Borehole Tiltmeters Research Articles

Precise tilt measurement by seafloor borehole tiltmeters at the Nankai Trough subduction zone

In this study, geodetic and seismic phenomena occurring in the subduction zone were observed with two tiltmeters that were installed in seafloor boreholes drilled in the Kumano Basin in the Nankai Trough, southwest Japan. We used one electrolytic-type tiltmeter and one pendulum-type tiltmeter installed 6 and 19 m below the seafloor, respectively. The two tiltmeters have been continuously operated since 2019 and 2021, respectively. The records of the two tiltmeters showed microseisms, seismic signals of normal earthquakes, and variations that correlated well with the M2 tide (tidal response). The noise environment relative to existing seafloor observatories was assessed by comparing the power spectral densities of the tiltmeters and broadband seismometers in the seismic frequency band. The two tiltmeters and the seismometers showed similar spectral peaks in the microseism band, and at lower frequencies below 10–2 Hz, the pendulum tiltmeter had a noise level that was up to 20 dB lower than that of the broadband seismometers. The tidal responses of the tiltmeters were analyzed to reveal corresponding mechanisms because a large amplitude of the tidal response makes it difficult to detect geodetic phenomena. Considerable azimuthal dependence was observed in the NW–SE direction for both tiltmeters. The principal direction was approximately the same as the down-slope direction of the local bathymetry. This tendency was thus interpreted to be caused by the differences in the thickness of the sedimentary layer along the direction of the slope. Furthermore, the validity of the tilt measurements for the two tiltmeters was demonstrated by in-situ loading experiments, where the theoretical response of an elastic half-space medium was computed and compared with the experimental results. The results of the loading experiments can be explained using theoretical values with a set of realistic elastic moduli.Graphical

New Insights on Ground Deformation at Campi Flegrei Caldera Inferred From Kinematics and Dynamics Investigation of Borehole Tilt

AbstractThe study of the ground deformation in active calderas provides valuable indications of the ongoing dynamical processes. In this framework, we analyze the borehole tiltmeter data recorded at Campi Flegrei (Southern Italy) from their first installation (1 April 2015), in order to retrieve the kinematics of the ground deformation and its main anomalies. Our approach involves the nonlinear dynamics analysis aimed at the identification of the degrees of freedom of the system and thus its complexity. Starting from the second part of the year 2020, the behavior of the dynamical system becomes collective, and a locally significant deviation of the deformative pattern from the background trend is observed. In particular, a series of 15 slow tilt variations (like jumps lasting a few days) appears in the ground deformation. They are associated with a very low‐dimensional system likely generated by a local second‐order source. The latter is related to fluid migration and it is superimposed on the primary one located in Pozzuoli town and driving the current uplift of Campi Flegrei. The effects of such a local, second‐order stress field are, indeed, evident in the area of the volcanic dome of Mt. Olibano, where they are measured as tilt steps. The superposition of primary and second‐order sources of deformation acting contemporaneously can justify the recent variations in geophysical and geochemical parameters. Our approach based on the joint dynamical and kinematical analyses of the tiltmeter data can be applied to other volcanic/tectonic areas or extended to other geophysical and geochemical variables.

The 2018 phreatic eruption at Mt. Motoshirane of Kusatsu\u2013Shirane volcano, Japan: eruption and intrusion of hydrothermal fluid observed by a borehole tiltmeter network

