On September 1, 2015, an Mw 5.9 interplate earthquake occurred near the Bonin Trench. An array of in situ ocean‐bottom absolute pressure gauges (APGs) observed its tsunami generation field consisting ...of static and dynamic pressure changes due to tsunami and crustal deformation and due to seismic motion, respectively, under much higher station density than ever reported. We propose an approach to synthesize the pressure change inside the focal area, which reproduces the APG waveforms well. We further successfully estimate the finite fault model of the earthquake and constrain the rupture duration only from the APG data. The relatively low stress drop and seismic wave radiation from the fault model may suggest the nature of a tsunami earthquake. The in situ APGs have a large potential to reveal the broadband source process of the earthquake, which is essential to understand the seismotectonics in the subduction zone.
Plain Language Summary
Absolute pressure gauges (APGs) installed on the seafloor have been widely used to observe various phenomena such as tsunamis. When an APG is located inside a subseafloor earthquake source region, the tsunami generation field is observed, which includes not only tsunamis but also dynamic pressure changes related to seafloor dynamic motion during the earthquake fault slip. This study analyzed densely distributed APG array data, which contained the tsunami generation field of a magnitude‐5.9 earthquake that happened near the Izu‐Bonin Trench on September 1, 2015. This observation was performed by APG stations at higher station density than any data ever reported. This study synthesized this APG array data using the theory for tsunami generation and propagation, and the result explained the data dramatically well. This indicates the validity of the tsunami generation theory for actual observation inside the earthquake source area. We also estimated the slip distribution across the fault of this earthquake, which could not previously be obtained. Our results indicate the combination of APG data obtained inside the focal area and the theory for tsunami generation and propagation is useful for extracting the detailed information on the earthquake rupture process.
Key Points
We examined pressure changes inside the source region of the 2015 Bonin Mw 5.9 EQ where long‐period seismic waves overlap with tsunamis
A numerical simulation for a fluid‐elastic medium was conducted for the pressure change synthetics above the seafloor
Analyzing both tsunamis and dynamic ground motions enabled us to estimate the stress drop and the rupture duration of the Mw 5.9 event
Recent studies have shown that ocean‐bottom pressure gauges (OBPs) can record seismic waves in addition to tsunamis and seafloor permanent displacements, even if they are installed inside the focal ...area where the signals are extremely large. We developed a method to extract dynamic ground motion waveforms from near‐field OBP data consisting of a complex mixture of various signals, based on an inversion analysis along with a theory of tsunami generation. We applied this method to the OBP data of the 2011 Tohoku‐Oki earthquake. We successfully extracted the low‐frequency vertical seismograms inside the focal area (f < ∼0.05 Hz), although those of the Mw ∼9 megathrust earthquake had never previously been reported. The seismograms suggested two dominant energy releases around the hypocenter. The seismic wave signals recorded by the near‐field OBP will be important not only to reveal earthquake ruptures and tsunami generation processes but also to conduct real‐time tsunami forecasts.
Plain Language Summary
During tsunami generation, different types of waves such as ground motions, ocean acoustic waves, and tsunamis coexist inside the focal area, forming complicated wavefields and pressure changes at the sea bottom. This study developed a method to appropriately decompose the complicated ocean‐bottom pressure gauge (OBP) waveforms into ground motion and tsunami signals. Our method was applied to the near‐field OBP data of the 2011 Tohoku‐Oki earthquake to extract the near‐field seismic motion waveform which had never been reported previously. The waveform suggested a complex earthquake rupture process along the plate boundary, in which the rupture happened twice near the hypocenter. The seismic wave signals recorded by the near‐field OBP will be important not only to reveal the processes of the earthquake rupture and tsunami generation but also to issue tsunami alarms.
