Laser Strainmeter Research Articles

Deep‐Learning Based Causal Inference: A Feasibility Study Based on Three Years of Tectonic‐Climate Data From Moxa Geodynamic Observatory

AbstractHighly sensitive laser strainmeters at Moxa Geodynamic Observatory (MGO) measure motions of the upper Earth's crust. Since the mountain overburden of the laser strainmeters installed in the gallery of the observatory is relatively low, the recorded time series are strongly influenced by local meteorological phenomena. To estimate the nonlinear effect of the meteorological variables on strain measurements in a non‐stationary environment, advanced methods capable of learning the nonlinearity and discovering causal relationships in the non‐stationary multivariate tectonic‐climate time series are needed. Methods for causal inference generally perform well in identifying linear causal relationships but often struggle to retrieve complex nonlinear causal structures prevalent in real‐world systems. This work presents a novel model invariance‐based causal discovery (CDMI) method that utilizes deep networks to model nonlinearity in a multivariate time series system. We propose to use the theoretically well‐established Knockoffs framework to generate in‐distribution, uncorrelated copies of the original data as interventional variables and test the model invariance for causal discovery. To deal with the non‐stationary behavior of the tectonic‐climate time series recorded at the MGO, we propose a regime identification approach that we apply before causal analysis to generate segments of time series that possess locally consistent statistical properties. First, we evaluate our method on synthetically generated time series by comparing it to other causal analysis methods. We then investigate the hypothesized effect of meteorological variables on strain measurements. Our approach outperforms other causality methods and provides meaningful insights into tectonic‐climate causal interactions.

Twenty-Meter Laser Strainmeter "Popova Isl."

This paper describes the design and principle of operation of a 20 m laser strainmeter of unequal-arm type created on the basis of a Michelson interferometer and frequency-stabilized helium-neon laser. The interferometry methods used allow the measurement of the displacement of an Earth's crust section on the base of the laser strainmeter with an accuracy of 30 pm in the frequency range from 0 (conventionally) to 1000 Hz. This laser strainmeter, when connected to an accurate time system providing an accuracy of 1 μs, should structurally become a part of the laser interferometric seismoacoustic observatory, consisting of spatially separated laser strainmeters installed in various regions of Russia.

Hard- and Software Controlled Complex for Gas-Strain Monitoring of Transition Zones.

The article describes a hard- and software controlled complex for gas-strain monitoring, consisting of stationary laser strainmeters and a laser nanobarograph, a stationary gas analyzer, and a weather station installed at Shultz Cape in the Sea of Japan; and a mobile shipboard complex, consisting of a gas analyzer and a weather station installed in a scientific research vessel. In the course of trial methodological measurements on these systems, general patterns were identified in the dynamics of greenhouse gases and deformation of the Earth's crust in the range of diurnal and semi-diurnal tides, and also in the range of ultra-low frequencies, caused by atmospheric wave processes and, possibly, individual tones of the Earth's eigen oscillations.

Temporary slip speed increases during short-term slow slip events with durations of one to three hours

AbstractTemporary slip speed increases with durations of 1–3 h were identified during short-term slow slip events in records of borehole and laser strainmeters in the Tokai region, Japan. They were found by searching for peaks of correlation coefficients between stacked strain data and ramp functions with rise times of 1 and 2 h. Although many of the strain steps were considered due to noise, some strain steps occurred with simultaneous activation of the deep tectonic tremors and shared source areas with the tremors. From 2016 to 2022, we observed five strain steps with simultaneous activation of tectonic tremors and coincidence of source locations with the tremors. Those strain steps occurred during short-term slow slip events and were temporary slip speed increases of the slow slip events. Those strain steps seemed to be related to successive occurrences with source migration of short-term slow slip events. The detrended strain steps corresponded to plate boundary slip events of moment magnitude around 5, which was consistent with the scaling law of slow earthquakes. Graphical Abstract