We estimate the mass and energy budgets for the 2018 phreatic eruption of Mt. Motoshirane on Kusatsu–Shirane volcano, Japan, based on data obtained from a network of eight tiltmeters and weather radar echoes. The tilt records can be explained by a subvertical crack model. Small craters that were formed by previous eruptions are aligned WNW–ESE, which is consistent with the strike of the crack modeled in this study. The direction of maximum compressive stress in this region is horizontal and oriented WNW–ESE, allowing fluid to intrude from depth through a crack with this orientation. Based on the crack model, hypocenter distribution, and MT resistivity structure, we infer that fluid from a hydrothermal reservoir at a depth of 2 km below Kusatsu–Shirane volcano has repeatedly ascended through a pre-existing subvertical crack. The inflation and deflation volumes during the 2018 eruption are estimated to have been 5.1 × 105 and 3.6 × 105 m3, respectively, meaning that 1.5 × 105 m3 of expanded volume formed underground. The total heat associated with the expanded volume is estimated to have been ≥ 1014 J, similar to or exceeding the annual heat released from Yugama Crater Lake of Mt. Shirane and that from the largest eruption during the past 130 year. Although the ejecta mass of the 2018 phreatic eruption was small, the eruption at Mt. Motoshirane was not negligible in terms of the energy budget of Kusatsu–Shirane volcano. A water mass of 0.1–2.0 × 107 kg was discharged as a volcanic cloud, based on weather radar echoes, which is smaller than the mass associated with the deflation. We suggest that underground water acted as a buffer against the sudden intrusion of hydrothermal fluids, absorbing some of the fluid that ascended through the crack.

The M2 Tidal Tilt Results from USArray Seismic Data from the Western United States

ABSTRACTWe explore the detectability of M2 tidal tilt in the western part of the United States, using seismic velocity data from 40 stations in the EarthScope Transportable Array (TA) network. We augment these data with data from two additional stations both collocated at the Piñon Flats Observatory (PFO) in southern California (networks TA and Incorporated Research Institutions for Seismology [IRIS] International Deployment of Accelerometers [IDA]). We find a good agreement between the acceleration-tilt derived from the TA seismic data with the theoretical model (body Earth and ocean loading for M2). These results are also consistent with prior studies using borehole tiltmeters operated at PFO (Wyatt and Berger, 1980; Wyatt et al., 1982). We find statistically significant M2 tilt anomaly responses that correlate with large lateral variations in rock properties in Yellowstone National Park, which stem from volcanic sources in the region. We also examined deviations in the M2 tidal tilt mode in regions with other geological features including the Cascades volcanic range and a large plutonic body located in Idaho and eastern Oregon. Of these, only the Cascadia data show evidence of lateral variances of elastic properties, similar to that of the Yellowstone Caldera (YC). We conclude that tilt measurements from seismic noise data can successfully identify relatively large structural changes in elastic properties of the crustal Earth (e.g., the YC) and significant change in the elastic properties (e.g., Cascadia subduction zone). But, when the features are smaller and/or have a more muted variation in the elastic properties (e.g., the plutonic body in Idaho and eastern Oregon), the induced changes in the tilt values are too small to be detected using TA data.

Some Investigations on a Possible Relationship between Ground Deformation and Seismic Activity at Campi Flegrei and Ischia Volcanic Areas (Southern Italy)

In the present paper, we analyse ground tilt and seismicity at Campi Flegrei caldera and Ischia Island, two volcanic areas located in the south of Italy. These areas have been well studied for many years from a petrological, volcanological and geophysical view point. Moreover, due to the high seismic and volcanic risk for the populations living there, they are continuously monitored by networks of geophysical and geochemical sensors. We summarize the most important results that we obtained so far, concerning the observations of relationships between seismic activity and ground tilt anomalies, focusing on the time interval 2015–2018. First, we present a detailed description of the tiltmeter and seismic networks in both the investigated areas, as well as their development and improvement over time that has enabled high quality data collection. From the joint analysis of the seismic and borehole tiltmeter signals, we often notice concurrence between tilt pattern variations and the occurrence of seismicity. Moreover, the major tilt anomalies appear to be linked with the rate and energy of volcano-tectonic earthquakes, as well as with exogenous phenomena like solid Earth tides and hydrological cycles. The analysis that we present has potential applicability to other volcanic systems. Our findings show how the joint use tilt and seismic data can contribute to better understanding of the dynamics of volcanoes.

