. Seismic superficial waves are recorded by the coastal laser strainmeters. Optical parts of the strainmeters are constructed as the unequal-path Michelson interferometer where the frequency-stable helium-neon lasers serve as emission sources. A preliminary model of the sea-bottom testing ground has been developed by application of geologic-geophysical procedures. The model-based analysis of the timing data of the recorded seismic waves was carried out. The prospectivity of the used method was proved.

Data Logging and Transmission System for Laser Strainmetering Equipment

The authors have designed a multi-purpose multi-channel data recording and transmission system for the laser strainmeters and the related geophysical and seismic equipment intended for service in operating mines.

Two High-Sensitivity Laser Strainmeters Installed in the Canfranc Underground Laboratory (Spain): Instrument Features from 100 to 0.001 mHz

Two laser strainmeters are being operated in the Canfranc Underground Laboratory (LSC, Central Pyrenees, Spain) at about 350 m depth. One of the two laser strainmeters (GAL16, striking 76°) is located about 670 m from the Spanish entrance of a decommissioned train tunnel, along the side wall of one of the bypasses connecting a recent highway tunnel to the train tunnel. The other strainmeter (LAB780, striking -32°) is located about 780 m from the Spanish entrance of the train tunnel, inside two narrow side halls parallel to and built at the same time as the train tunnel. Their mechanical and optical setups derive from a previous installation at Gran Sasso, Italy, with some changes and improvements. Here we show the main instrument features in the frequency range of 100–0.001 mHz. At frequencies lower than 4 mHz, strain noise compares well with the best laser strainmeters made till now, while at higher frequencies strain noise is higher than at Kamioka, Japan, probably because of frequency instabilities of the laser source. Environmental (air temperature and pressure) effects on measured strain are quite small; thus, signal-to-noise ratio in the tidal bands is unusually high. In particular, diurnal Ψ1 and Φ1 tides clearly emerge from noise even using a 2-year-long strain record, giving the opportunity to improve previous determinations of the Free Core Nutation parameters from strain data as soon as more data are acquired. The features of the LSC strainmeters allow investigating the Earth in a very broad frequency range, with a signal-to-noise ratio as good as or better than that of the best laser strainmeters in the world.

A Cost-Effective Geodetic Strainmeter Based on Dual Coaxial Cable Bragg Gratings.

Observations of surface deformation are essential for understanding a wide range of geophysical problems, including earthquakes, volcanoes, landslides, and glaciers. Current geodetic technologies, such as global positioning system (GPS), interferometric synthetic aperture radar (InSAR), borehole and laser strainmeters, are costly and limited in their temporal or spatial resolutions. Here we present a new type of strainmeters based on the coaxial cable Bragg grating (CCBG) sensing technology that provides cost-effective strain measurements. Two CCBGs are introduced into the geodetic strainmeter: one serves as a sensor to measure the strain applied on it, and the other acts as a reference to detect environmental noises. By integrating the sensor and reference signals in a mixer, the environmental noises are minimized and a lower mixed frequency is obtained. The lower mixed frequency allows for measurements to be taken with a portable spectrum analyzer, rather than an expensive spectrum analyzer or a vector network analyzer (VNA). Analysis of laboratory experiments shows that the strain can be measured by the CCBG sensor, and the portable spectrum analyzer can make measurements with the accuracy similar to the expensive spectrum analyzer, whose relative error to the spectrum analyzer R3272 is less than ±0.4%. The outputs of the geodetic strainmeter show a linear relationship with the strains that the CCBG sensor experienced. The measured sensitivity of the geodetic strainmeter is about −0.082 kHz/με; it can cover a large dynamic measuring range up to 2%, and its nonlinear errors can be less than 5.3%.

The nature of terrestrial infragravitational “noise”

This paper is focused on analysis of comprehensive experimental research data on the infragravitational range of periods (from 20 s to 10–12 min) obtained by synchronous measurements of fluctuations in deformations of the Earth’s crust and atmospheric and hydrospheric pressure variations. It is established that the identified variations in the period range of 1–4 min are rarely observed in records of a laser nanobarograph and laser instrument for measuring hydrospheric pressure variations (laser hydrophone), while they are frequently observed in records of laser strainmeters at a variation period of 3–4 min. Oscillation excitation in the period ranges of 7–13 min, especially in the period ranges of 8–12 min, is largely related to atmospheric processes in the corresponding periods.