IONOSPHERIC DISTURBANCES OVER PRIMORSKY KRAI CAUSED BY THE ERUPTION OF THE HUNGA TONGA-HUNGA HA’APAI VOLCANO ON JANUARY 15, 2022

The explosive eruption of the Hunga Tonga-Hunga Haapai volcano occured on January 15, 2022 at 04:02 UTC led to generation of covolcanic ionospheric disturbances that spread over long distances. Using GNSS data obtained at permanent stations of the IGS network and sites located on the territory of Primorsky Krai, the search and analysis of ionospheric disturbances over the territory of Primorsky Krai and adjacent areas was performed. The velocity of the covolcanic ionospheric disturbances recorded over the Primorsky Krai reached about 340 m/s, and the average amplitude was equal to 1.0 TECU. The results obtained from GNSS-data were also compared with the results of observation data obtained by a laser strainmeters (oriented in the directions "north – south" and "east – west") and a laser nanobarograph located at the Schultz Cape (the south of Primorsky Krai). As a comparison result, time delays between the moments of fixation of disturbances in the troposphere and ionosphere were found. The delay between the first peaks of disturbances was equal to ~50 min.

Deformation Anomalies Accompanying Tsunami Origins near the Japanese Islands

In the paper, we analyze laser strainmeter data for the period from 2014 to 2022 to identify deformation anomalies that led to the generation of tsunamis in the area of the Japanese Islands. It is impossible to determine the main characteristics of a tsunami from the deformation anomaly registered by the laser strainmeter, but it is possible to calculate the seabed displacement in the epicenter of a tsunami formation, which causes the tsunami. We have established that the relationship between the registered deformation anomalies and the seabed displacement in the tsunami source in the area of the Japanese Islands is similar to the same relationships found in other regions of the Earth (Indonesia, Latin America, and the West Coast of North America). This result allows us to assert that such a relationship should be typical of any region of the Earth. The obtained results are aimed at solving the problem of reliable short-term tsunami forecasting, which allows for the avoidance of false alarms that lead to significant socio-economic damage.

Microseismic oscillations as an indicator of tropical cyclones

The paper presents the results of recording microseismic oscillations in the frequency range of infrasonic waves performed during the periods of active influence of tropical cyclones on the water area of the Sea of Japan. The data were obtained by a coastal laser-interference measuring complex consisting of a two-axis laser strainmeter and a laser nanobarograph. A case study using remote sensing data shows that the world meteorological agencies stopped tracking the typhoon too early, while the cyclone retains its vortex structure and energy characteristics. The dynamics of changes in the characteristics of infrasound microseismic oscillations, which depend on the trajectory of typhoons and the duration of their impact on the sea area, is shown. Generalised results are given for some groups of typhoons having similar trajectories of movement, as a result of which the maximum amplitudes of microseismic infrasonic oscillations are manifested at different frequencies. During the passage of a category 5 typhoon in 2022, a microseismic signal formed by the interaction of the atmospheric vortex in the rear part of the cyclone with the field of quicksand waves was registered near the measuring site. As a result of registration by ground-based remote sensing methods of certain characteristics of microseismic signals generated during the passage of typhoons, it is possible to use the information to determine the parameters of tropical cyclone movement.

Inter-geosphere interaction in the infrasonic range

On the basis of experimental data from laser strainmeters, a laser nanobarograph, and a laser meter of hydrosphere pressure variations, we studied inter-geosphere interaction in microseismic range (2–20 s) and in minute range (4–17 min). We established general patterns of transformation of the Earth’s crust upper layer oscillations into atmospheric oscillations, and atmospheric oscillations—into oscillations of the Earth’s crust upper layer in the specified ranges. Besides, we show that transformation coefficient has seasonal dependence, associated with different elastic characteristics of the Earth’s crust upper layer in winter and summer due to negative winter temperatures and high positive summer temperatures, and also different moisture saturation of the soils.

