Cable Array Research Articles

Six years of low-frequency underwater noise off the Oregon coast from the OOI Regional Cabled Array System (RCA) and interpretive linkage with RCA Oceanographic Data

Approximately 6 years of underwater noise data recorded from the Regional Cabled Array (RCA) network, at the site known as Hydrate Ridge, is studied for purposes of examining long term trends. The acoustic data originate from station HYS14 located on the seabed at a depth of approximately 800 m and 80 km offshore of Newport, OR. The sample rate is 200 Hz, setting the analysis limit to less than 100 Hz. Seasonal warming results in a highly repeatable annual change in the levels at shipping frequencies (50–70 Hz) of order 4 dB which is out-of-phase with concurrent observations of shipping density. Using data from the shallow-water profiler (RCA station SF03A) the influence seasonal warming on the acoustic observations are studied. It is shown how higher ocean surface temperatures cause mode excitation support to move deeper and away typical ship source depths resulting in less efficient transmission of underwater sound. Deviations in the seasonal trends are also observed and shown to be correlated to atypical climatic events such as the warm water blob event of 2015–2016, and suppressed shipping activity during economic downturns, such as observed during COVID-19.

Combined acoustical and seismic studies of Axial Seamount

The NSF Ocean Observatories Initiatives Regional Cabled Array at Axial Seamount provides a remarkable facility for sustained studies of an active submarine volcano. A local seismic network supports a real-time earthquake catalog and hydrophones monitor sounds in the water column. In April 2015, Axial Seamount erupted shortly after the cabled observatory came on line. The seismic record of brittle deformation in the summit caldera during the eruption is complemented by acoustic observations that tracked a dike propagating along the north rift using T phases and recorded both impulsive and continuous sound sources on the seafloor at the sites of erupting lava. Seafloor pressure gauges are presently documenting the reinflation of the volcano towards its next eruption and these geodetic studies would be enhanced by deploying a transponder network to support horizontal ranging. The availability of real-time data to detect and localize future eruptions will enable effective autonomous and ship-based responses to study how hydrothermal systems and their chemosynthetic biological communities respond to eruptions. The seismic and acoustic networks could also support studies of fin and blue whales to understand whether their distribution is modulated by the enhanced productivity associated with the presence of a hydrothermally active seamount.

Variability of Natural Methane Bubble Release at Southern Hydrate Ridge

AbstractCurrent estimations of seabed methane release into the ocean (0.4–48 Tg yr−1) are based on short‐term observations and implicitly assume that fluxes are constant over time. However, the intensity of gas seepage varies significantly throughout a seep lifetime. We used instruments operated by the Ocean Observatories Initiative's Regional Cabled Array to monitor variations of gas emissions over the entire Southern Hydrate Ridge summit. We show that bubble plumes emanate from distinct and persistent vents. Multiple plumes can occur within each vent and the location of their outlets may shift progressively. Active bubble plumes vary temporally in number and intensity, even within single vents. Gas emission fluctuations are partly periodic and linked to the local tide. However, short‐term variability and high ebullition events unrelated to tidal cycles are also commonly observed. Our data indicate that small‐scale processes beneath or at the sediment surface are responsible for the short‐term variability of the venting activity that is otherwise modulated by tides. Furthermore, a decrease of venting at one vent may coincide with an increase in plume activity at other vents. Our results depict a spatially and temporally dynamic seep environment, the variability of which cannot be fully characterized without systematic and comprehensive monitoring of the entire area. These results indicate that flux estimations may be largely overestimated or underestimated depending on the time, duration, and place of observation. Although sudden ebullition bursts are hardly predictable, we argue that tidal cycles must be taken into consideration when estimating gas fluxes.

Bench-scale experimental study on the fire behavior of electric cable arrays by considering different layouts

The effect of different cable layouts on the fire behavior of electric cable arrays was experimentally studied. The influence of external heat flux on cable fire characteristics was investigated. Several parameters for electrical cables such as the post-burning morphology, ignition time, heat release rate, peak heat release rate and total heat release were obtained. The results show that cable layouts could affect cable charring degrees according to the post-burning morphology. A linear relationship was found in the transformed form of time to ignition and radiant heat flux, and the critical radiant heat flux value for the single cable array appeared smaller than that for the other two layouts. The peak heat release rate for Cables A–D with the single array presents the increasing trend with an increase in radiant heat flux, while the two parallel and intersectional cable arrays present the different trends. Moreover, the total heat release values of Cables A–D in the different cable layouts were analyzed. This work provides the basic data and preliminary investigation to fire engineering of cable arrays with the different layouts.

