Differential Pressure Gauge Research Articles

A Passive-Source Ocean-Bottom Seismic Experiment in the South China Sea: Evaluations of Data Quality and Instrument Performance

Abstract This study presents a passive-source ocean-bottom seismograph (OBS) experiment conducted in the southwest subbasin of the South China Sea (SCS) aimed at exploring the geodynamic processes shaping this short-lived oceanic basin. The successful deployment and recovery of 24 passive-source OBS units, including 14 I-7C types and 10 Pankun OBS units, resulted in the acquisition of one of the most extensive passive-source seismic data sets ever recorded in the SCS. We provide comprehensive details of the experiment, with a focus on evaluating the data quality and performance of the Pankun OBS units. This evaluation includes assessments of horizontal orientation determination, leveling system effectiveness, timing accuracy, and ambient noise spectrum. In addition, we compared the waveforms recorded by the Pankun OBS units with those from land stations and I-7C units, as well as the noise spectra between Pankun and global OBSs using the same seismometer. Although these comparisons suggest that the Pankun OBS achieves satisfactory performance, we identified a few inadequacies with this new instrument, such as issues with the differential pressure gauge, clock shifts, and sensor package calibration.

Investigation on the pressure drop characteristics of ITER thermal shield cooling pipes

This paper presents the experimental results of the pressure drop through the cooling pipes of the ITER Thermal Shield (TS) panels. High pressure and room temperature nitrogen gas is selected for the experiment, which is equivalent operating condition with the 80 K helium gas from fluid mechanics point of view. Flow rate is set by a mass flow controller and pressure difference between the inlet and the outlet of the cooling pipe is measured by a differential pressure gauge. The experimental set-up is open loop type, which is connected to high pressure gas bottle. Flexible corrugated pipes are used to connect the TS cooling pipes with the measurement system line. The effect of the corrugated pipe is evaluated separately and excluded from the measurement results of the TS pipes. Test results of several TS panels are shown in this paper and are compared with the calculation using existing friction factor correlation and local loss coefficient of the pipe bends. The limitation of the calculation is discussed considering the hydrodynamic developing flow in the pipe routing.

BUILDING A MATHEMATICAL MODEL OF THE BIOGAS COMBUSTION PROCESS

During the experimental work thermodynamic methods of measuring the flow of water vapor and hydrogen-oxygen mixture on the basis of differential pressure gauges, methods of contact and non-contact temperature measurement in the superheated, permeable layer of biomass, tried and tested standard methods of synthesis gas analysis using chromatograph and flow gas analyzer were used. Proven mathematical models and proven reliable methods were used in mathematical modeling. Research methods include experimental studies to establish the effect of temperature conditions of gasification, properties of feedstock on the qualitative composition and quantitative yield of synthesis gas; modeling process of carbon-bearing substances gasification with the solution of the resulting model by iteration-interpolation method.

Determination of the design velocity of the gas flow in coarse and fine filters with varying degrees of contamination in the paint booths

OBJECT. Determination of the design velocity of the gas flow in coarse and fine filters with varying degrees of contamination. METHODS. We carried experimental studies out to solve the problem. To exclude errors during the studies caused by marriage or other reasons, 3 samples of each of the coarse and fine filters (clean and used) were used. To determine the design speed, an experimental installation was assembled, presented in the work, which included an air duct, an air injection fan, a nozzle for measuring excess pressure in front of the filter under study, an air vent hole, filter samples, a ventilation grate and measuring instruments – a differential pressure gauge testo 510i and an anemometer testo 405i. RESULTS. The article describes the relevance of the topic, analyzes the change in the pressure drop in the duct when using spent and clean coarse and fine filters. They showed that an increase in their operational life is possible with the use of a multi-vortex separator, which can be installed as a preliminary stage of purification. CONCLUSION. The estimated gas flow velocity when using coarse filters is only 2 m/s. The estimated gas flow velocity when using fine filters is only 0.5 m/s. A comparison of the difference in the pressure drop in the duct when using coarse and fine (spent and clean) filters shows that coarse filters are more susceptible to dusty flow, i.e. the bulk of particles in the dusty flow at an enterprise with paint chambers are relatively large particles. Hydraulic resistance increases by 1.58 times.