Relationship between river bank stability and hydrological processes using in situ measurement data

Many river banks throughout the world are prone to landslides; therefore, serious efforts are made to develop landslide early warning systems. This study presents a method by which the stability changes of the river banks can be continuously monitored; necessary measures can be taken in time to reduce the damage. The method was tested in Dunaszekcső (Hungary), where the high loess bank of the River Danube has been intensively moving since 2007. The tilts of the high bank were measured by two borehole tiltmeters. The connection between tilt values and the river- and groundwater-level variations was investigated by multivariable and moving window regression analyses on the basis of a 6-year-long observation from 2011 to 2016. The results show that increasing regression coefficients mean decreasing stability of the high river bank, so the developed method can be used for continuous supervision of the high bank stability. The method is also suitable for studying the causes of motion processes. Investigations showed clearly that the effect of groundwater table variations is two orders of magnitude higher than the water-level variations of the River Danube. In addition to the erosion of the river, various small tilts of the stable and unstable parts also contribute to the arising of new cracks in the stable part, decreasing its width.

Joint estimation of tiltmeter drift and volume variation during reservoir monitoring

Borehole tiltmeters are widely used to continuously record small surface deformation of reservoirs and volcanoes. Because these instruments display unknown long-term drift, only short-term tilt signal can be used for monitoring purpose. We propose a method to invert long-term time series of tilt data induced by strain variations at depth. The assumption that tiltmeter drift is linear over time is on its own insufficient to remove the drift and uniquely determine the deformation source parameters. To overcome this problem, we first invert the data with no constrain on the drift to obtain one particular solution among all admissible. Then, using the linearity of the forward model, we use the statistical properties of the drift distributions to restore the uniqueness of the solution. We illustrate our approach with four synthetic cases simulating volume changes of a reservoir. We demonstrate the efficiency of our method and show that the accuracy of estimated volume variation dramatically improves if low drift tiltmeters are used.

Detection of Earth's free oscillation excited by the Japan Mw9.0 Earthquake using different tiltmeter and strainmeter

The observatory network of the Crustal Deformation China Seismological Bureau was equipped with vertical pendulum tiltmeter, borehole tiltmeter, tunnel extension meters, multi-component borehole strainmeter, body strainmeter and other tilt and strain observation instruments. All of these instruments have recorded the Earth's free oscillation excited by the Japan Mw9.0 Earthquake. By analyzing those observations, all of the spheroidal oscillation modes (0S3—0S30) and toroidal oscillation modes (0T3—0T20) excited by the Japan Mw9.0 Earthquake were detected in this paper. In addition, comparing the different observation results which obtained by those instruments, we revealed their capacity to observe different kinds of oscillation and different frequency band modes, and analyzed report the reason. We found that the body strainmeter and the vertical pendulum tiltmeter have better observing results for spheroidal oscillation. Because of high noise in low frequency band, the borehole tiltmeter cannot observe the low-order spheroidal oscillation. In terms of observing the toroidal oscillation, the multi-component borehole strainmeter got a best result. The vertical pendulum tiltmeter observes a few toroidal oscillation modes, and the tunnel extension meters can only observe some low-order modes.

Results and analysis of earth tide observations with the borehole tiltmeter in Poltava

Results of harmonic analysis of eight years earth tides observations with the borehole tiltmeter of the Poltava Gravimetric Observatory are presented. Hight-precision parameters of the main tidal waves and Love´s numbers h and k which practically coincide with similar data from tiltmetric and gravimetric observations in 25 stations of Ukraine are received. The azimuthal inequality of a factor γ in the NS and EW directions isn't revealed. Resonant influence of the liquid core of Earth coincides with calculated theoretically.

The role of recent tectonics and hydrological processes in the evolution of recurring landslides on the Danube's high bank in Dunaföldvár, Hungary