Dynamics of Upper-Frequency-Range Infrasonic Wave Generation in the Northwestern Part of the Sea of Japan

The Pacific Northwest region is significantly affected by tropical cyclones, which pose a threat to humans due to strong winds and intense precipitation. Observations have shown that international meteorological agencies lower the hazard class of typhoons too early, or even stop tracking them altogether. We studied the results of in situ measurements of infrasonic microseismic oscillations in the upper frequency range, generated in the shelf area of the northwestern part of the Sea of Japan as a result of the long-term influence of strong tropical cyclones on the sea area. The measurement data were obtained using coastal laser strainmeters, which are components of the seismoacoustic hydrophysical measuring complex. The dynamics of upper-frequency-range infrasonic microseismic signals during the movement of Typhoon Chan-Hom 2015 in the Sea of Japan are shown. The same infrasonic microseismic oscillations excited by Typhoon 2022 Hinnamnor, which had no impact on the measuring station, have a difference in the width of the signal spectrum and frequency shift with maximum amplitude compared to the signals from Typhoon Chan-Hom.

Nonlinear Interaction of Infragravity and Wind Sea Waves

In this paper, the authors analyze data obtained from a supersensitive detector of hydrosphere pressure variations which was positioned on the shelf of the Sea of Japan at a depth of 25 m for several months. When processing this data, the main attention was paid to studying nonlinear hydrophysical disturbances of “rogue waves” type: “one sister”, “two sisters”, “three sisters”, and “potential well”, the origin of which is associated, apparently, with the interaction of the hydrophysical wave field in gravity range and disturbances in the infragravity range. Analysis of synchronous data of the laser strainmeter and laser nanobarograph, installed at Shultz Cape, with synchronous records of the supersensitive detector of hydrosphere pressure variations confirmed these conclusions.

Ground strains induced by the 2022 Hunga-Tonga volcanic eruption, observed by a 1500-m laser strainmeter at Kamioka, Japan

In this study, we detected the horizontal ground strains induced by the atmospheric Lamb wave emitted from the 2022 eruption of the Tonga–Hunga Ha’apai undersea volcano, at an underground observatory in Kamioka, Japan. The observed strains were in the range of {10}^{-11}–{10}^{-10} and were measured precisely using a 1500-m laser strainmeter with a high resolution in the order of {10}^{-12}. This was one of the first observations of a Lamb wave using a laser strainmeter. The strainmeter was constructed in a tunnel of the KAGRA gravitational-wave telescope. Our observations demonstrate that strain and atmospheric pressure were clearly correlated, resulting in a regression coefficient of - left(2.3-3.7right)times {10}^{-10} strain/hPa. This finding was compared with the responses under regular pressure conditions and the estimations obtained using the local deformation and traveling wave models. The observed coefficients for the Lamb wave exhibited smaller magnitudes than those observed under regular conditions and take values between that of the two theoretical models. These results reflect the intermediate scale of the pressure distribution of the Lamb wave between the assumptions of the simple models. The strain variations were also found to have started earlier than the corresponding pressure changes at the observation site with characteristic time lags ranging from 25 to 155 s. In addition, several aspects related to the mechanism that created the time lags are discussed.Graphical

Remote Seismoacoustic Monitoring of Tropical Cyclones in the Sea of Japan

In the course of processing and analysing data from a two-coordinate laser strainmeter, obtained during the propagation of the Hagupit typhoon over the Sea of Japan, we researched the possibility of sensing the direction of tropical cyclones/typhoons and also tracking their movements. We tackled the set of problems on the basis of further development of the technology for sensing the direction of primary and secondary microseisms’ generation zones, the “voice of the sea” microseisms, and clarifying the connection between their formation zones and movement of tropical cyclones. In our work, we identified the formation zones of primary and secondary microseisms, which were registered by the two-coordinate laser strainmeter. We established that, from the registered microseisms, we could determine the main characteristics of wind waves generated by a typhoon, but we could not identify its location. By processing the two-coordinate laser strainmeter data in the range of the “voice of the sea” microseisms, we established the possibility of sensing the direction of the “voice of the sea” microseisms’ formation zones, which are associated with zones of the highest energy capacity of typhoons, and this allowed us to tracking the direction of the typhoons’ movement.

