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Tiltmeters have the potential to resolve ground deformation due to changes in hydraulic head induced by conduit pressurization. Conduit pressure variations cause groundwater to be stored or released from storage within the surrounding rock matrix. We modeled this process and infer whether the resulting deformation is measurable with tiltmeters and what behavior to expect by fully coupling porous media flow and solid mechanics in a poroelastic, 2D finite element model. Parameter sets globally representative of Paleozoic, Mesozoic, and Cenozoic confined and unconfined aquifers are considered. Our analysis focuses on the impact of the parameterization on pore pressure, vertical displacement, and tilt. We find that the spatial distribution of the poroelastic signal depends on the hydraulic diffusivity, and its magnitude depends on the mechanical and coupling parameters. Additional analysis of the impacts of conduit radius and depth suggests that tilt polarity could be an indicator of conduit location and relative conduit size. We calibrated the model to data observations acquired at the Santa Fe River Sink‐Rise system in north‐central Florida, US. We find that an overlying clay‐rich layer may act to partially confine the aquifer. Although the observed tilt signal is present in radial and transverse components and polarity reversals occur, we were able to recover the magnitude and general trend of the tilt response. Plain Language Summary: Our study focused on understanding how changes in ground deformation can be caused by groundwater flow induced by a pressurized karst conduit. We modeled this process in different types of aquifers to determine if the deformation can be measured using tiltmeters, instruments that measure changes in the angle of the ground. We also explored the effect of conduit size and depth. Our findings show that the distribution and magnitude of the ground response depend on the physical parameters of the aquifer. Additionally, we find that tilt data can provide information about conduit location, size, and depth. We tested the model using data from the Santa Fe River Sink‐Rise system in Florida. We find this system may behave as a partially confined aquifer due to the presence of clay in the overlying unit. From the use of our simplified numerical formulation, we were able to recover the magnitude and overall trend of the observed tilt data. Key Points: Poroelastic response is governed by an interconnection between aquifer hydraulic diffusivity, Biot‐Willis coefficient, and elastic moduliSmall tilt arrays can potentially provide information on relative conduit location and sizeHeterogeneity, complex geometry, and non‐uniqueness present challenges in progressing from synthetic simulations to real‐world predictions [ABSTRACT FROM AUTHOR]

The detection of preslip, occurring hours to days before a large earthquake, using geodetic measurements has been a major focus in earthquake prediction research. A recent study claims to have detected a preseismic signal interpreted as accelerating slip near the hypocenter of the 2011 great Tohoku‐oki earthquake, starting approximately 2 hr before the mainshock. This claim is based on a stacking procedure using GNSS (Global Navigation Satellite System) data. However, a follow‐up study demonstrated that the signal disappeared when specific GNSS noise was corrected. Here we utilize tiltmeter records, independent on GNSS, to check whether the claimed preseismic signal is detected using a similar stacking procedure. Our results show no acceleration‐like deformation from 2 hr before the mainshock. This indicates that no precursory slip exceeded the noise level of the tilt data, and if any preslip occurred, it was less than 5.0 × 1018 Nm in seismic moment. Plain Language Summary: The ability to detect large earthquakes before they occur would be invaluable for mitigating damage. Researchers have been searching for precursory signals in crustal deformation data, believing that if precursory slip (fault movement before a major earthquake) is large enough, it could be detected by GNSS or tiltmeters, enabling earthquake prediction. The 2011 Tohoku‐oki earthquake provided a valuable opportunity to study this phenomenon. Extensive data was collected, but previous studies found no significant pre‐earthquake signals on timescales of hours to days. A recent GNSS study claimed an acceleration‐like change 2 hr before the main shock, but another study using the same data disputed this. While reanalysis using the same GNSS data is important, it is also susceptible to the influence of the same noise sources. To avoid this, this study analyzed tiltmeter data, finding no evidence for the precursory deformation suggested earlier. This result indicates no significant precursory slip before the Tohoku‐oki earthquake that causes deformation larger than a noise level of the tiltmeter data. This result can provide constraints on the magnitude of the precursory slip immediately before the mainshock. Key Points: Tiltmeter records are used to determine whether a preseismic signal of the 2011 great Tohoku‐oki earthquake is detectedNo acceleration‐like tilt deformation from about 2 hr before the mainshock is recordedAn upper bound on the size of the preslip immediately before the mainshock can be estimated from the noise level of the observation data [ABSTRACT FROM AUTHOR]