Key Points
We develop a method to extract low‐frequency ground motion including permanent deformation from ocean‐bottom pressure gauge (OBP) data
We obtain the seismograms inside the focal area of the 2011 Tohoku‐Oki EQ, which suggest two dominant energy releases around the hypocenter
High‐frequency near‐field OBP signals should be utilized more widely for geophysical research as well as real‐time tsunami forecasting
The eruption of the Hunga Tonga–Hunga Ha’apai volcano on 15 January 2022 was the first powerful explosive eruption in history to be recorded with high quality by a wide range of geophysical ...equipment. The atmospheric Lamb wave caused by the explosion repeatedly circled the Earth and served as one of the reasons for the formation of tsunami waves. In this paper, the Lamb wave manifestations are analyzed in the recordings of tsunamimeters, i.e., in data from DONET and DART pressure sensors located in the area of the Japanese Islands. The work is aimed at studying the physics of the formation of pressure variations at the ocean floor in order to develop a method for isolating free gravity waves in records obtained by bottom pressure sensors. Within the framework of shallow water theory, an analysis of the response of the water layer to the atmospheric Lamb wave was performed. This response combines a forced perturbation, the amplitude of which depends on the depth of the ocean, and free gravity waves arising as a result of the restructuring of the forced perturbation on the submarine slopes. Analytical formulas are given for the amplitude and energy of the forced perturbation and free waves arising at the depth jump. With the aid of numerical simulation, the finite length of a slope was revealed to significantly affect the parameters of free waves when exceeding 50 km. The analysis of in situ data (DONET, DART) confirms the validity of theoretical concepts presented in the work. In particular, it is shown that variations of bottom pressure in the deep ocean exceed the amplitude of atmospheric pressure fluctuations in the Lamb wave.
This study reports an ocean‐bottom pressure gauge (OBP) network, S‐net, which captured meteotsunamis with amplitudes as small as a few cm, and investigates its validity and limitation for ...meteotsunami research studies through data analyses and numerical simulations. On July 1, 2020, S‐net recorded tsunami‐like signals, although no earthquake was reported. These waves, propagating northward with a velocity of ∼110 m/s, were explained by an atmospheric low pressure with a maximum amplitude of −0.5 ± 0.1 hPa moving northeastward at a speed of 45–50 m/s. The maximum amplitudes of the sea‐surface height during the low‐pressure passing were up to twice larger than those directly converted from the ocean‐bottom pressure without considering the effect of the atmospheric pressure. Our results suggest that the S‐net with numerical simulations can detect the generation and propagation of meteotsunamis, which could not be achieved in the past when dense OBP networks were not available.
Plain Language Summary
Recent developments in deep‐ocean tsunami observation networks using ocean‐bottom pressure gauge sensors have been remarkable, which have an advantage of continuously monitoring the ocean. On July 1, 2020, a deep‐ocean observation network off eastern Japan, S‐net, recorded small tsunami‐like ocean waves. Although tsunamis are often excited by earthquakes, no earthquake was reported at that time. We investigated the observed feature of these waves, which suggests that the waves were meteorological tsunamis, or meteotsunamis, originating from an atmospheric pressure disturbance. To investigate the behavior of these waves in detail, we conducted numerical meteotsunami simulations. The maximum amplitudes of the sea‐surface height during the atmospheric low‐pressure passing were up to twice larger than those expected from the observed seafloor pressure change without considering the contribution of the atmospheric pressure disturbance. We demonstrated that analyzing the data from the wide and dense array of S‐net made it possible to understand the behavior of the meteotsunamis in detail, which could not be achieved in the past when only a few pressure gauges were available. The S‐net's continuous monitoring of the seafloor pressure in the deep ocean will contribute to deepening our understanding of oceanography and meteorology.
Key Points
Deep‐ocean pressure gauge array observation off NE Japan detected nonseismic tsunami‐like pressure signals with amplitudes of several hPa
A numerical simulation revealed that the signals were meteotsunamis related to a northeastward‐moving atmospheric low pressure
It is necessary to consider the effects of the atmospheric pressure to appropriately estimate sea‐surface height from seafloor pressure gauge
•In-situ measurement of neutral pressure in divertor region was successfully achieved by ASDEX gauge in EAST tokamak.•The in-situ measurement is ∼ 100 ms faster, and more sensitive than the ...conventional gauge located on the port far away from divertor region.•The in-situ measurement by ASDEX gauge shows stable performance in over 200 s long pulse discharges and in >10 MW heating power discharges.
In the tokamak plasma operation, divertor neutral particles play a key role in the study of fuel recycling, heat load mitigation, plasma confinement, and so on. Therefore, the in-situ measurement of neutral pressure in the divertor region is essential for the divertor physics studies. Two ASDEX pressure gauges were installed in the lower divertor dome region and passive plate region, respectively, for the in-situ pressure measurement. Experimental results show that, the ASDEX pressure gauge diagnostic is more sensitive, and its measurement on divertor neutral pressure is about 100 milliseconds faster than the external gauge of the divertor. Moreover, the ASDEX pressure gauge diagnostic is applicable for long pulse and high power plasma operation, and the in-situ pressure measurement of the divertor during over 200 s and higher than 10 MW discharges were successfully achieved in EAST. In addition, ASDEX pressure gauge diagnostic sensitively reacts to the changes in plasma parameters, and the neutral pressure is found to be significantly influenced by the plasma heating power. These results provide powerful technical support for the key divertor physical studies in EAST tokamak and the future fusion devices.