There are high loess banks prone to landslide along the River Danube in Hungary. One of these is the high loess bank in Dunaföldvár, where several landslides occurred in the last decades. Quantitative relationships between the movements of the high loess bank and the variation of the water level of the River Danube, the ground water table, precipitation and temperature are investigated by two borehole tiltmeters and a vertical borehole extensometer. The twelve-year long observation from 2002 to 2014 made it possible to distinguish between the high bank movements due to slow recent tectonic and geomorphologic processes and the short-period (from hours to months) movements caused by hydrometeorological effects. The results revealed that besides geomorphologic processes recent tectonics can play an important role in the recurrence of landslides in the area. In the investigated period the total tilt of the high bank was 162μrad in the SSE direction according to the geomorphologic and recent tectonic processes in the surroundings of Dunaföldvár. Investigations of the relationships between the high bank movements and the water level of the River Danube, ground water table changes and the precipitation revealed that the tilt magnitudes caused by the ground water table variations are two orders of magnitude greater than the tilts caused by the water level regime of the river and the direct effect of the precipitation on the high bank tilts can be disregarded.

Observing slope stability changes on the basis of tilt and hydrologic measurements

Abstract In Hungary, the high loess bank of the River Danube in Dunaszekcső has been moving with varying rate since 2007. On the high bank a geodetic monitoring network was established in September 2007. At the same time two borehole tiltmeters and later two ground water level sensors were also installed. The high-sensitive tiltmeters made it possible to study the relationships between the small tilts of the high bank and the ground water levels and the water level of the River Danube. Results of the multiple regression analysis between tilt components and water levels showed that the temporal variation of the regression coefficients is in close connection with the stability of the high bank. The investigations also showed that the movements are in very strong connection with the variation of the ground water level and less depend on the variation of the water level of the River Danube. The characteristic tilt processes, 3–4 weeks before large movements, and the slope stability changes inferred from the relationships between tilts and water level variations can be useful for early warning of landslides.

Tilt signals at Mount Melbourne, Antarctica: evidence of a shallow volcanic source

Mount Melbourne (74°21′ S, 164°43′ E) is a quiescent volcano located in northern Victoria Land, Antarctica. Tilt signals have been recorded on Mount Melbourne since early 1989 by a permanent shallow borehole tiltmeter network comprising five stations. An overall picture of tilt, air and permafrost temperatures over 15 years of continuous recording data is reported. We focused our observations on long-term tilt trends that at the end of 1997 showed coherent changes at the three highest altitude stations, suggesting the presence of a ground deformation source whose effects are restricted to the summit area of Mount Melbourne. We inverted these data using a finite spherical body source, thereby obtaining a shallow deflation volume source located under the summit area. The ground deformation observed corroborates the hypothesis that the volcanic edifice of Mount Melbourne is active and should be monitored multidisciplinarily. Keywords: Tilt monitoring; volcanic dynamics; physics volcanology; ground deformation; Victoria Land. (Published: 1 June 2016) To access the supplementary material for this article, please see the supplementary files in the column to the right (under Article Tools). Citation: Polar Research 2016, 35 , 28269, http://dx.doi.org/10.3402/polar.v35.28269

Methods for monitoring land subsidence and earth fissures in the Western USA

Abstract. Depletion of groundwater resources in many deep alluvial basin aquifers in the Western USA is causing land subsidence, as it does in many regions worldwide. Land subsidence can severely and adversely impact infrastructure by changing the ground elevation, ground slope (grade) and through the development of ground cracks known as earth fissures that can erode into large gullies. Earth fissures have the potential to compromise the foundations of dams, levees, and other infrastructure and cause failure. Subsequent to an evaluation of the overall subsidence experienced in the vicinity of subsidence-impacted infrastructure, a detailed investigation to search for earth fissures, and design and/or mitigation of potentially effected infrastructure, a focused monitoring system should be designed and implemented. Its purpose is to provide data, and ultimately knowledge, to reduce the potential adverse impacts of land subsidence and earth fissure development to the pertinent infrastructure. This risk reduction is realized by quantifying the rate and distribution of ground deformation, and to detect ground rupture if it occurs, in the vicinity of the infrastructure. The authors have successfully designed and implemented monitoring systems capable of quantifying rates and distributions of ground subsidence and detection of ground rupture at multiple locations throughout the Western USA for several types of infrastructure including dams, levees, channels, basins, roadways, and mining facilities. Effective subsidence and earth fissure monitoring requires understanding and quantification of historic subsidence, estimation of potential future subsidence, delineation of the risk for earth fissures that could impact infrastructure, and motivation and resources to continue monitoring through time. A successful monitoring system provides the means to measure ground deformation, grade changes, displacement, and anticipate and assess the potential for earth fissuring. Employing multiple methods, a monitoring strategy utilizes an integrated approach, including both regional and local measurements. Various methods implemented include conventional practices and proven, instrumented in-ground sensing systems. The conventional techniques include repeat optical levelling and global positioning system (GPS) surveys, ground reconnaissance, photo-geological analysis, groundwater monitoring, and tape-extensometers. Advanced techniques include the processing and interpretation of differential interferograms of repeat-pass, satellite-based synthetic aperture radar data (InSAR), borehole tiltmeters, microseismic arrays, excavation of monitoring trenches, and time-domain reflectometry (TDR).