The engineering behavior of rock masses is controlled more by the strength of the discontinuity surfaces than by the strength of the intact rock. Asperity angles play a very important role in the shear strength of discontinuity surfaces. The strength of discontinuity surfaces can be determined by direct shear tests in the laboratory. However, it is not always possible to obtain suitable discontinuity surfaces from natural discontinuities in the field and place them in the shear test device. In this study, in addition to direct shear tests on 9 different rocks, basic friction angles (φb ) were determined with a tiltmeter device and the second degree asperity angles (i) on the discontinuity surfaces were determined with an electromechanical profilometer device. From these two values, the total friction angles were obtained (φ1 = φb + i). These values were compared with the results of φb andφ1 obtained from Patton’s bilinear failure envelope by direct shear tests under different normal stresses and their compatibility was evaluated. It was determined that the failure envelopes obtained from direct shear tests performed at different normal stress levels comply with the Patton bi-linear failure model for all 9 specimens. According to the results obtained, when the basic friction angles and total friction angles obtained from direct shear tests were compared with the values obtained from profilometer and tiltmeter tests; it was determined that the basic friction angles were in a very high level of agreement for all 9 rocks tested (R² = 0.91). Total friction angles can be obtained with high accuracy except for two rocks (granodiorite and marble) with high strength (R² = 0.86). It was concluded that basic friction angles and total friction angles can also be obtained by profilometer and tiltmeter tests whenever it is not possible to direct shear tests. [ABSTRACT FROM AUTHOR]

Abstract Etna is a highly active volcano with frequent eruptions and is closely observed with different monitoring techniques. One of the monitoring methods is a network of short-base tiltmeters that provides continuous control of ground deformation. Since 1996, this network has been integrated with a long-base fluid tiltmeter installed in two 80 m long connected tunnels at the high-altitude (2850 m a.s.l.) volcanological observatory of Pizzi Deneri (PDN) located on the volcano’s summit. The instrumentation was devised with an innovative configuration composed of mercury, free to move along the entire length of the tiltmeter in response to the ground tilt, and laser sensors to measure the changes in the mercury levels. In this study, for the first time, we present the entire 25-year series of data recorded by this instrumentation. During this long interval, the Etna volcano was characterized by numerous major eruptions due to dyke intrusions. The tilt variations recorded in the short-term during the rapid intrusive phases are presented and discussed. These signals contributed both to the modeling of eruptive processes, and in particular in the case of the 2002–2003 eruption, to the real-time understanding of the ongoing eruptive phenomenon, supporting the correct hazard assessment. In the medium-long term (years to decades), we show and discuss that the PDN signal is mainly related to the marked sliding of the entire eastern sector of the volcano. Graphical Abstract

Etna is a highly active volcano with frequent eruptions and is closely observed with different monitoring techniques. One of the monitoring methods is a network of short-base tiltmeters that provides continuous control of ground deformation. Since 1996, this network has been integrated with a long-base fluid tiltmeter installed in two 80 m long connected tunnels at the high-altitude (2850 m a.s.l.) volcanological observatory of Pizzi Deneri (PDN) located on the volcano's summit. The instrumentation was devised with an innovative configuration composed of mercury, free to move along the entire length of the tiltmeter in response to the ground tilt, and laser sensors to measure the changes in the mercury levels. In this study, for the first time, we present the entire 25-year series of data recorded by this instrumentation. During this long interval, the Etna volcano was characterized by numerous major eruptions due to dyke intrusions. The tilt variations recorded in the short-term during the rapid intrusive phases are presented and discussed. These signals contributed both to the modeling of eruptive processes, and in particular in the case of the 2002–2003 eruption, to the real-time understanding of the ongoing eruptive phenomenon, supporting the correct hazard assessment. In the medium-long term (years to decades), we show and discuss that the PDN signal is mainly related to the marked sliding of the entire eastern sector of the volcano. [ABSTRACT FROM AUTHOR]

Abstract The detection of preslip, occurring hours to days before a large earthquake, using geodetic measurements has been a major focus in earthquake prediction research. A recent study claims to have detected a preseismic signal interpreted as accelerating slip near the hypocenter of the 2011 great Tohoku‐oki earthquake, starting approximately 2 hr before the mainshock. This claim is based on a stacking procedure using GNSS (Global Navigation Satellite System) data. However, a follow‐up study demonstrated that the signal disappeared when specific GNSS noise was corrected. Here we utilize tiltmeter records, independent on GNSS, to check whether the claimed preseismic signal is detected using a similar stacking procedure. Our results show no acceleration‐like deformation from 2 hr before the mainshock. This indicates that no precursory slip exceeded the noise level of the tilt data, and if any preslip occurred, it was less than 5.0 × 1018 Nm in seismic moment.

На полуострове Камчатка в 2019 г. были возобновлены наблюдения за наклонами земной поверхности. Целью наблюдений является получение дополнительной информации о медленных движениях земной поверхности, обусловленных различными геодинамическими явлениями. В первую очередь, это относится к изучению связи деформации с региональной сейсмичностью, а также с подготовкой и динамикой вулканических извержений. Помимо изучения медленных движений, сеть наклономерных станций может использоваться для исследования земных приливов. Перечисленные выше задачи могут быть решены лишь при наличии соответствующих средств сбора, обработки и хранения получаемой информации. Основной технической сложностью при создании аппаратурно-программного комплекса (АПК), являлась разнотипность имеющегося в наличии оборудования. В работе приводится описание программных и технических решений, использованных при реорганизации сети наклономерных наблюдений. В качестве примера работы комплекса приводятся результаты ретроспективного анализа данных, позволяющие предполагать наличие отклика в наклономерных данных на Земные приливы. Основное направление дальнейшего развития АПК — создание дополнительных программных модулей обработки, которые могут быть выборочно использованы в зависимости от поставленной задачи. Кроме того, ведется работа по предоставлению пользовательского доступа в исследовательских целях к накопленному архиву данных.