As Road To Real-Time Fracturing Optimization Is Paved, Shale Producers Approach On-Ramps Cautiously

To say that the shale sector is on the cusp of a new era, one where fast-flowing streams of real-time well data and on-the-fly fracture designs are the norm, is not something one does lightly. It’s a bold declaration. It represents a step change that engineers have been told is just around the corner for several years. They’ve been promised software that will churn out truly optimized recipes of proppant concentration, rate, total volume, etc. to match each fracture stage’s piece of the rock. In a neat world, this nets better production from good stages while injecting less capital into bad stages—the ultimate win-win for a sector that spends 60–70% of well costs on the completion. We can pluck example after example from industry literature to prove the incremental existence of such tailor-made well pads. However, the mostly small-scale cases are far from representative of the aggregate. For some, the absence of scale fuels skepticism over whether real-time optimization will ever amount to much more than avoiding screenouts and other costly operational drags. Then again, history is not always the best predictor of the future. In this context, it discounts a slate of technologies and methods that didn’t exist 5 years ago or were still coming into their own. Some of these innovations are now part of the toolbox that operators are using to reach for the brass ring that is real-time optimization at scale. “Much like self-driving cars, we see the future of a self-driving oil field that’s self-optimizing and operated autonomously—an element of this would be automating the fracturing process,” said Rob Fast, the chief technology officer of the Bakken Shale producer Hess Corp. He added that this vision of the future could be coming soon. Hess and its service provider are scheduled to start the first field trials of an automated fracturing system sometime in June. While sharing details of the upcoming test, Fast emphasized that “this project is a collaboration project that combines automation and optimization and provides advanced measurements to optimize completions and well spacing.” Fast was speaking during the SPE Hydraulic Fracturing Technology Conference plenary where he said the decision to invest in automated fracturing comes after Hess spent more than a decade producing some of the industry’s most in-depth tight reservoir studies. Through that work, the operator has apparently concluded that right sizing fractures will require a reliable set of eyes and ears in the subsurface. That translates to an array of permanent fiber-optic cables and permanent downhole pressure gauges, along with temporary “dip in” fiber deployments. Traditionally, such a big data-giving diagnostic program would be deemed a “science project,” the widely used euphemism for the sector’s illuminating but hard-to-scale look-back studies. But Hess sees dividends if the diagnostic jewelry helps achieve a new ambition to complete 40% fewer wells in the Bakken while still maintaining current recovery estimates. “Serious beef,” Fast said of the sought-after target.

Trends in low-frequency underwater noise off the Oregon coast and impacts of COVID-19 pandemic.

Approximately six years of underwater noise data recorded from the Regional Cabled Array network are examined to study long-term trends. The data originate from station HYS14 located 87 km offshore of Newport, OR. The results indicate that the third-octave band level centered at 63 Hz and attributable to shipping activity is reduced in the spring of 2020 by about 1.6 dB relative to the mean of the prior five years, owing to the reduced economic activity initiated by the COVID-19 pandemic. The results are subtle, as the noise reduction is less than the typical seasonal fluctuation associated with warming ocean surface temperatures in the summer that reduces mode excitation support at typical ship source depths, causing a repeated annual level change on the order of 4 dB at shipping frequencies. Seasonality of the noise contribution near 20 Hz from fin whales is also discussed. Corroboration of a COVID-19 effect on shipping noise is offered by an analysis of automatic identification system shipping data and shipping container activity for Puget Sound, over the same six-year period, which shows a reduction in the second quarter of 2020 by ∼19% and ∼17%, respectively, relative to the mean of the prior five years.