Eye-safe photon counting LIDAR for magmatic aerosol detection

An eye-safe photon counting light detection and ranging (LIDAR) instrument has been developed for magmatic aerosol sensing in real time. The developed LIDAR was based on a pulsed diode laser (transmitter, 910 nm, 3 ns, <1 µJ cm−2) and a single-photon avalanche photodiode. The instrument was designed to fit the requirements of highly sensitive sensing of aerosol dynamics at distances up to 50 meters. The accuracy of the LIDAR instrument ranging was estimated as 18 cm. Field experiments inside the Baksan Neutrino Observatory tunnel above the volcano Elbrus chamber revealed a good correlation between the magmatic aerosol dynamics and the Earth’s crust deformation due to Moon and Sun tides quantified by a tiltmeter and a laser strainmeter.

Results From a Decade of Optical Fiber Strainmeters at Piñon Flat Observatory

AbstractOptical fibers, stretched between anchors attached to the Earth and buried in boreholes and shallow trenches, offer an inexpensive and robust means to observe Earth strain. We have deployed several optical fiber strainmeters (OFSs) in boreholes, where thermal stability helps mitigate the noise from temperature changes. We have also constructed horizontal OFSs in 1‐m‐deep trenches of lengths 221 and 174 m. In these, a second optical fiber having a contrasting temperature coefficient provides a means to separate true strain from thermal noise. Signals in the seismic band from the horizontal strainmeters agree well with records from collocated seismometers, and the predominant ambient noise recorded by both techniques are consistent. Solid Earth strain tides with amplitude of 30 nε (nanostrain) are observed in these horizontal OFSs that agree well with those observed by collocated vacuum laser strainmeters. Noise at periods of a few days amounts to 50 nε. The two horizontal strainmeters show drift rates of up to 1 µε per month, and occasional false signals (evident from comparisons with the vacuum laser strainmeters) can accumulate occasionally to the order of 50 nε over times from hours to weeks. Results to date indicate that this technology on land could detect slow‐slip events of amplitude 100 nε and higher.

Initiation of Infrasonic Geosphere Waves Caused by Explosive Eruption of Hunga Tonga-Hunga Haʻapai Volcano

The paper presents the results of processing recordings of abnormal signals, which originated during the eruption of Hunga Tonga-Hunga Haʻapai volcano, and were registered by a laser nanobarograph and two laser strainmeters; there were three meters of sea-level variations, located in the Sea of Japan, and twelve meters of sea-level variations, located in the Pacific Ocean. Acoustic-gravity Lamb waves, generated in the atmosphere, caused disturbances of similar periods in the Earth’s crust, which were registered by laser strainmeters. Atmospheric impulse and Lamb waves during their propagation over the Pacific Ocean and the Sea of Japan initiated meteorological tsunamis in their waters, at periods corresponding to the seiches (Eigen oscillations) of registration stations’ location areas. In the records of all sea wave recorders, we did not find signs of a classical tsunami origination, and in the records of laser strainmeters, we did not find signals corresponding to seabed displacements at the point of the volcano explosion that led to the formation of a classical tsunami.

Registration of the hydroacoustic radiation sources by a system of spatially separated laser strainmeters

Registration of the hydroacoustic radiation sources by a system of spatially separated laser strainmeters

Deformation Anomalies Accompanying Tsunami Origination

Basing on the analysis of data on variations of deformations in the Earth’s crust, which were obtained with a laser strainmeter, we found that deformation anomalies (deformation jumps) occurred at the time of tsunami generation. Deformation jumps recorded by the laser strainmeter were apparently caused by bottom displacements, leading to tsunami formation. According to the data for the many recorded tsunamigenic earthquakes, we calculated the damping ratios of the identified deformation anomalies for three regions of the planet. We proved the obtained experimental results by applying the sine-Gordon equation, the one-kink and two-kink solutions of which allowed us to describe the observed deformation anomalies. We also formulated the direction of a theoretical deformation jump occurrence—a kink (bore)—during an underwater landslide causing a tsunami.