Monitoring long‐term vertical seafloor displacements at the centimeter scale using a pressure gauge network in the seismogenic zone is key to understanding the real‐time strength of interplate ...coupling. The mobile pressure calibrator (MPC) was developed for calibrating a seafloor pressure gauge network with a resolution of less than 1 hPa/year, equivalent to about 1 cm/year. Inherent drift of the seafloor pressure gauges is estimated by comparing the raw observations between the seafloor pressure gauges and the MPC and subsequently subtracting the long‐term pressure data. In October 2018, three in situ pressure measurements were conducted to evaluate the measurement uncertainty of the MPC. The calibrator was placed adjacent to a seafloor pressure gauge, which is installed at a depth of about 1,750 m in the Nankai Trough offshore Japan, and measured the pressure differences between the calibrator and the seafloor pressure gauge. The drift component of the pressure gauge used inside the MPC was estimated and corrected based on calibrations performed in the laboratory before and after the in situ seafloor pressure measurements. The results indicated an uncertainty of 0.04 hPa for the in situ measurements and therefore the possibility of detecting small, long‐term seafloor displacements. We continue to compare the MPC and seafloor pressure gauge deviations over intervals of several months to years and estimate the drift of the seafloor pressure gauge.
Plain Language Summary
In the Nankai Trough, Japan, large earthquakes have repeatedly occurred. The Dense Ocean floor Network system for Earthquakes and Tsunamis (DONET) consisting of 51 observatories, each equipped with a pressure gauge to study vertical deformation and tsunami signals, was installed spanning the region. Crustal deformation is a key parameter for estimating plate coupling strength in subduction zones. The DONET pressure gauge network could be useful for measuring long‐term vertical deformation; however, pressure gauges inherently drift at rates up to 10 hPa/year, about 10 cm/year, which likely exceed seafloor displacement rates. It is necessary to correct gauge drift to reliably detect small seafloor displacements. The mobile pressure calibrator (MPC) was developed to correct drift within the DONET pressure gauge network and enable seafloor displacement measurements on the order of 1 cm. In October 2018, we conducted three pressure measurements at a DONET pressure gauge to evaluate the MPC accuracy. We determined an uncertainty of 0.04 hPa, 0.04 cm equivalent, which should enable seafloor vertical displacement measurements better than 1 cm. Continued DONET pressure gauge MPC calibrations could enable high‐density and real‐time vertical displacement measurements above the seismogenic zone and contribute to understanding plate coupling strength and earthquake and tsunami hazards.
Key Points
A mobile pressure calibrator (MPC) was developed for calibration of seafloor pressure gauges to detect long‐term crustal deformations
In situ pressure measurements were conducted to determine the MPC accuracy of 0.04 hPa, corresponding to a water depth equivalent of 0.04 cm
The results indicate the possibility in the future to calibrate a wide pressure gauge network with a resolution better than 1 hPa/year
We propose a method of tsunami waveform inversion to accurately estimate a tsunami source by incorporating the effect of permanent seafloor deformation recorded by ocean‐bottom pressure gauges ...(OBPGs) within the source region. We developed a general expression of water‐depth fluctuation recorded at an OBPG following seafloor deformation of arbitrary spatiotemporal distribution. By assuming that coseismic rupture propagates with infinite velocity, the general expression can be reduced to an equation relating observed OBPG waveforms to initial sea‐surface displacement at the source by using a Green's function consisting of two terms: the Green's function used in regular tsunami inversion and a correction term to account for water‐depth change in response to permanent seafloor deformation. By using the two‐term Green's functions, the effect of seafloor deformation can be taken into account in tsunami source estimation. We applied the revised inversion method to observations of coseismic seafloor deformation and tsunami during the 2003 Tokachi‐oki earthquake (Mw 8.3) at two OBPG stations near the Kuril Trench. The tsunami source model we estimated is consistent with models previously derived using various other geophysical data sets. Furthermore, the coastal tsunami waveforms we modeled match the observed tsunami well. Forecasts of tsunami arrival times and first peak amplitudes by our method can be obtained 20 min after an earthquake, and can be provided to the coastal communities nearest to the source with a lead time of ∼10 min.