Trends in low frequency ambient noise for a site 80 km off the Oregon coast over approximately four years ending August 2020

Approximately 4 years of underwater noise data recorded from the Regional Cabled Array (RCA) network, at the site known as Hydrate Ridge, is studied for purposes of examining long term trends. The data originate from station HYS14 located on the seabed at a depth of approximately 800 m and 80 km offshore of Newport, OR. The sample rate is 200 Hz, setting to the analysis limit to less than 100 Hz. A distinctive feature of the data is the sound pressure level in the frequency range of 20 Hz that reflects the migratory timing of fin whales, which peaks near the start of the new year, and reaches a minimum around June. There is a suggestion that the level between 10 and 70 Hz attributable shipping activity, is reduced in the spring of 2020 by about 2 dB relative the three prior years, possibly owing reducing economic activity linked with Covid-19. At the time of this writing independent verification of with shipping data is ongoing. [This study was partially supported by U.S. Office of Naval Research and by the UW Cooperative Institute for Climate, Ocean and Ecosystem Studies (CICOES).]

Multi-domain inspection of offshore wind farms using an autonomous surface vehicle

The offshore wind power industry is an emerging and exponentially growing sector, which calls to a necessity for a cyclical monitoring and inspection to ensure the safety and efficiency of the wind farm facilities. Thus, the emersed (aerial) and immersed (underwater) scenarios must be reconstructed to create a more complete and reliable map that maximizes the observability of all the offshore structures from the wind turbines to the cable arrays, presenting a multi domain scenario.This work proposes the use of an Autonomous Surface Vehicle (ASV) to map both domains simultaneously. As such, it will produce a multi-domain map through the fusion of navigational sensors, GPS and IMU, to localize the vehicle and aid the registration process for the perception sensors, 3D Lidar and Multibeam echosounder sonar. The performed experiments demonstrate the ability of the multi-domain mapping architecture to provide an accurate reconstruction of both scenarios into a single representation using the odometry system as the initial seed to further improve the map with data filtering and registration processes. An error of 0.049 m for the odometry estimation is observed with the GPS/IMU fusion for simulated data and 0.07 m for real field tests. The multi-domain map methodology requires an average of 300 ms per iteration to reconstruct the environment, with an error of at most 0.042 m in simulation.

Acoustic and In‐Situ Observations of Deep Seafloor Hydrothermal Discharge: An OOI Cabled Array ASHES Vent Field Case Study

AbstractThe Cabled Observatory Vent Imaging Sonar (COVIS) was installed on the Ocean Observatories Initiative's Regional Cabled Array observatory at ASHES hydrothermal vent field on Axial Seamount in July 2018. The acoustic backscatter data recorded by COVIS in August–September 2018, in conjunction with in situ temperature measurements, are used to showcase and verify the use of COVIS for long‐term, quantitative monitoring of hydrothermal discharge. Specifically, sonar data processing generates three‐dimensional backscatter images of the buoyant plumes above major sulfide structures and two‐dimensional maps of diffuse flows within COVIS's field‐of‐view. The backscatter images show substantial changes of plume appearance and orientation that mostly reflect plume bending in the presence of ambient currents and potentially the variations of outflow fluxes. The intensity of acoustic backscatter decreases significantly for highly bent plumes as compared to nearly vertical plumes, reflecting enhanced mixing of plume fluids with seawater driven by ambient currents. A forward model of acoustic backscatter from a buoyancy‐driven plume developed in this study yields a reasonable match with the observation, which paves the way for inversely estimating the source heat flux of a hydrothermal plume from acoustic backscatter measurements. The acoustic observations of diffuse flows show large temporal variations on time scales of hours to days, especially at tidal frequencies, but no apparent long‐term trend. These findings demonstrate COVIS's ability to quantitatively monitor hydrothermal discharge from both focused and diffuse sources to provide the research community with key observational data for studying the linkage of hydrothermal activity with oceanic and geological processes.

Automated, Cost-Effective Optical System for Accelerated Antimicrobial Susceptibility Testing (AST) Using Deep Learning

Antimicrobial susceptibility testing (AST) is a standard clinical procedure used to quantify antimicrobial resistance (AMR). Currently, the gold standard method requires incubation for 18-24 h and subsequent inspection for growth by a trained medical technologist. We demonstrate an automated, cost-effective optical system that delivers early AST results, minimizing incubation time and eliminating human errors, while remaining compatible with standard phenotypic assay workflow. The system is composed of cost-effective components and eliminates the need for optomechanical scanning. A neural network processes the captured optical intensity information from an array of fiber optic cables to determine whether bacterial growth has occurred in each well of a 96-well microplate. When the system was blindly tested on isolates from 33 patients with Staphylococcus aureus infections, 95.03% of all the wells containing growth were correctly identified using our neural network, with an average of 5.72 h of incubation time required to identify growth. 90% of all wells (growth and no-growth) were correctly classified after 7 h, and 95% after 10.5 h. Our deep learning-based optical system met the FDA-defined criteria for essential and categorical agreements for all 14 antibiotics tested after an average of 6.13 h and 6.98 h, respectively. Furthermore, our system met the FDA criteria for major and very major error rates for 11 of 12 possible drugs after an average of 4.02 h, and 9 of 13 possible drugs after an average of 9.39 h, respectively. This system could enable faster, inexpensive, automated AST, especially in resource limited settings, helping to mitigate the rise of global AMR.