Cyclonic Process of the “Voice of the Sea” Microseism Generation and Its Remote Monitoring

The article presents the results of microseismic signals of the “voice of the sea” registration by a two-coordinate laser strainmeter during the passage of typhoons through and near the water area of the Sea of Japan. It was established that the “voice of the sea” microseisms appear and disappear almost simultaneously with primary microseisms, i.e., the powerful “voice of the sea” microseisms exist only in the presence of powerful wind waves, generated by a passing typhoon. According to the processing results of the obtained experimental data, the “voice of the sea” microseisms generation area is located in the “sea-land” transition zone, i.e., near and/or in the surf zone. Based on the data of the two-coordinate laser strainmeter, we determined the bearing of the “voice of the sea” microseisms generation area. The movement of this area coincides with the movement of the rear part of tropical cyclones.

Dynamics and Transformation of Sea Surface Gravity Waves at the Shelf of Decreasing Depth

This paper reviews the results of the processing of synchronized data on hydrosphere pressure variations and the Earth’s crust deformation in the microseismic range (5–15 s), obtained over the course of numerous experiments, using a coastal laser strainmeter and laser meters of hydrosphere pressure variations installed in various points of the Sea of Japan shelf. Interpreting the results, we have discovered new regularities in the dynamics of surface progressive gravity waves, and their transformation into primary microseisms, when waves move at the shelf of decreasing depth. For example, we found non-isochronous behavior of progressive waves, which manifests itself in a decrease in the periods of gravity waves due to the transformation of a part of their energy into the energy of primary microseisms. Furthermore, when processing the synchronous fragments of the records, made by laser strainmeters and laser meters of hydrosphere pressure variations, we identified approximate zones of the most effective transformation of the energy of gravity progressive waves into the energy of primary microseisms, which start from the depth of less than a half-wavelength and stretch to the surf zone.

Perturbation of the Earth’s rotation by monochromatic gravitational waves from astrophysical sources

Gravitational waves (GWs) of astrophysical origin were detected for the first time in 2015 through strain deformation measured at the Earth's surface. The inertia tensor of the deformable Earth is also disturbed resulting in the perturbation of its rotation vector and excitation of the rotational normal modes. Using a linearized theory of gravitation and the linearized equations of conservation of the angular momentum, we compute the equatorial polar motion and length of day changes generated by GWs. We show that GWs of strain amplitude ${h}_{0}$ and frequency ${f}_{g}$ give rise to perturbations of the inertia tensor of the Earth with an amplitude of ${10}^{14}{h}_{0}{f}_{g}^{2}$, resulting in relative perturbation of the Earth's rotation rate and equatorial polar motion respectively of the order ${10}^{6}{h}_{0}{f}_{g}^{2}$ and ${10}^{14}{h}_{0}{f}_{g}^{2}$. The amplitude of the rotational effect is much smaller than the geophysically induced rotational perturbation even if a resonance with the Earth's rotational normal modes would be possible. The amplitude of this rotational effect increases with the frequency but is several orders of magnitude below the theoretical sensitivity level of current geodetic instruments. The centrifugal deformation associated with the GW-induced polar motion would be $\ensuremath{\sim}{10}^{6}{f}_{g}^{2}{h}_{0}\ensuremath{\sim}{10}^{\ensuremath{-}17}/\sqrt{\mathrm{Hz}}$ for ${f}_{g}={10}^{\ensuremath{-}4}\text{ }\text{ }\mathrm{Hz}$ and ${h}_{0}={10}^{\ensuremath{-}16}$. The strain amplitudes of such centrifugal deformation are beyond the detectability of current laser strainmeters used to detect GWs. In the future, improvement in the sensitivities of geophysical instruments to measure Earth's rotation fluctuations, particularly at subdaily periods, and the development of the Laser Interferometer Space Antenna would make the present quantifications worth considering.