Key Points
Developed tsunami inversion using ocean‐bottom pressure data within the source
Accurate estimate of tsunami source of M8 earthquake by applying our method
Tsunami forecasts for the coast close to the source with a lead time of 10 min
Display omitted
•High-pressure luminescence of strontium borate doped with samarium (II).•High-Pressure nanomanometry based on emission red-shift of SrB2O4:Sm2+ NPs.•Luminescent, lanthanide doped ...nanoparticles as optical nano-sensors of pressure.•Sm2+-doped inorganic nanomaterial working as high pressure gauge.•Luminescence shift of Sm2+ 0-0 line for precise, high-resolution pressure sensing.
A new, non-contact optical sensor of pressure based on the SrB2O4:Sm2+ nanoparticles has been successfully synthesized via a simple and low-cost Pechini method. The obtained nanomaterial was thoroughly characterized using powder X-ray diffraction, transmission electron microscopy, and Raman and luminescence spectroscopies, including high-pressure and high-temperature extreme conditions measurements. Compression of the material leads to a significant red-shift of the intraconfigurational 5D0→7FJ (J = 0−3) emission bands, and to an increase of the Raman mode energies, whose shift rates as a function of pressure were determined. The shift of the extremely sharp and the most intense 5D0→7F0 emission band (Δλ ≈0.24 nm/GPa; Γ (FHWM) ≈0.15 nm) has been used for the determination of the pressure calibration curve. The high-temperature luminescence measurements revealed a desirably weak temperature dependence of the peak spectral position, which was included in the determined pressure calibration curve. The SrB2O4:Sm2+ nanomaterial studied exhibits a negligible temperature-induced emission lines broadening, and relative low thermal quenching of luminescence. The use of such Sm2+-based contactless pressure nano-sensor allows a very accurate pressure sensing ( ± 0.01 GPa), in the sub-micro sized regions, both at low and high temperature conditions.
An array of 10 absolute pressure gauges (APGs) deployed in deep water 50 km east of Aogashima, an island in southern Japan, observed several isolated signals in the infragravity wave (IGW) frequency ...band (0.002–0.03 Hz) during boreal summer, whereas relatively high IGW energy persisted during boreal winter. The isolated IGW shows dispersion with a delay time of 4–5 days as a function of frequency. Here we estimate the excitation locations of IGWs for the two seasons with estimated incoming direction of IGW, calculation of transoceanic IGW trajectories and propagation times, and spatiotemporal variations of significant wave heights from WAVEWATCH III. In boreal summer, the isolated IGWs are primarily caused by IGW energies excited at the shoreline of South America, based on the following three observations: IGWs observed at the array originated from the east: the easterly ray path from the array reaches South America: and an event‐like IGWs were observed at the array when a storm approaches eastward to the shoreline of South America, in which the observed delay time of 4–5 days was also supported by the frequency‐dependent calculation of IGW propagation times. In boreal winter, the incessant IGWs consist of transoceanic IGW energies leaked from the shoreline, primarily from North America, and secondly from South America and the western Aleutian Islands.
Key Points
An APG array observed event‐like IGWs and incessant high IGW energy during boreal summer and winter, respectively
The IGWs in boreal summer are excited at the shoreline of South America
The incessant IGW energy originates primarily from North America, and secondarily from South America and the western Aleutian Islands
We inverted the 2010 Maule earthquake tsunami waveforms recorded at DART (Deep‐ocean Assessment and Reporting Tsunamis) stations in the Pacific Ocean by taking into account the effects of the ...seawater compressibility, elasticity of the solid Earth, and gravitational potential change. These effects slow down the tsunami speed and consequently move the slip offshore or updip direction, consistent with the slip distribution obtained by a joint inversion of DART, tide gauge, GPS, and coastal geodetic data. Separate inversions of only near‐field DART data and only far‐field DART data produce similar slip distributions. The former demonstrates that accurate tsunami arrival times and waveforms of trans‐Pacific tsunamis can be forecast in real time. The latter indicates that if the tsunami source area is as large as the 2010 Maule earthquake, the tsunami source can be accurately estimated from the far‐field deep‐ocean tsunami records without near‐field data.
Key Points
DART data inversion with new Green's functions produces slip distribution similar to joint inversion
Inversion of near‐field DART data can be used for real‐time tsunami forecast at far field
Tsunami source can be accurately estimated from far‐field DART data only
PDF