Design of Pre-stressed Cable Rod Radar Array Structure Based on Finite Element Analysis

In recent years, with the increasingly high requirements of radar thinness, the radar array appears thinner and thinner, which is easy to make the stiffness of the radar array is not enough, leading to serious deformation of the radar array, and thus affecting the work of the radar and the whole machine life. As a new type of space structure with light weight and high strength, the pre-stressed cable-stayed structure can play a good role in replacing the traditional front structure. According to the overall design requirements of a radar and the RMSE requirements for the plane flatness, the pre-stressed cable-stayed structure of the radar array is preliminarily designed, and the finite element analysis results are used to optimize the design and finally meet the design requirements.

A Joint Inversion for Three‐dimensional P and S Wave Velocity Structure and Earthquake Locations Beneath Axial Seamount

AbstractAxial Seamount is a prominent volcano located at the intersection of the Juan de Fuca Ridge and the Cobb‐Eickelberg hot spot in the northeast Pacific Ocean that has erupted in 1998, 2011, and 2015. The 2015 eruption was recorded by a seven‐station seismic network in the southern part of the summit caldera that forms part of the Ocean Observatories Initiative Cabled Array. We utilize a data set of ~3,900 well‐recorded earthquakes from January 2015 to February 2017 and a three‐dimensional P wave velocity model obtained previously from active source data to conduct a joint inversion for three‐dimensional P and S wave velocities and hypocentral parameters. The resulting velocity models are used to relocate >76,000 earthquakes with ≥10 arrival times. The velocity models reveal a low‐velocity anomaly in the center of the southern caldera at depths less than ~2 km, which corresponds to the top of the magma chamber and is interpreted as a region that is intensely fractured by the cyclical deformation of the caldera. High velocities around the caldera rim are likely due to consolidated undeformed lava flows. Low VP/VS in the southern caldera is consistent with the presence of hydrothermal vapor. Low S wave velocities and high VP/VS in the northern caldera may indicate a region dominated by thin cracks caused by dike injection. The relocated earthquakes delineate outward‐dipping ring faults more clearly than previous studies and image a subvertical inward‐dipping fault within the network that connects to the east caldera wall and eruptive fissures.

Acoustic and in-situ observations of hydrothermal discharge at ASHES vent field

The Cabled Observatory Vent Imaging Sonar (COVIS) was installed on the Ocean Observatories Initiative’s Cabled Array observatory at ASHES hydrothermal vent field on Axial Seamount in July 2018. The acoustic backscatter data recorded by COVIS, in conjunction with in-situ temperature measurements, are used to investigate the temporal and spatial variations of hydrothermal venting within COVIS’s field-of-view. Areas in which diffuse hydrothermal flow is significant are identified by maps made using the standard deviation of the phase change between pings separated in time by fractions of 1 s. The results demonstrate significant influences of ocean tides and bottom currents on diffuse hydrothermal discharge. Comparison with local seismicity shows a small positive correlation between the areal coverage of diffuse hydrothermal discharge and the seismic activity in the vicinity of the vent field. This finding reveals an intimate connection between hydrothermal activity and geological processes during the dynamic period leading up to the next eruption of Axial Seamount. [Work sponsored by NSF.]