Theoretical Solution and Applications of Ocean Bottom Pressure Induced by Seismic Waves at High Frequencies

AbstractPrevious studies have demonstrated that the ocean‐bottom pressure associated with seismic seafloor motion is linearly proportional to the vertical seafloor acceleration, for frequencies much lower than the resonance frequency of water layer (c0/4h, c0 water sound speed, h water depth). In this article, we use realistic observations to verify a theoretical relation between the ocean‐bottom pressure and vertical acceleration up to the water resonance frequency. We then show two applications of the theoretical relation. First, the pressure amplitude recorded by differential pressure gauges is calibrated, and the calibration coefficient is found to vary by frequency. Second, Rayleigh wave phase velocity near the water resonance frequency can be calculated from recordings of pressure and vertical seafloor acceleration at a single station, which is useful to constrain the shallow Earth structure.

Optimization management of installations at groundwater deironing and sewage treatment

In modern conditions, the increase in anthropogenic pressure on the environment discharge of significant amounts of untreated or insufficiently treated wastewater into natural water bodies leads to a deterioration of water quality in sources of drinking water. Therefore, not only conceptual efforts to prevent environmental pollution and provide consumers with quality drinking water are of great importance, but also the mechanisms for their implementation should be revealed. In this aspect, one of the main tasks is the introduction of the latest tools, materials and designs of water treatment facilities and quality control of water supplied to consumers or discharged into natural sources. Pollution entering water bodies changes their physicochemical and biological parameters and leads to complications in the operation of water supply facilities. The solution of these problems is facilitated by the use of advanced technologies for the treatment of both drinking and wastewater. No less important is the establishment of optimal modes of operation of water treatment plants, which ensures maximum efficiency of their operation, conservation of water and energy resources, obtaining guaranteed quality of purified water. The article substantiates the use of natural mechanisms in the processes of deironing of water from underground sources and wastewater treatment. The generalized analysis of the operation of the units with bioreactor and contact clarifier filter during the filter cycle revealed that the standard quality of filtered water is ensured only between the minimum Gmin and maximum Gmax specific dirt content of the filter. It is offered to carry out automation of management of work of such installations at control by the differential pressure gauge of the maximum losses of pressure on the filter corresponding to Gmax value, with its switching to the washing mode. When washing the filter, it is necessary to reduce the specific amount of activated sludge from Gmax to Gmin, controlling the duration of washing the specified intensity with a timer. The proposed measures provide significant savings in water and electricity costs during operation.

Tracking deep-sea internal wave propagation with a differential pressure gauge array

Temperature is used to trace ocean density variations, and reveals internal waves and turbulent motions in the deep ocean, called ‘internal motions.’ Ambient temperature detected by geophysical differential pressure gauges (DPGs) may provide year-long, complementary observations. Here, we use data from four DPGs fixed on the ocean bottom and a high-resolution temperature sensor (T-sensor) 13 m above the seafloor as a square-kilometer array deployed offshore ~ 50 km east of Taiwan facing the open Pacific Ocean to examine the impact of temperature on DPG signals related to internal motions. The DPG signals correlate with T-sensor temperature variations between 0.002 and 0.1 mHz, but have time shifts partially caused by slow thermal conduction from the ambient seafloor to the DPG chamber and partially by internal motion propagation time across the array. Applying beamforming-frequency-wavenumber analysis and linear regression to the arrayed T-sensor and DPG data, we estimate the propagating slowness of the internal motions to be between 0.5 and 7.4 s m−1 from the northwest and northeast quadrants of the array. The thermal relaxation time of the DPGs is within 103–104 s. This work shows that a systematic scan of DPG data at frequencies < 0.1 mHz may help shed light on patterns of internal wave propagation in the deep ocean, especially in multi-scale arrays.