Triggering intrusions of phreatic eruptions are often observed as seismic and ground deformation signals on a time scale of minutes. The current understanding of hydrothermal intrusions still needs improvement to obtain insight into the eruption scale from the observables. We examine local geophysical data from the precursory hydrothermal intrusion of the 2018 phreatic eruption of Kusatsu‐Shirane volcano. To achieve an integrated intrusion model, we divide analyzing time window into the onset, middle, and climax. Focusing on the transient response of tilt data for the sudden pressurization, we estimate a vertical tensile opening (1.7 × 103 m3/s in 40 s) at 1.1 km depth for the intrusion onset. Pressurization can represent the start of vapourization. Very long period (VLP, 0.033–0.1 Hz) seismic signals are adopted to constrain the middle and climax phases. We obtained two sequential semi‐horizontal tensile crack oscillation sources with peak volume changes of 3.6 × 104–1.9 × 105 m3 at 0.3–0.6 km depths. The second VLP source acted as a final trigger of the eruption to cause depressurization in the shallow portion of the intruded region, which is constrained as having reached 0.1 km depth by surface deformation. Simultaneously, we find another depressurization originated from depth in the climax due to a decrease in the hydrothermal intrusion rate. Through comparison with the 2014 Ontake phreatic eruption, the total inflation volume may correlate with eruption scales. Intruded hydrothermal fluid and local structure characteristics also may have to be considered to evaluate the eruptions scales from inferred signal source intensity. Plain Language Summary: Phreatic eruptions, emitting non‐fresh magma fragments, are driven by underground water and gas mixtures intruding into the subsurface. Local geophysical observations often detect intrusions as seismic and ground deformation signals. Those observation data potentially provide insight into eruption and hazard scale evaluations. However, such an interpretation is still challenging for the current understanding. This paper examines seismic and ground deformation data associated with the precursory intrusion of a phreatic eruption at Kusatsu‐Shirane volcano in Japan, revealing a detailed hydrothermal intrusion process. Using ground deformation data, we have found that an aqueous intrusion started at 1.1 km depth. This starting process may represent the vapourization onset of underground water and gas mixtures. By analyzing seismic signals having a longer dominant period (>10 s), we revealed the intrusion path from the starting region to beneath the 2018 eruption vent and the final triggering for the eruption. Through comparisons with other phreatic eruptions, we find that the total deformation volume may correlate with the eruption intensity scales such as the mass emitted volcanic ash and the maximum eruption cloud height. However, there is still room for considering hydrothermal fluid characteristics and local structures to evaluate the eruption scale properly from observed data. Key Points: A sudden hydrothermal intrusion onset is constrained by adopting transient tiltmeter responsesVery long period band seismic signals reflect the hydrothermal intrusion behaviors during the middle and climax phasesTilt and seismic records show precursory depressurization in shallow depth as the final eruption trigger [ABSTRACT FROM AUTHOR]

This paper presents a high-precision component-type vertical pendulum tiltmeter based on an FPGA (Field Programmable Gate Array) that improves the utility and reliability of geophysical field tilt observation instruments. The system is designed for rapid deployment and offers flexible and efficient adaptability. It comprises a pendulum body, a triangular platform, a locking motor and sealing cover, a ratiometric measurement bridge, a high-speed ADC, and an FPGA embedded system. The pendulum body is a plumb-bob-type single-suspension wire vertical pendulum capable of measuring ground tilt in two orthogonal directions simultaneously. It is installed on a triangular platform, sealed as a whole, and equipped with a locking motor to withstand a free-fall impact of 2 m. The system utilizes a differential capacitance ratio bridge in the measurement circuit, replacing analog circuits with high-speed AD sampling and FPGA digital signal processing technology. This approach reduces hardware expenses and interferences from active devices. The system also features online compilation functionality for flexible measurement parameter settings, high reliability, ease of use, and rapid deployment without the need for professional technical personnel. The proposed tiltmeter holds significant importance for further research in geophysics.

We have developed a novel radiopaque tiltmeter (ROT) that can indicate patient tilt during a radiography examination and display it on X-ray images. This study evaluated the effect of variation of patient tilt on the reproducibility of Fowler's position for chest radiography and the accuracy of the ROT. We evaluated the reproducibility of Fowler's position based on changes from the first day in the central venous catheter (CVC) tip position and the cardiothoracic ratio (CTR) with and without a digital tiltmeter to verify its efficacy in patients who underwent mobile chest radiography. The ROT contains radiopaque liquid consisting of white barium sulfate solution and oil and has a scale bar of 15°–75° with increments of 15° to indicate ROT tilt. The ROT tilt was increased from 10° to 80° in increments of 10°. We then evaluated (1) the difference between the ROT tilt and the tilt measured with a digital tiltmeter, and (2) the ROT tilt displayed on the X-ray image. With regard to reproducibility in Fowler's position, changes in the CVC tip position were 2.8 ± 3.9 mm and 10.7 ± 10.6 mm with and without the tiltmeter, respectively (p < 0.05) and the respective rates of change in the CTR were 0.7% ± 0.6% and 4.0% ± 2.1% (p < 0.05). Differences between the ROT tilt and the tilt measured by the digital tiltmeter were within ±2.5°. All ROT tilts displayed on the X-ray images were recognized exactly as each tilt. Our novel ROT had the potential to accurately indicate patient tilt during chest radiography, which could be helpful in terms of reproducibility and precise follow-up. Use of the ROT for determination of patient tilt can improve reproducibility in Fowler's position, allowing more accurate serial X-ray imaging. [ABSTRACT FROM AUTHOR]