Thin Cable Fiber-Optic Hydrophone Array for Passive Acoustic Surveillance Applications

Fiber-optic interferometric sensing is a very attractive approach for creating lightweight, high-sensitive, and fully passive fiber-optic hydrophone arrays. In this paper, results of sea trials of the thin cable fiber-optic hydrophone array for passive acoustic surveillance applications are presented. The performed trials consisted of two parts: the first part was devoted to the estimation of the array acoustic performance and the second part included the direction of arrival (DOA) estimation of the moving acoustic source. The estimation of the array acoustic performance showed that the average measured pressure sensitivity of fiber-optic hydrophones increased as the acoustic frequency increased from -122 dB re rad/μPa at 20 Hz to -116 dB re rad/μPa at 495 Hz. The average minimum detectable pressure of hydrophones decreased from 78, 1 dB re μPa at 20 Hz to 28, 5 dB re 1 μPa at 495 Hz. Obtained values of the minimum detectable pressure were below the sea state zero noise level in the considered frequency range. The average dynamic range of fiber-optic hydrophones was above 120 dB at 495 Hz. The proper capability of the DOA estimation was successfully demonstrated using the motor boat as the moving acoustic source. Trajectories of the moving boat were obtained by using the beamscan DOA estimation algorithm with additional Kalman filtering. Obtained results demonstrated the great potential of using fiber-optic interferometric sensors for hydroacoustic surveillance applications. The presented results might be helpful for the implementation of extended fiber-optic hydroacoustic surveillance systems.

The Ocean Observatories Initiative

The Ocean Observatories Initiative (OOI) is an integrated network that enables scientific investigation of interlinked physical, chemical, biological and geological processes throughout the global ocean. With near real-time data delivery via a common Cyberinfrastructure, the OOI instruments two contrasting ocean systems at three scales. The Regional Cabled Array instruments a tectonic plate and overlying ocean in the northeast Pacific, providing a permanent electro-optical cable connecting multiple seafloor nodes that provide high power and bandwidth to seafloor sensors and moorings with instrumented wire crawlers, all with speed-of-light interactive capabilities. Coastal arrays include the Pioneer Array, a relocatable system currently quantifying the New England shelf-break front, and the Endurance Array, a fixed system off Washington and Oregon with connections to the Regional Cabled Array. The Global Arrays host deep-ocean moorings and gliders to provide interdisciplinary measurements of the water column, mesoscale variability, and air-sea fluxes at critical high latitude locations. The OOI has unique aspects relevant to the international ocean observing community. The OOI uses common sensor types, verification protocols, and data formats across multiple platform types in diverse oceanographic regimes. OOI observing is sustained, with initial deployment in 2013 and 25 years of operation planned. The OOI is distributed among sites selected for scientific relevance based on community input and linked by important oceanographic processes. Scientific highlights include real-time observations of a submarine volcanic eruption, time-series observations of methane bubble plumes from Southern Hydrate Ridge off Oregon, observations of anomalous low-salinity pulses off Oregon, discovery of new mechanisms for intrusions of the Gulf Stream onto the shelf in the Middle Atlantic Bight, documentation of deep winter convection in the Irminger Sea, and observations of extreme surface forcing at the most southerly surface mooring in the world ocean.

A numerical method for analyzing the influence of underwater vehicle flow field on dynamic behavior of towed sonar cable array

Simulations of the dynamic behavior of a sonar cable array towed by an underwater vehicle considering the influence of flow field disturbed by the underwater vehicle and its propeller are challenging tasks. In present paper, the strongly nonlinear towed sonar cable array is modeled by the Lumped-Mass method where the cable array is discretized into a series of massless springs and lumped-mass points. The drag force on the towed sonar cable array is obtained by calculating the drag force on each lumped-mass point considering the flow field of the underwater vehicle and its propeller, which is computed by CFD methods. The dynamic behavior of the towed sonar cable array is simulated by 4th Runge–Kutta method applying Newton's second law. Simulations of the three underwater vehicle motion modes including linear motions, turning motions and surfacing motions are performed. The results show that the numerical method proposed is reasonable, and the lateral deflection of the towed sonar cable array is related to the speeds and the motion modes of the underwater vehicle.