A 50-m laser strainmeter system installed in Transbaikalia: testing results

We report testing results for a 50-m laser strainmeter installed 300 m under the ground in a mine of PJSC Priargunsky Industrial Mining and Chemical Union (Krasnokamensk) and demonstrate its ability to record microseisms and waves of infrasonic-sonic bandwidths. Processing and interpretation of the collected data provides information about microseismic to tidal strain changes in the Transbaikalian region.

Laser strainmeter in integrated geodynamic monitoring within Streltsov Ore Field

The authors describe operation of a laser strainmeter within the integrated geodynamic monitoring system in Streltsov Ore Field. Capabilities and design features of the strainmeter are discussed. The article demonstrates feasibility of highly accurate measurements of deformation field parameters in an operating mine. Specificity of natural oscillations of the Earth is defined, and deformation of rock mass depending on energy of a destruction source is evaluated.

Nonlinear and minor ocean tides in the Bay of Biscay from the strain tides observed by two geodetic laser strainmeters at Canfranc (Spain)

AbstractThis work presents and discusses the tidal analysis of about 2.5 years of strain data recorded by two 70 m‐long high‐resolution laser strainmeters, which are operating in the Canfranc underground laboratory (Central Pyrenees, Spain). Spectra show clear tidal peaks whose frequencies range from the diurnal band to at least 8 cycles per day; strain amplitudes (relative change in length for each strainmeter) range from few to . The reliability of observations and corrections for local distortions are testified by the excellent agreement between measurements and computations for all the diurnal and semidiurnal tides included in the TPXO8 and FES2012 tidal atlases, with the exception of L2. Observed higher‐frequency strain tides are mostly attributed to loading by nonlinear shallow‐water constituents in the Bay of Biscay, more than 120 km from the measurement site. The signals are quantitatively compared with computations using TPXO8 (MN4, M4, and MS4) and FES2012 (M3, N4, MN4, M4, MS4, and M6). Computations fully agree with M4 observations for one strainmeter, overestimate M4 by about 30% for the other strainmeter and M6 by about a factor of two, and underestimate the other tides. This work shows that data from high‐sensitivity strainmeters installed in high‐quality sites may provide valuable additional information for studying the nonlinear tidal dynamics and energetics of coastal waters and minor ocean tides, at spatial resolutions of tens to thousands square kilometers, depending on the strainmeter location with respect to the coastline.

Comparing a new laser strainmeter array with an adjacent, parallel running quartz tube strainmeter array.

In summer 2011, two new laser strainmeters about 26.6 m long were installed in N-S and E-W directions parallel to an existing quartz tube strainmeter system at the Geodynamic Observatory Moxa, Thuringia/Germany. This kind of installation is unique in the world and allows the direct comparison of measurements of horizontal length changes with different types of strainmeters for the first time. For the comparison of both data sets, we used the tidal analysis over three years, the strain signals resulting from drilling a shallow 100 m deep borehole on the ground of the observatory and long-period signals. The tidal strain amplitude factors of the laser strainmeters are found to be much closer to theoretical values (85%-105% N-S and 56%-92% E-W) than those of the quartz tube strainmeters. A first data analysis shows that the new laser strainmeters are more sensitive in the short-periodic range with an improved signal-to-noise ratio and distinctly more stable during long-term drifts of environmental parameters such as air pressure or groundwater level. We compared the signal amplitudes of both strainmeter systems at variable signal periods and found frequency-dependent amplitude differences. Confirmed by the tidal parameters, we have now a stable and high resolution laser strainmeter system that serves as calibration reference for quartz tube strainmeters.

Recording seismoacoustic signals of a surface vessel with a two-coordinate strainmeter

Experimental data are analyzed, obtained during the recording of seismoacoustic signals with a two-coordinate laser strainmeter; the signals were generated by a surface vessel moving over the shelf and deep water. Based on analysis of the obtained data, we substantiate the prospect of applying shore-based laser strainmeters for the direction finding of vessels and the creation of monitoring systems for large water areas.