Direct Comparison of the Tsunami‐Generated Magnetic Field With Sea Level Change for the 2009 Samoa and 2010 Chile Tsunamis

AbstractThe motion of conductive seawater by tsunamis can generate magnetic fields in the presence of the background geomagnetic main field. Previous studies found that, using the tsunami‐generated seafloor magnetic field, it is possible to predict the propagation direction and wave height prior to the actual arrivals of tsunamis. This study correlates the tsunami magnetic field and the tsunami sea level change using observed data and three‐dimensional simulations of the 2009 Samoa and 2010 Chile tsunamis. Our direct comparison of the tsunami observed magnetic field and tsunami sea level change illustrate that the vertical tsunami magnetic component, , arrived earlier than the sea level change. The “initial rise” signal in the observed horizontal tsunami magnetic component, , which was arrived even earlier than also is found by combing the observation with the three‐dimensional simulations. We further examine the precision of conversion of the tsunami magnetic field to the sea level change and find that the magnetic field derived tsunami sea levels are as precise as those obtained from differential pressure gauge data. However, our simulation shows that existing tsunami source models are incompatible with our tsunami magnetic data. Therefore, it is necessary to include magnetic field derived tsunami sea level changes to improve those source models.

MODEL OF PNEUMOMETRIC DENSITY METER FOR MEASURING THE DENSITY OF DRILLING SOLUTIONS OF OIL AND GAS WELLS

The development of automatic pneumometric densitometers is promising not only for drilling fluids. They can be used in the food, chemical, refining, oil depots and storage facilities. Based on them, you can build systems for quantitative accounting of liquid products in units of mass. Possessing high accuracy, pneumometric densitometers are simple and reliable, convenient in operation and, most importantly, are completed with the elements serially issued by the industry.&#x0D; The article presents a block diagram of a differential pneumometric densitometer with ballast pressure compensator in the minus pneumoline and shows the calculation which shows that the main source of error is the pressure loss in the pneumolines, zero drift of the differential pressure gauge, cancellation of real values ​​of static coefficients from differential. It is pointed out that in order to find the value of pressure and flow at each point of the pneumoline, even for simple models, it is necessary to make complex calculations. An analytical solution can only be obtained for individual cases that are of no practical value.&#x0D; Therefore, for the analysis of a pneumoline of a densitometer it is most rational to use a method of electrohydraulic analogy (EGDA) and to pass from a pneumatic line with the distributed parameters to similar electric with rarefied parameters. We obtained a model of a pneumometric densitometer in the form of an electrical circuit, which requires further research, electrical engineering methods, to clarify the coefficients and parameters of the model and check its adequacy.

Near-Field Body-Wave Extraction From Ambient Seafloor Noise in the Nankai Subduction Zone

Ambient noise correlation is capable of retrieving waves propagating between two receivers. Although waves retrieved using this technique are primarily surface waves, the retrieval of body waves, including direct, refracted, and reflected waves, has also been reported from land-based observations. The difficulty of body wave extraction may be caused by large amplitudes and little attenuation of surface waves excited by microseisms, indicating that body wave extraction using seafloor records is very challenging because microseisms are generated in ocean areas and large amplitudes of surface waves are presumably observed at the seafloor. In this study, we used a unique dataset acquired by dense arrays deployed in the Nankai subduction zone, including a permanent cabled-network of 49 stations, a borehole sensor, and 150 temporary stations, to attempt to extract near-field body waves from ambient seafloor noise observed by multivariate sensors of broadband and short-period seismometers, differential pressure gauges (DPGs), and hydrophones. Our results show thatPwaves are extracted only in the DPG-record correlations at a frequency of 0.2–0.5 Hz, which can be seen up to a separation distance of two stations of 17 km with an apparent velocity of 3.2 km/s. At 1–3 Hz,Pwaves are observed only in the vertical-record correlations up to a separation distance of 11 km with an apparent velocity of 2.0 km/s. These velocity differences reflect the vertical velocity gradient of the accretionary prism, because thePwaves at low frequencies propagate at relatively long distances and therefore the turning depth is greater. Moreover, the long-period and short-periodPwaves are observed at the slope and flat regions on the accretionary prism, respectively. To investigate the retrieved wavefield characteristics, we conducted a two-dimensional numerical simulation for wave propagations, where we located single sources at the sea surface above the flat and slope bathymetry regions. Based on our observations and simulations, we suggest that the retrieval of near-field body waves from ambient seafloor noises depends on the relative amplitudes ofPand other surface waves in the ambient noise wavefield, and those are controlled by the subseafloor velocity structure, seafloor topography, and water depth.