Hybrid Auxiliary Power Supply System for Offshore Wind Farm

Diesel Generators (DG) are commonly adopted to supply the critical auxiliary loads for Offshore Wind Farm (OWF) during islanding operation. To reduce fuel consumption, avoid over-sizing of DG, and further enable a smooth resynchronization to main grid, a hybrid Auxiliary Power Supply (APS) system is designed with a combination of DGs, Wind Turbine Generators (WTGs), and battery Energy Storage System (ESS). Different from the typical industrial solution, this hybrid APS system uses not only DGs, but also WTGs to supply part of the auxiliary load when there is wind blowing for reducing fuel consumption and the corresponding refuelling works; moreover, the wind turbine converters can provide reactive power for balancing the charging power from the cable array inside the OWF, so as to avoid the oversizing of DG itself. ESS are also introduced to further reduce the dependence on the DGs. With enough capacity of ESS, it is even possible to remove DGs while still be able to fulfil the requirement on auxiliary load supply during islanding mode.In this paper: firstly, the cost effectiveness of such hybrid APS is discussed via techno-economic analysis; secondly, two types of hybrid APSs with coordinated hierarchical control architectures are introduced, as well as the control strategy design for both centralized and distributed controllers; thirdly, simulation models are developed in MATLAB/Simulink, where two types of models are included. They are phasor-type model for centralized control strategy verification, and average-type model for distributed control strategy verification. The performance of hybrid APS models is validated under typical working scenarios, and the simulation results show that the control strategy has no high requirement on the communication speed between central controller and distributed controllers.

Circulation, hydrography, and transport over the summit of Axial Seamount, a deep volcano in the Northeast Pacific

AbstractA numerical model of ocean flow, hydrography, and transport is used to extrapolate observations of currents and hydrography and infer patterns of material flux in the deep ocean around Axial Seamount, a destination node of NSF's Ocean Observatories Initiative's Cabled Array. Using an inverse method, the model is made to approximate measured deep ocean flow around this site during a 35 day time period in the year 2002. The model is then used to extract month‐long mean patterns and examine smaller‐scale spatial and temporal variability around Axial. Like prior observations, model month‐long mean currents flow anticyclonically around the seamount's summit in toroidal form with maximum speeds at 1500 m depth of 10–11 cm/s. As a time mean, the temperature (salinity) anomaly distribution takes the form of a cold (briny) dome above the summit. Passive tracer material continually released at the location of the ASHES vent field exits the caldera primarily through its southern open end before filling the caldera. Once outside the caldera, the tracer circles the summit in clockwise fashion, fractionally reentering the caldera over lower walls at its north end, while gradually bleeding southwestward during the modeled time period into the ambient ocean. A second tracer release experiment using a source of only 2 day duration inside and near the CASM vent field at the northern end of the caldera suggests a residence time of the fluid at that locale of 8–9 days.

Array design considerations for exploitation of stable weakly dispersive modal pulses in the deep ocean

Modal pulses are broadband contributions to an acoustic wave field with fixed mode number. Stable weakly dispersive modal pulses (SWDMPs) are special modal pulses that are characterized by weak dispersion and weak scattering-induced broadening and are thus suitable for communications applications. This paper investigates, using numerical simulations, receiver array requirements for recovering information carried by SWDMPs under various signal-to-noise ratio conditions without performing channel equalization. Two groups of weakly dispersive modal pulses are common in typical mid-latitude deep ocean environments: the lowest order modes (typically modes 1–3 at 75Hz), and intermediate order modes whose waveguide invariant is near-zero (often around mode 20 at 75Hz). Information loss is quantified by the bit error rate (BER) of a recovered binary phase-coded signal. With fixed receiver depths, low BERs (less than 1%) are achieved at ranges up to 400km with three hydrophones for mode 1 with 90% probability and with 34 hydrophones for mode 20 with 80% probability. With optimal receiver depths, depending on propagation range, only a few, sometimes only two, hydrophones are often sufficient for low BERs, even with intermediate mode numbers. Full modal resolution is unnecessary to achieve low BERs. Thus, a flexible receiver array of autonomous vehicles can outperform a cabled array.

Inflation-predictable behavior and co-eruption deformation at Axial Seamount.

Deformation of the ground surface at active volcanoes provides information about magma movements at depth. Improved seafloor deformation measurements between 2011 and 2015 documented a fourfold increase in magma supply and confirmed that Axial Seamount's eruptive behavior is inflation-predictable, probably triggered by a critical level of magmatic pressure. A 2015 eruption was successfully forecast on the basis of this deformation pattern and marked the first time that deflation and tilt were captured in real time by a new seafloor cabled observatory, revealing the timing, location, and volume of eruption-related magma movements. Improved modeling of the deformation suggests a steeply dipping prolate-spheroid pressure source beneath the eastern caldera that is consistent with the location of the zone of highest melt within the subcaldera magma reservoir determined from multichannel seismic results.