A novel instantaneous tiltmeter with dynamic and static monitoring functions is reported that is based on liquid metal dynamic wetting behavior in a bio-fabricated anisotropic microchannel. The proposed system achieves instantaneous tiltmeter functionality, offering a broad detection range (-90°-90°) with high precision (0.05°), a rapid reaction time (0.11 s), and enhanced durability. Moreover, a seamless integration has enabled water wave detection, language programming, and human limb monitoring. Especially, the integration of tiltmeter and a t3D motion platform results in a surface structure scanning system capable of effectively performing large area (>200 cm 2 ) and height difference scanning functions. This innovative approach holds great potential for transformative changes in the fields of advanced manufacturing, flexible robotics, and the flexible sensing, further facilitating widespread adoption., (© 2024 Wiley‐VCH GmbH.)

Abstract 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 main structure of the Baishihu suspension bridge was connected to the anchor foundations by three main steel cables. The wooden pedestrian deck was fixed to the main steel cables using steel beams and was stabilized by two stabilizing cables. The stabilizing cables and bridge body were joined by 44 steel connecting rods. Therefore, the slope stability at the anchorage foundations of the main steel cables, as well as the performance monitoring and analysis of the main steel cables and stabilizing cables, are critical to the overall performance of the suspension bridge. This paper discusses the performance monitoring and analysis of the steel cable deflection and cable strength for this bridge, as well as the main considerations and results of the stability analysis of the bridge abutments and side slopes of the two banks. Water-level observation wells, inclinometers, and tiltmeters monitoring were used to record reference data for the analysis of the slope stability performance. Additionally, the three-dimensional dynamic analysis program VFIFE was used to analyze the deformation and motion of the bridge. The final steady-state results were used to compare the static design value and monitoring data. The dynamic response before the final steady state was also observed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We analyzed the data recorded by the NE-Italy subsurface tilt and strainmeter network evidencing a coherent transient signal in the recordings of four tiltmeter sites in the 1984–1990 period that produced a tilt along the main fractures. Borrowing from classical seismology techniques, we used the uprise times to locate the transient signal source. The propagation velocity is compatible with a fluid diffusion process that starts from a source located close to the hypocenter of the February 10, 1983 Uccea earthquake, MD = 4.2 at the Italy-Slovenia border, at an estimated depth of 10.8 km. Our results add to the previous interpretation of a transient signal recorded by several global navigation satellite system (GNSS) stations in the 2006–2009 period in terms of fluid diffusion below the Bovec basin (Slovenia). That source was located upon continuation to the northwest of the Ravne fault, few kilometers to the northeast from the present one, and about 6 km from the July 12, 2004 Bovec–Krn earthquake, Mw = 5.1, depth ~6.1 km. These observations suggest that the area is subject to fault valve behavior episodes that released fluids trapped at depth to the surrounding region as pore-pressure bulges. The convergence between Alpine and External Dinarides structures in this area puts highly permeable dolomitic limestones in contact with low-permeable fine-grained limestones and flysch formations. Therefore, the conditions for overpressure generation can be created, whereas fault movements, from time to time, in close relation with seismic events, can enable fluid diffusion in the surroundings. We also estimated the possible fluid influx needed to maintain overpressure and possible discharge across both the faults. The study provides insights on pore–fluid pressure variations related to slow slip events from a context different from subduction or transform margins, i.e., in a continental collision area.

The paper presents the results of tiltmeter observations on the Kamchatka Peninsula in 2012–2016. Of the six tiltmeter stations operating in this period, two were successful, located in the area of the Klyuchevskaya volcano group, where tiltmeters were installed taking into account the technical requirements. During the period under consideration, two significant geodynamic events occurred on the Kamchatka Peninsula: the Sea of Okhotsk earthquake with MW = 8.3 and a source depth of 630 km; the Tolbachik Fissure eruption, named after the 50th anniversary of the Institute of Volcanology (TFE-50). The simultaneous occurrence of an anomaly, which can be regarded as a precursor, in the behavior of the tilts at two points, as well as activation of a remote foreshock in Avacha Bay, indicate a single geodynamic process on a regional scale preceding the Sea of Okhotsk earthquake. At the point closest to the TFE-50 eruption (distance about 40 km), the N–S component shows a well-pronounced anomaly that began 5 months prior to the eruption, with a positive tilt of ~70 µrad. This indicates the complex geodynamic processes occurring before the TFE-50 eruption, caused by magma migration in layers with neutral buoyancy according to the geophysical model of the magma feeder system of the Klyuchevskaya volcano group. The obtained tilt data indicate that they can be a very significant supplement to the modern method of observing movements of the Earth's surface using GPS technology. [ABSTRACT FROM AUTHOR]