К ВОПРОСУ НЕПРЕРЫВНОГО КОНТРОЛЯ ПАРАМЕТРОВ ДОБЫВАЕМОЙ ПРОДУКЦИИ НЕФТЯНЫХ СКВАЖИН

Relevance When developing alternating current test voltage sources to assess the quality of insulatioThe article considers the problem of continuous control of technological parameters for effective management of oil fields while reducing material and economic costs. Aims of research To develop a measuring complex for non-stop control of main parameters of the extract products (water content and flow rate) of oil producing wells directly in a column of pumping-compressor pipes. Research methods The method of monitoring the parameters of the flow of oil-water mixture in real time by the proposed complex is based on an indirect method for determining the characteristics of the medium flowing through the upper section of the lift in the form of tubing, using two methods: monitoring the permittivity of the medium using capacitive sensor and monitoring its density a been used differential pressure gauge. In this work the drawing of a measuring complex, a general view of the experimental stand and the structural scheme of the measuring transducer and also research results are submitted. Measurements were carried out by means of the electronic circuit consisting of analog-to-digital converters of dielectric permittivity of the compound connected to the computer for received data processing and visualization by means of the LabVIEW program. Results of conversion of measurements of percentage of water in water oil mix were used in algorithms of obtaining values of moisture content and traverse speed of the compound. Results As a result of researches it is revealed that the developed measuring complex has the acceptable accuracy of measurements of a volume flow of liquid. Use of algorithms of obtaining values of moisture content and traverse speed of the compound provides the required accuracy and speed of obtaining results of the measurements necessary for practical application. Simplicity of its implementation creates conditions for considerable decrease in cost value of implementation on the operating oil fields. Thus, the developed measuring complex for oil wells will allow to carry out non-stop monitoring of parameters of production for the organization an oil field automatic control system.

Study on the method of testing the adsorption and diffusion capacities of coal matrix and its influencing factors using the sliced coal samples

ABSTRACT Through the reasonable design of experimental instrument, the experimental mechanism of adsorption-diffusion of thin sliced coal samples is explored, and a set of rigorous experimental procedures, data acquisition, and processing methods are formed. The method is to grind coal samples into rectangular samples with thickness less than 4 mm and place them in a sealed container. The adsorption and diffusion characteristics of the coal matrix are accurately reflected due to its original internal structure. The three-dimensional diffusion model of the Fick’s second law is simplified to one-dimensional diffusion model, and the diffusion coefficient is calculated. The accuracy of experimental parameters is improved by the instrument combination of sample diffusion test cylinder, pressure reference cylinder and differential pressure gauge. Meanwhile, a set of calculation methods for the adsorption amount and diffusion coefficient of coal slice is proposed. The experimental results indicate that the diffusion coefficient of coal matrix is sensitive to temperature and diffusion path, but insensitive to pressure and fixed carbon content of coal matrix. The adsorption amount is sensitive to the change of fixed carbon content. Meanwhile, the experimental results of different coal samples are basically consistent with the characteristics of the production wells in the mine.

Laboratory Measurements of the Relative Permeability of Coal: A Review

The relative permeability of coal to gas and water is an essential parameter for characterizing coalbed methane (CBM) reservoirs and predicting coal seam gas production, particularly in numerical simulations. Although a variety of studies related to the relative permeability of coals have been conducted, the results hardly meet the needs of practical engineering applications. To track the dynamic development of relative permeability measurements in the laboratory, discover the deficiencies, and discuss further work in this field, this paper investigates the relative permeability measurement preparation work and laboratory methods and summarizes the development of techniques used to determine the water saturation during experimentation. The previously determined relative permeability curves are also assembled and classified according to coal rank and the absolute permeability. It is found that the general operations in the relative permeability measurement process are still not standardized. The techniques applied to determine the water saturation of coal in experiments have been refined to some extent, but no optimal technique has been recognized yet. New techniques, such as the incorporation of high-precision differential pressure gauges, can be used to determine the water production during relative permeability measurement. In addition, the existing relative permeability data are limited, and no study has focused on supercritical carbon dioxide-water and mixed gas (methane and carbon dioxide)-water relative permeability measurements. To meet the requirements of actual projects, further research on this topic must be conducted.