A simple pendulum borehole tiltmeter based on a triaxial optical-fibre displacement sensor

Sensitive instruments like strainmeters and tiltmeters are necessary for measuring slowly varying low amplitude Earth deformations. Nonetheless, laser and fibre interferometers are particularly suitable for interrogating such instruments due to their extreme precision and accuracy. In this paper, a practical design of a simple pendulum borehole tiltmeter based on laser fibre interferometric displacement sensors is presented. A prototype instrument has been constructed using welded borosilicate with a pendulum length of 0.85 m resulting in a main resonance frequency of 0.6 Hz. By implementing three coplanar extrinsic fibre Fabry-Perot in-terferometric probes and appropriate signal filtering, our instrument provides tilt measurements that are insensitive to parasitic deformations caused by temperature and pressure variations. This prototype has been installed in an underground facility (Rustrel, France) where results show accurate measurements of Earth strains derived from Earth and ocean tides, local hydro-logic effects, as well as local and remote earthquakes. The large dynamic range and the high sensitivity of this tiltmeter render it an invaluable tool for numerous geophysical applications such as transient fault motion, volcanic strain and reservoir monitoring.

A new capacitive borehole tiltmeter for crustal deformation measurement and its performance analysis

Borehole inclinometers are important observation instruments used to measure ground tilt movement and monitor crustal deformation of solid tides and geological landslide disasters. They are widely used in oil exploration, mineral resource drilling, well logging, exploration and other fields. There is potential for development of rock stress strain monitoring tools. Many types of tiltmeters have been installed, such as SQ-7, FSQ, VS and JB. However, these tiltmeters are generally installed in a deep cave to avoid the interference of temperature, humidity, and human activities. With the urbanization of human society, suitable installation locations are difficult to find. To solve the problem, a two-component borehole tiltmeter, named the CBT-type tiltmeter, is proposed in this paper. It can be installed in a borehole less than 500m deep to eliminate environmental influences. The tiltmeter is composed of two sophisticated gravitational swing and two capacitive transducers. From preliminary theory and experiment analysis, its linear correlation coefficient is higher than 0.99, its co-seismic response is rapid and its noise level is up to 10−4 arc seconds in practice.

Investigation of Dynamic and Kinematic Landslide Processes by Borehole Tiltmeters and Extensometers

Landslides cause many damages both in properties and in human life. The high loess banks along the River Danube are the most susceptible areas to mass movements in Hungary. Two test sites, one in Dunaföldvár and the other in Dunaszekcső, were chosen for the investigation of the kinematic and dynamic processes of the high loess banks due to tectonic, hydrologic and environmental effects. On both test sites, more landslides occurred in the last century. In Dunaszekcső the latest landslide took place in 2008. Here a new landslide has been developing since 2010. In Dunaföldvár borehole tilt and borehole extensometric measurements have been carried out since 2002. In Dunaszekcső the borehole measurements began in the autumn of 2007, thus both the large landslide formed in 2008 and the newly developing landslide could be observed. Comparison of tilt data with ground water level changes and the stage of the River Danube resulted in new knowledge of the landslide development processes of the high loess banks. The measurements made evident that the ground water level changes have two-three orders of magnitude larger effect on the high bank stability than the water level variations of the River Danube. The characteristic tilt processes during a 3-4 weeks period before the slump can be used for early warning of landslides. The increasing tilt amplitudes and regression coefficients between tilt and ground water levels could be the precursor of a forthcoming landslide.