Structural Health Monitoring System (SHMS) works as an efficient platform for monitoring health condition and and deterioration of civil structures during long-term service periods. One of the sensors is currently applied to Soekarno Bridge is tiltmeter. Vertical displacement data are often required to reflect the overall response of bridge span, however the Soekarno Bridge does not have any displacement sensor. On the other hand, the displacement sensor is very costly compared to tiltmeter. A method is proposed to estimate bridge displacement using data that is collected through tiltmeter. The method is using interpolation and numerical integration to evaluate the displacement. The result shows that the result obtained from the proposed method is reliable with accuracy of displacement around 5 mm. Some recommendations for further implementation of the sensors are provided.

A residual tilt after a teleseismic earthquake is described in this work. The results of static and dynamic modeling of this event fit the measured values. The conditions that make observations of residual deformations of teleseismic events possible and the prospects for using the tiltmeter network for monitoring seismically active regions are discussed. [ABSTRACT FROM AUTHOR]

Abstract Recent developments of ocean‐bottom pressure gauges (PG) have enabled us to observe various waves including seismic and tsunami waves covering periods of T ∼ 100–103 s. To investigate the quality for broadband observation, this study examined the broadband PG records (sampling rate of 1 Hz) around Japan associated with the 2010 Chile earthquake. We identified three distinct wave trains, attributed to seismic body waves, Rayleigh waves, and tsunamis. Clear dispersive features in the Rayleigh waves and tsunamis were explained by theories of elastic waves and gravity waves. Quantitative comparison between pressure change and nearby seismograms demonstrated the validity of the theoretical relation between pressure p and vertical acceleration az for ∼3 hr from the origin time. We also found a relationship between p and vertical velocity vz holds only at the first P wave arrival, but not for later arrivals. Similar results were confirmed for various earthquakes with different source‐station distances and magnitudes, suggesting the robustness of these relations. The results demonstrate that the high‐sampling rate (≥1 Hz) is necessary to observe seismic‐wave dispersion and PG can record both seismic waves and tsunamis with reasonable quality for waveform analyses, whereas conventional onshore and offshore seismometers or tide gauges can observe either of seismic waves and tsunamis. Utilizing the high‐sampling PG in combination with the seismic and tsunami propagation theory for estimating earthquake source process or analyzing wave propagation processes in the ocean will deepen our geophysical understanding of the solid‐fluid coupled system in the Earth and contribute toward disaster mitigation.

Recent developments of ocean‐bottom pressure gauges (PG) have enabled us to observe various waves including seismic and tsunami waves covering periods of T ∼ 100–103 s. To investigate the quality for broadband observation, this study examined the broadband PG records (sampling rate of 1 Hz) around Japan associated with the 2010 Chile earthquake. We identified three distinct wave trains, attributed to seismic body waves, Rayleigh waves, and tsunamis. Clear dispersive features in the Rayleigh waves and tsunamis were explained by theories of elastic waves and gravity waves. Quantitative comparison between pressure change and nearby seismograms demonstrated the validity of the theoretical relation between pressure p and vertical acceleration az for ∼3 hr from the origin time. We also found a relationship between p and vertical velocity vz holds only at the first P wave arrival, but not for later arrivals. Similar results were confirmed for various earthquakes with different source‐station distances and magnitudes, suggesting the robustness of these relations. The results demonstrate that the high‐sampling rate (≥1 Hz) is necessary to observe seismic‐wave dispersion and PG can record both seismic waves and tsunamis with reasonable quality for waveform analyses, whereas conventional onshore and offshore seismometers or tide gauges can observe either of seismic waves and tsunamis. Utilizing the high‐sampling PG in combination with the seismic and tsunami propagation theory for estimating earthquake source process or analyzing wave propagation processes in the ocean will deepen our geophysical understanding of the solid‐fluid coupled system in the Earth and contribute toward disaster mitigation. Plain Language Summary: Recent developments of offshore ocean‐bottom observation networks have enabled us to use high‐sampling (one or more samples per second) seafloor pressure gauge (PG) data. This study investigated PG records with broadband period range (seconds to hours) around Japan during the 2010 Chile earthquake. We identified a seismic P wave train arriving ∼20–30 min after the focal time. Another seismic wave train due to the surface Rayleigh wave during ∼70–110 min and tsunamis during ∼24–72 hr was also confirmed, which showed a dispersive feature; long‐period waves arrive earlier than short‐period waves. The dispersion theories obtained from the elastic and fluid dynamics thoroughly explained these features. We also compared wave amplitudes between the PG and nearby ocean‐bottom seismometer and confirmed the validity of the relationship between pressure and vertical acceleration and between pressure and vertical velocity. This study demonstrates PG can record both seismic and tsunami signals clearly with reasonable quality, while conventional seismometers or tide gauges can either. Ultrabroadband observation of PG plays an important role in deepening our understanding of geophysical wave propagation processes in the solid‐fluid coupled system in the ocean and enables delivery of essential information for earthquake early warning and disaster mitigation. Key Points: High‐sampling rate is important for pressure gauges to record seismic body waves, Rayleigh waves, and tsunamis and their dispersive featureTheoretical relation between pressure and vertical acceleration (p = ρwΗ0az) is valid for a long time (∼3 hr for the 2010 Chile earthquake)A relationship between pressure and vertical velocity (p = ρwc¯0vz) holds only at the first P wave arrival, but not for later phases [ABSTRACT FROM AUTHOR]