The Alaska Amphibious Community Seismic Experiment

AbstractThe Alaska Amphibious Community Seismic Experiment (AACSE) is a shoreline-crossing passive- and active-source seismic experiment that took place from May 2018 through August 2019 along an ∼700 km long section of the Aleutian subduction zone spanning Kodiak Island and the Alaska Peninsula. The experiment featured 105 broadband seismometers; 30 were deployed onshore, and 75 were deployed offshore in Ocean Bottom Seismometer (OBS) packages. Additional strong-motion instruments were also deployed at six onshore seismic sites. Offshore OBS stretched from the outer rise across the trench to the shelf. OBSs in shallow water (&amp;lt;262 m depth) were deployed with a trawl-resistant shield, and deeper OBSs were unshielded. Additionally, a number of OBS-mounted strong-motion instruments, differential and absolute pressure gauges, hydrophones, and temperature and salinity sensors were deployed. OBSs were deployed on two cruises of the R/V Sikuliaq in May and July 2018 and retrieved on two cruises aboard the R/V Sikuliaq and R/V Langseth in August–September 2019. A complementary 398-instrument nodal seismometer array was deployed on Kodiak Island for four weeks in May–June 2019, and an active-source seismic survey on the R/V Langseth was arranged in June 2019 to shoot into the AACSE broadband network and the nodes. Additional underway data from cruises include seafloor bathymetry and sub-bottom profiles, with extra data collected near the rupture zone of the 2018 Mw 7.9 offshore-Kodiak earthquake. The AACSE network was deployed simultaneously with the EarthScope Transportable Array (TA) in Alaska, effectively densifying and extending the TA offshore in the region of the Alaska Peninsula. AACSE is a community experiment, and all data were made available publicly as soon as feasible in appropriate repositories.

Source Regions of Infragravity Waves Recorded at the Bottom of the Equatorial Atlantic Ocean, Using OBS of the PI‐LAB Experiment

AbstractInfragravity waves are generated along coasts, and some small fraction of their energy escapes to the open oceans and propagates with little attenuation. Due to the scarcity of deep‐ocean observations of these waves, the mechanism and the extent of the infragravity waves energy leakage from the coasts remains poorly understood. Understanding the generation and pathways of infragravity wave energy is important among others for understanding the breakup of ice‐shelves and the contamination of high‐resolution satellite radar altimetry measurements of sea level. We examine data from 37 differential pressure gauges of Ocean Bottom Seismometers (OBS) near the equatorial mid‐Atlantic ridge, deployed during the Passive Imaging of the Lithosphere‐Asthenosphere Boundary (PI‐LAB) experiment. We use the beamforming technique to investigate the incoming directions of infragravity waves. Next, we develop a graph‐theory‐based global back‐projection method of noise cross‐correlation function envelopes, which minimizes the effects of array geometry using an adaptive weighting scheme. This approach allows us to locate the sources of the infragravity energy. We assess our observations by comparing to a global model of infragravity wave heights. Our results reveal strong coherent energy from sources and/or reflected phases at the west coast of Africa and some sources from South America. These energy sources are in good agreement with the global infragravity wave model. In addition, we also observe infragravity waves arriving from North America during specific events that mostly occur during October–February 2016. Finally, we find indications of waves that propagate with little attenuation, long distances through sea ice, reflecting off Antarctica.