Deformation Monitoring and Prediction of a Reservoir Landslide in Sichuan Province, China

Hydropower reservoirs change the local geo-environment greatly and often induce reservoir bank landslides. Hongyanzi landslide is a large rejuvenated ancient landslide in Pubugou Hydropower Station reservoir area in western China Sichuan Province. To study the deformation of the Hongyanzi landslide, we arranged multi-parameter monitoring using GPS, fixed borehole tilt-meter, osmometer, and crack-meter and collected continuous data of displacement and ground water table. The monitoring data, together with the reservoir water level data, show that the landslide deforms obviously during reservoir water level is falling, while it deforms little in the other period. Comprehensive analysis of the deformation and reservoir water level implies that the seepage force caused by water level difference between the inner and outer slope may be the key factor. Through regression analysis, the authors established a forecast model for landslide deformation based on ground water table and reservoir water level; thus concluded that reducing the falling velocity of reservoir water level may slow the landslide deformation down.

Recurrent landsliding of a high bank at Dunaszekcső, Hungary: Geodetic deformation monitoring and finite element modeling

Five years of geodetic monitoring data at Dunaszekcső, Hungary, are processed to evaluate recurrent landsliding, which is a characteristic geomorphological process affecting the high banks of the Middle Danube valley in Hungary. The integrated geodetic observations provide accurate three dimensional coordinate time series, and these data are used to calculate the kinematic features of point movements and the rigid body behavior of point blocks. Additional datasets include borehole tiltmeter data and hydrological recordings of the Danube and soil water wells. These data, together with two dimensional final element analyses, are utilized to gain a better understanding of the physical, soil mechanical background and stability features of the high bank. Here we indicate that the main trigger of movements is changing groundwater levels, whose effect is an order of magnitude higher than that of river water level changes. Varying displacement rates of the sliding blocks are interpreted as having been caused by basal pore water pressure changes originating from shear zone volume changes, floods of the River Danube through later seepage and rain infiltration. Both data and modeling point to the complex nature of bank sliding at Dunaszekcső. Some features imply that the movements are rotational, some reveal slumping. By contrast, all available observational and modeling data point to the retrogressive development of the high bank at Dunaszekcső. Regarding mitigation, the detailed analysis of three basic parameters (the direction of displacement vectors, tilting, and the acceleration component of the kinematic function) is suggested because these parameters indicate the zone where the largest lateral displacements can be expected and point to the advent of the rapid landsliding phase that affects high banks along the River Danube.

Reply to comment by D. Carbone and D. Patanè on “Multidisciplinary investigation on a lava fountain preceding a flank eruption: The 10 May 2008 Etna case”

Reply to comment by D. Carbone and D. Patanè on “Multidisciplinary investigation on a lava fountain preceding a flank eruption: The 10 May 2008 Etna case”

The role of vegetation in the daily and yearly small tilt variations of the Danube's high bank, Hungary

In this paper relationships between vital processes of plants and small movements of a river bank slope are investigated. For monitoring the movements, two geodetic test sites were established on the high loess bank of the river Danube at Dunafoldvar and Dunaszekcső in Hungary. At both sites two highly sensitive borehole tiltmeters were installed for continuous monitoring of movements. The recorded daily tilt amplitudes were compared with the precipitation and the potential evapotranspiration of the area. It was pointed out that the daily tilt amplitudes are in close connection with the vital processes of the plants. The precipitation effect on the seasonal variations of the tilt amplitudes is of minor importance which means that the vegetation has a much more important role in the water balance of the upper soil layer than the precipitation. Our investigation showed that the vegetation can be effective in hindering landslides occurrence since the infiltration of the precipitation into the deep soil layers and so the moistening of the high bank can be significantly diminished by planting appropriate vegetation on slopes.