In the southwest Japan subduction zone, short‐term slow slip events (SSEs) accompanying nonvolcanic tremor (ETS: episodic tremor and slip) occur repeatedly with recurrence intervals of several months. It is important to know the detailed slip areas of the SSEs because short‐term SSEs occur at the downdip extension of a megathrust earthquake rupture zone, and hence, the SSEs play a key role in the stress buildup processes of the megathrust earthquakes. Although most of the previous studies model a SSE fault motion with uniform slip on a rectangular fault, this may lead to a bias in estimating the slip area. In this study we estimate a spatial slip distribution for each of the short‐term SSEs from tilt offset measurements. In total, the slip distributions of 61 SSEs in Shikoku from January 2001 to March 2019 are obtained. The ETS zone in Shikoku is divided into three segments in terms of slip history of the SSEs. Before 2011, the slip areas of most of the SSEs are limited in any one of the three segments. After 2012, however, the number of SSEs having a slip area that extends to multiple segments increases. The slip histories at each position in the ETS zone suggest that the short‐term SSE activity is affected by the occurrence of nearby long‐term SSEs. The average slip rate over 18 years suggests that an estimated slip deficit in the ETS zone in western Shikoku could be released by long‐term SSEs, or coseismic slip or afterslip of the megathrust earthquakes. Key Points: The slip distributions of 61 short‐term slow slip events (SSEs) from 2001 to 2019 in Shikoku, Japan, are estimated from tilt offset dataThe estimated slip history of the SSEs shows that the SSE zone is divided into three segmentsThe number of short‐term SSEs with larger slip extent and seismic moment increases after 2012 [ABSTRACT FROM AUTHOR]

This study explores an innovative instrument to monitor potential tilting for an underground structure in a landslide area using computer vision technology. The instrument was composited of the Raspberry Pi, digital cameras, chessboards, and OpenCV programming. Image recognition technology was employed for detection of an inclined angle relevant to pixel changes of the center point on a chessboard in a computer vision–based tiltmeter. For laboratory testing, the resolution and accuracy of the tiltmeter were 0.01 and 0.03°, respectively. For field testing, five computer vision tiltmeters were installed in a drainage tunnel that was constructed under the ground in 80-m depth within a landslide area to monitor potential tilting of the tunnel from January to October in 2018. Maximum change in inclined angles of the five computer vision tiltmeters was 0.04° in the period. Overall, the computer vision tiltmeter for the inclined monitoring of the drainage tunnel is more cost-effective, real-time, and IoT-based than traditional monitoring devices in the landslide area. [ABSTRACT FROM AUTHOR]

We analyzed Global Navigation Satellite System (GNSS) data from 1 January 2008 to 31 January 2016 for the Tokai region of the Nankai subduction zone, in order to study long‐ and short‐term slow slip events (SSEs) on the subduction interface. The dataset included our new temporary stations to obtain high resolution observations with station spacing of about 5 km. Long‐ and short‐term SSEs have been reported in the Tokai region, over the past two decades. It is difficult to directly compare those SSEs because long‐term SSEs were observed by GNSS, while short‐term SSEs were mainly observed by tiltmeters and strainmeters. We applied a time‐dependent inversion with improved temporal resolution to GNSS data and successfully obtained the spatiotemporal evolution of long‐ and short‐term SSEs. Our results show the very slow and stable slip of a long‐term SSE with Mw 6.6, along with several episodes of accelerated slip associated with short‐term SSEs (Mw 6.0–6.1). Our results showed the details of the migrating slip patterns and slip rates for the short‐term SSEs and possible relation with low frequency tremor (LFT). LFT is more associated with smaller magnitude short‐term SSEs rather than the larger long‐term SSEs. However, the maximum daily slip rates for short‐term SSEs are an order of magnitude larger than those for the long‐term SSEs. This suggests an explanation that the LFT may be directly related to the loading of the plate interface by the short‐term SSEs. Key Points: Global Navigation Satellite System data and a Network Inversion Filter resolve long‐ and short‐term slow slip events in the Tokai regionSlip migration synchronized with low frequency tremor along strike is resolved from short‐term slow slip event dataSlip rates of shallower long‐term slow events without tremors are an order of magnitude lower than those of short‐term ones with tremors [ABSTRACT FROM AUTHOR]