Methods and means of the experimental research of the electrothermal arcjet thrusters of spacecrafts

The subject of the research in this article is the measurement of the main characteristics of the electrothermal arcjet thrusters in the process of the working fluid acceleration during the bench tests. The purpose is to form a bench research facility to study the characteristics of the electric heating propulsion system for use in a space tugboat, taking into account the launch dynamics, operating conditions and shutdown dynamics. Tasks: measuring the thrust of the electric propulsion system as the main characteristic in the established and transient mode; determining the flow rate of the working fluid correlated with the thrust; measuring the parameters of electrical consumption ‒ currents, voltage, power in static and dynamic modes; measuring the external conditions of the simulating space environment, namely the vacuum, in the test chamber. The methods used are: tensometry, differential pressure gauge, four-probe measurement of power supplied to engine heaters, steam generator and tank of the electric heating system, ionization-thermocouple vacuum measurement. The following results have been obtained: the composition of the information and control system consisting of the tensometric sensor used with the electric heating propulsion system, flowmeter of the working body of the electric heating propulsion system, power meter of the heater, steam generator and the tank of the electric heating propulsion system, ionization-thermocouple sensors for vacuum determination. The software product for graduation of the tensometric sensor has been developed. The scientific innovation of the obtained results is as follows: the method of measuring the thrust of the electric heating propulsion system by means of tensometric sensor has been further developed, the method of measuring the flow of the working body of the electric heating propulsion system has been further developed, the method of measuring the power of the engine heater, steam generator, tank of the electric heating propulsion system has been further developed. For the first time an algorithm for graduation of the tensometric sensor for the electric heating propulsion system was developed and implemented in the software product.

Shear wave velocity and radial anisotropy structures beneath the central Pacific from surface wave analysis of OBS records

The central Pacific plate is an ideal area to study the dynamics of the lithosphere-asthenosphere system, as this region is far away from other dynamics systems, such as subduction zones and volcanic hotspots of mantle plumes, and has experienced simple oceanic evolution. In this study, we collect three-component continuous seismic data and differential pressure gauge data recorded by 15 broadband ocean bottom seismometers (OBSs) from the NoMelt experiment. We process continuous seismic noise data to obtain phase velocities of the fundamental (6-30 s) and first high (5-11 s) mode Rayleigh waves and fundamental mode Love waves (5-12 s). We apply a two-plane-wave method to teleseismic Rayleigh waves to obtain the fundamental mode phase velocities at 20-150 s periods, and apply high-resolution linear Radon transform to teleseismic Love waves to obtain phase velocities for the fundamental mode Love waves at 28-48 s periods. Then, we jointly invert the average phase velocities of Rayleigh and Love waves to construct 1-D isotropic shear wave velocity and radial anisotropy from the seafloor to 150 km depth beneath the NoMelt region. Our 1-D model shows a low velocity zone (LVZ) beneath a high velocity lid. By comparing our results with the predictions of partial melt models, we suggest the LVZ is attributed to the presence of a small amount of melt in the asthenosphere. Strong radial anisotropy (5-6%) is observed in the crust. But the mantle lithosphere is characterized by weak radial anisotropy (< 1%), consistent with the corner mantle flow history at the mid-ocean ridge during the formation of new oceanic plates. Strong radial anisotropy (4-5%) is observed in the asthenosphere, which is consistent with the global surface wave tomography results and numerical simulation studies, reflecting the strong shear strain of asthenosphere related to the motion of oceanic plate over the underlying asthenosphere.

ТЕОРЕТИЧЕСКИЕ ОСНОВЫ ПРОЦЕССА ОЗОНИРОВАНИЯ ЖИДКОГО ТОПЛИВА И ИЗУЧЕНИЕ ВЛИЯНИЯ МАЛЫХ ДОЗ ОЗОНА НА РАБОТУ КАРБЮРАТОРНОГО ДВИГАТЕЛЯ ВНУТРЕННЕГО СГОРАНИЯ(ДВС)

Theoretical bases and chemistry of ozonation of the fuel during the introduction of the oxidant in both the gas and liquid phases are considered. The mechanisms of chemical processes of intensification of fuel combustion, suppression of the formation of toxic compounds during ozone dosing are presented. The radical-ion mechanism of the chain reactions of the oxidant macroactivity at its microadditives is shown. The possibility of saving liquid fuel has been established. The experimental verification of the effect of ozone small doses on the process of combustion of gasoline in internal combustion engines is presented. Due to the fact that this reaction mechanism is very well studied, this makes it possible to theoretically trace the effect of synthesized compounds. A number of experiments have been carried out, the results of which are presented. The brief technical characteristics of the engine and brake stand are named. Engine fuel consumption has been measured by directly determining the change in fuel mass over time. The flow rate of air consumed by the engine has been measured using a differential pressure gauge. The temperature of the exhaust gases has been measured using a thermocouple. Theoretical foundations of the analytical control of the process, the reduction of carbon monoxide, the effect of ozone on the soot content in the exhaust gases, the change in operational factors during engine operation are described. The use of ozonized gasoline improves such an engine operating parameter as efficiency (fuel economy up to 7 %) and increases its power. Ozone additive in fuel due to the formation of HO• radicals in the volume of the fuel-air mixture, radicals HO•; HО2•; RO2• destroys peroxide compounds, which are the main source of detonation combustion of gasoline.