This paper presents some current or potential applications in metrology based on the diamagnetism of pyrolytic carbon (PyC). The magnetic repulsion force acting between a piece of PyC subjected to a magnetic flux can be used as magnetic spring either to control the position of the sensitive sensor element or to detect changes of a physical quantity to be measured. The first part of this paper provides examples briefly described of devices based on the diamagnetism of PyC for measuring mechanical quantities. There are two main configurations for magnetic levitation: one, used for measuring acceleration or inclination for instance, is based on the levitation of a PyC tile above a magnet or set of magnets; In the other, used to measure forces caused for example by contact or buoyancy, it is the permanent magnet that is levitated at a stable height above a fixed PyC tile. The second part describes current work at the Laboratoire Commun de Métrologie (LCM-LNE/CNAM) on the development of new laser power sensors using either diamagnetic force changes by photothermal excitation of electrons or diamagnetic torsion spring. [ABSTRACT FROM AUTHOR]

The strong ground motion of 6 February 2018 M 6.2 Hualien Earthquake triggered a series of co-seismic geomagnetic fluctuations and seismo-traveling atmospheric disturbances (STADs) signatures in infrasonic waves and micro-pressures upon the seismic wave arrival. Networks of 9 QuakeFinder systems, 3 infrasound systems, 2 tiltmeters, 2 micro-barometers, and 11 co-located seismometers are used in this study. Each QuakeFinder system consists of a 3-axes induction magnetometer, an air conductivity sensor, a geophone, and temperature/relative humidity sensors. Co-seismic signatures clearly appear in the induction magnetometers, infrasound systems, and micro-barometers data. The magnetometers register both high- and lowfrequency pulsations. Geomagnetic fluctuations occur upon the seismic wave arrival but last a longer duration, while the STADs lag their co-located seismic waves by about 15 - 45 s. The long-lasting fluctuations recorded by both induction and fluxgate magnetometers suggest that the ground/underground water motion play an important role, which is further conformed by low-frequency fluctuations in the tiltmeter data. In general, the amplitude of geomagnetic fluctuations decays as away from the epicenter. However, unusual large co-seismic geomagnetic fluctuations are detected over areas of the abnormal seismic intensity level and/or the magnetic underground structure with anomalously high susceptibilities. [ABSTRACT FROM AUTHOR]

The paper presents the design idea of the portable vertical pendulum tiltmeter, based on in-depth understanding of the application situation of existing VP vertical pendulum tiltmeter in the field of precursory observation, in order to further broaden the scope of application and tap its market potential. A high precision capacitance micrometer was redesigned, at the same time, it also has an improved high reliability lock pendulum mechanism, automatic zeroing devices and Integrated low power circuit system, these designs make the vertical pendulum tiltmeter portable, but also has high reliability and stability. The portable vertical pendulum tiltmeter can be used for in situ observation with VP vertical pendulum tiltmeter in existing stations. It can be used for regular checking and troubleshooting of existing tiltmeters, and also can solve the problem of data loss during the maintenance of the tiltmeters. Through the experiments, the test results show that the portable vertical pendulum tiltmeter can record earth tide curve, the various performance index have reached or close to the expected design goals. [ABSTRACT FROM AUTHOR]

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 Dunaszekcso (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. [ABSTRACT FROM AUTHOR]

The measurement of inclination on gravity concrete dams using the instrument tiltmeter is described and discussed with special reference on obtained results on the dam 'Đerdap 2' acquired in the three years period. Tiltmetar way of operation is presented both through physical principle of vibrating wire sensors and through described design of the instrument. The influence of the temperature on the measurement of the slope is specially emphasized and presented through temperature correction. Processing the results of real inclination measurements on the dam 'Đerdap 2' with and without temperature correction showed the significant difference. Statistical analysis of measurement data consisted of performed regression analysis and forming of corresponding series with the expected measurement values depending on environmental conditions. At the end we give a summary conclusion on the instrument, the influence of temperature on the measurement and statistical model.

This paper presents a high-precision component-type vertical pendulum tiltmeter based on an FPGA (Field Programmable Gate Array) that improves the utility and reliability of geophysical field tilt observation instruments. The system is designed for rapid deployment and offers flexible and efficient adaptability. It comprises a pendulum body, a triangular platform, a locking motor and sealing cover, a ratiometric measurement bridge, a high-speed ADC, and an FPGA embedded system. The pendulum body is a plumb-bob-type single-suspension wire vertical pendulum capable of measuring ground tilt in two orthogonal directions simultaneously. It is installed on a triangular platform, sealed as a whole, and equipped with a locking motor to withstand a free-fall impact of 2 m. The system utilizes a differential capacitance ratio bridge in the measurement circuit, replacing analog circuits with high-speed AD sampling and FPGA digital signal processing technology. This approach reduces hardware expenses and interferences from active devices. The system also features online compilation functionality for flexible measurement parameter settings, high reliability, ease of use, and rapid deployment without the need for professional technical personnel. The proposed tiltmeter holds significant importance for further research in geophysics.