Post-seismic response of the outer accretionary prism after the 2010 Maule earthquake, Chile

AbstractTo investigate the dynamic response of the outer accretionary prism updip from the patch of greatest slip during the 2010 Mw 8.8 Maule earthquake (Chile), 10 ocean-bottom seismometers (OBSs) were deployed from May 2012 to March 2013 in a small network with an inter-instrument spacing of 7–10 km. Nine were recovered, with four recording data from intermediate-band three-component seismometers and differential pressure gauges, and five recording data from absolute pressure gauges (APGs). All instruments were also equipped with fluid flow meters designed to detect very low rates of flow into or out of the seafloor. We present hypocenters for local earthquakes that have S-P times &amp;lt;17 s (i.e., within ∼125 km of the network), with a focus on events located beneath or near the network. Most of the seismicity occurred either near the boundary between the active accretionary prism and continental basement or in the outer rise seaward of the trench. For many outer-rise earthquakes, the P and S arrivals are followed by a distinctive T-phase arrival. Very few earthquakes, and none located with hypocenters deemed “reliable,” were located within the active accretionary prism or on the underlying plate boundary. Nonvolcanic tremor-like pulses and seafloor pressure transients (but no very-low-frequency earthquakes or fluid flow) were also detected. Many of the tremor observations are likely T-phases or reverberations due to soft seafloor sediments, although at least one episode may have originated within the accretionary prism south of the network. The transient seafloor pressure changes were observed simultaneously on three APGs located over the transition from the active prism to the continental basement and show polarity changes over short distances, suggesting a shallow source. Their duration of several hours to days is shorter than most geodetic transients observed using onshore GPS networks. The results demonstrate the need for densely spaced and large-aperture OBS networks equipped with APGs for understanding subduction zone behavior.

Calibration of marine differential pressure gauges through in situ testing at the seafloor

Differential pressure gauges (DPGs) are a standard component of modern broadband ocean-bottom seismometer instruments and have proven useful for observing a wide range of seismic and oceanographic phenomena. However, the response function of the DPG remains poorly known, limiting our ability to recover amplitude and phase information from seafloor pressure signals with high fidelity. The sensitivity and long-period response are difficult to calibrate in the lab, as they are known to vary with temperature and pressure and perhaps between sensors of the same design. We present the results of a field experiment designed to determine empirical response functions in situ by inducing a pre-defined pressure offset on a deployed instrument. The results compare favorably with calibrations estimated independently through post-deployment data analyses. Our study demonstrates that observed response functions can deviate from the nominal response by a factor of two or greater with regards to both the sensitivity and the time constant. Incorporating calibration devices such as those described here into future deployments may prove to be a cost-effective way to improve the accuracy and utility of differential pressure data.Differential pressure gauges (DPGs) are a standard component of modern broadband ocean-bottom seismometer instruments and have proven useful for observing a wide range of seismic and oceanographic phenomena. However, the response function of the DPG remains poorly known, limiting our ability to recover amplitude and phase information from seafloor pressure signals with high fidelity. The sensitivity and long-period response are difficult to calibrate in the lab, as they are known to vary with temperature and pressure and perhaps between sensors of the same design. We present the results of a field experiment designed to determine empirical response functions in situ by inducing a pre-defined pressure offset on a deployed instrument. The results compare favorably with calibrations estimated independently through post-deployment data analyses. Our study demonstrates that observed response functions can deviate from the nominal response by a factor of two or greater with regards to both the sensitivity and t...