Highlights • A monolithic folded pendulum as high-sensitivity tiltmeter is proposed. • Compact and scalable light tiltmeter. • Effective sensor for low and very low frequency angular monitoring. Abstract The Extended Folded Pendulum Model is a new model aimed at describing the dynamical behavior of a folded pendulum generically oriented in space. This model highlights an analytic relationship between the folded pendulum orientation, referred to the direction of the gravitational acceleration, and its natural resonance frequency. This new feature is the key element for the implementation of high sensitivity stand-alone DC tiltmeters, opening new typologies of application to folded pendulums. In this paper, we present and discuss this model as extension of classical folded pendulum models, using the Tait–Bryan angles formalism. Experimental results obtained with monolithic folded pendulums configured as DC tiltmeters are discussed in connection with the model predictions, also in view of new interesting applications. [ABSTRACT FROM AUTHOR]

The main goal of this work is to provide real-time access to the data of the NSH tunnel tiltmeters via the Internet. Software is developed that solves this problem and also provides real-time visualization and archiving of data. The solution is based the specialized real-time protocol SeedLink, which ensures lossless data delivery with minimal transmission overhead. In order to simplify access to the device via IPv4 and to protect data from unauthorized access, a secure channel based on virtual private networks has been used. The solution was tested on two tiltmeters installed in the building of the Institute of Physics of the Earth, Russian Academy of Sciences (IPE RAS). Further device testing with an unstable power supply and communication conditions is planned. Therefore, the developed software was ported to energy-efficient ARM computers. Data transmission tests were carried out in the local IPE RAS network and in the wireless network of a mobile network operator. Real-time visualization of data from both tiltmeters and access to the archive are provided in addition to real-time access to data on the IPE RAS website. [ABSTRACT FROM AUTHOR]

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A novel method to map asymmetric hydraulic-fracture propagation using tiltmeter measurements is presented. Hydraulic fracturing is primarily used for oil-and-gas well stimulation, and is also applied to precondition rock before mining. The geometry of the developing fracture is often remotely monitored with tiltmeters--instruments that are able to remotely measure the fracture-induced deformations. However, conventional analysis of tiltmeter data is limited to determining the fracture orientation and volume. The objective of this work is to detect asymmetric fracture growth during a hydraulic-fracturing treatment, which will yield heightgrowth information for vertical fracture growth and horizontal asymmetry for lateral fracture growth or detect low preconditioning-treatment efficiency in mining. The technique proposed here uses the extended Kalman filter (EKF) to assimilate tilt data into a hydraulic-fracture model to track the geometry of the fracture front. The EKF uses the implicit level set algorithm (ILSA) as the dynamic model to locate the boundary of the fracture by solving the coupled fluid-flow/fracture-propagation equations, and uses the Okada half-space solution as the observation model (forward model) to relate the fracture geometry to the measured tilts. The 3D fracture model uses the Okada analytical expressions for the displacements and tilts caused by piecewise constant-displacement discontinuity elements to discretize the fracture area. The proposed technique is first validated by a numerical example in which synthetic tilt data are generated by assuming a confining-stress gradient to generate asymmetric fracture growth. The inversion is carried in a two-step process in which the fracture dip and dip direction are first obtained with an elliptical fracture-forward model, and then the ILSA-EKF model is used to obtain the fracture footprint by fixing the dip and dip direction to the values obtained in the first step. Finally, the ILSA-EKF scheme is used to predict the fracture width and geometry evolution from real field data, which are compared with intersection data obtained by temperature and pressure monitoring in offset boreholes. The results show that the procedure is able to satisfactorily capture fracture growth and asymmetry even though the field data contain significant noise, the tiltmeters are relatively far from the fracture, and the dynamic model contains significant "unmodeled dynamics" such as stress anisotropy, material heterogeneity, fluid leakoff into the formation, and other physical processes that have not been explicitly accounted for in the dynamic ILSA model. However, all the physical processes that affect the tilt signal are incorporated by the EKF when the tilt measurements are used to obtain the maximum likelihood estimates of the fracture widths and geometry. [ABSTRACT FROM AUTHOR]

Elastostatic measurements of deformations by using tiltmeters located at moderate to large distances from a hydraulic fracture have often been used to map fracture geometry. The fracture is generally modeled as a quasi-static elastic dislocation, and the analytical solution for the induced deformation by the dislocation in a homogeneous elastic material is commonly used as a forward model to map the fracture geometry by fitting the deformation measurements. However, the mechanical properties of the reservoir in which a hydraulic fracture is placed are often very different from those of the surrounding rocks. In order to obtain a correct interpretation of the created fracture geometry, the mechanical property contrasts need to be recognized and taken into account. In this paper, a mechanical model is presented and applied to the problem of calculating the far-field deformation and stresses induced by a fracture in a reservoir with mechanical properties different from those of the otherwise homogeneous elastic half-space. The fracture is modeled as a constant displacement discontinuity over the fracture plane, and the corresponding eigenstrain associated with the fracture is defined based on the geometries of the fracture and reservoir. Analytical expressions connecting the induced far-field deformation and stresses with the geometrical and mechanical properties of the inhomogeneous system have been established based on the equivalent inclusion method. The proposed model offers a simple and computationally efficient method to account for the effect of inhomogeneous mechanical properties on the far-field deformation induced by the fracture, which can then be used to undertake tiltmeter mapping of the fracture geometry. The mechanical model is verified by comparing with finite element results and analytical solutions available in the literature. [ABSTRACT FROM AUTHOR]