Abstract One of the important issues on GPS‐acoustic (GPS‐A) observation for sea bottom positioning is how to address horizontal heterogeneity sound speed in oceans. This study presents an analysis method GPS‐A data presence a sloping structure. By applying this and revising scheme make full use existing data, we reevaluated postseismic deformations occurring ~1.5–5 years after 2011 Tohoku earthquake. The revised movements have more uniform directions rates between neighboring sites,...

We conducted deep‐sea magnetic measurements using autonomous underwater vehicles in the Bayonnaise knoll caldera, Izu‐Ogasawara island arc, which hosts large Hakurei hydrothermal field. improved conventional correction method applied for removing effect of vehicle magnetization, thus greatly enhancing precision resulting vector anomalies. The magnetization distribution obtained from anomaly data shows a ∼2 km wide belt high trending NNW‐SSE going through and low‐magnetization zone ∼300 m by...

Abstract We have developed a comprehensive inversion scheme to analyze traveltime data collected through GPS‐acoustic observations on campaign basis. Our method uses quantity called the “nadir total delay” (NTD), which is analogous zenith delay in Global Navigation Satellite Systems analyses, represent time variation of sound speed. The observation equation using NTD an approximated formulation. examine its applicable scope numerical experiments and demonstrate that approximation holds well...

Unlike basalt-hosted hydrothermal sites, characterized by a lack of magnetization, the magnetic signature ultramafic-hosted sites remains poorly known, despite their wide occurrence at slow-spreading ridges and strong mineral potential. The first high-resolution surveys such achieved deep-sea submersible on four Mid-Atlantic Ridge, reveal positive anomalies, therefore magnetization largest sites. This observation reflects presence mineralized zone beneath these stockwork, where several...

Abstract GNSS-A (combination of Global Navigation Satellite System and Acoustic ranging) observations have provided important geophysical results, typically based on static GNSS-Acoustic positioning methods. Recently, continuous using a moored buoy been attempted. Precise kinematic is essential for these approaches. In this study, we developed new method the extended Kalman filter (EKF). As observation model, parameters expressing underwater sound speed structure [nadir total delay (NTD)...

Near‐bottom magnetic measurements on board submersible Nautile were carried out the Mid‐Atlantic Ridge 21°40′N segment, and deep‐sea geomagnetic vector anomalies along 19 dive tracks obtained by applying processing method for shipboard three‐component magnetometer data. A forward modeling technique using short‐wavelength components of arising from local topography vertical motion was designed to estimate absolute magnetization intensity seafloor. In vicinity spreading axis a considerable...

We present a magnetic inversion method in the space domain using Akaike's Bayesian information criterion (ABIC). The horizontal variation of magnetization intensity is represented by linear combination bicubic B spline functions, and problem set to determine expansion coefficients. A prior constraint on roughness incorporated order suppress numerical instability. ABIC give us optimal weight relative requirement fitting observed data, which statistically determined from quality quantity data...

Abstract High‐resolution vector magnetic measurements were performed on five hydrothermal vent fields of the back‐arc spreading region southern Mariana Trough using Shinkai 6500 , a deep‐sea manned submersible. A new 3‐D forward scheme was applied that exploits surrounding bathymetry and varying altitudes submersible to estimate absolute crustal magnetization. The results revealed magnetic‐anomaly‐derived magnetizations show reasonable correlation with natural remanent rock samples collected...

Abstract Myojin Knoll caldera, one of the submarine silicic calderas lying on volcanic front northern Izu‐Ogasawara arc, has attracted increasing attention since discovery a large hydrothermal field called Sunrise deposit. Although numerous submersible surveys have been conducted in they not sufficiently explored areas to produce complete picture caldera and understand origin We comprehensive deep‐sea using an autonomous underwater vehicle obtained high‐resolution bathymetric magnetic data...

We assessed the positioning accuracy of GNSS-Acoustic (GNSS-A) measurement using a slackly moored buoy. A key feature real-time buoy-based GNSS-A is that must be performed via single ranging from an arbitrary observation position and encompassing drifting range In this study, slack-line mooring was employed to resist strong Kuroshio current up 5.5 knots in Nankai Trough. During year-long sea trial, buoy drifted within circle ~ 4000 m radius, which much larger than dimension seafloor...

The Rodriguez Triple Junction (RTJ) is a ridge‐ridge‐ridge triple junction connecting three mid‐ocean ridges in the Indian Ocean: Central Ridge (CIR), Southeast (SEIR), and Southwest (SWIR). We carried out three‐dimensional analyses of Sea Beam bathymetry, magnetic, gravity anomaly data covering an area about 200 km × 140 at obtained magnetization distribution Bouguer field. In magnetic inversion result some lineations CIR SEIR are recognized within SWIR valley, field shows little variation...

Abstract We report here results from a deep‐sea magnetic survey using an autonomous underwater vehicle over the Hakurei hydrothermal site, in middle Okinawa Trough. Magnetic inversion revealed that site is associated with well‐defined high‐magnetization zones distributed within broad low‐magnetization zone. Results rock measurements, performed on sulfide ore samples obtained by drilling, showed some possessed extremely high natural remanent magnetization (NRM) (as much as 6.8–953.0 A/m),...

Abstract The analysis of high‐resolution vector magnetic data acquired by deep‐sea submersibles (DSSs) requires the development specific approaches adapted to their uneven tracks. We present a method that takes advantage (1) varying altitude DSS above seafloor and (2) multibeam bathymetric separately, at higher altitude, an Autonomous Underwater Vehicle, estimate absolute magnetization intensity polarity shallow subseafloor along path. apply this collected Nautile on small active...

The GNSS-acoustic technique is a geodetic method for oceanic areas that combines GNSS positioning of sea-surface platform and acoustic ranging seafloor stations. Its accuracy typically few several centimeters the horizontal vertical positions, respectively. For further enhancement, we examined errors in travel time, most fundamental data ranging. reference signal used our observations series sinusoidal waves modulated by binary phase-shift keying with maximal length sequence whose...

Abstract We collected deep‐sea multibeam, side scan, and subbottom profiler data using an autonomous underwater vehicle at the Bayonnaise knoll, a submarine caldera located in rift zone of Izu‐Ogasawara arc. aimed to reveal topographic geological features origin hydrothermal field called Hakurei site caldera. performed seafloor classification by textural analysis calibrated side‐scan sonar data, which provided effective means understand geology highlight potential areas constructions. The...

Realtime observations of vertical/horizontal seafloor movements and sea surface height associated with a huge earthquake are crucial for immediate recognition its causal fault rupture, so that tsunami early warning can be issued also the risk subsequent ruptures evaluated. For this purpose, we developed an offshore monitoring system using moored buoy platform to measure, in realtime, three observables mentioned above operated it on trial basis year. While operating system, GPS-acoustic...

2008年3月および10月に，伊豆・小笠原弧の背弧リフト東縁部に位置するベヨネーズ海丘カルデラにおいて東京大学生産技術研究所が開発したAUV（Autonomous Underwater Vehicle: 自律型海中ロボット）r2D4...

We developed a method for mapping the magnetic structure of absolute magnetization on seafloor using three-dimensional forward modeling technique and near-bottom vector data. constrained spatial scale hydrothermal alteration zones in back-arc spreading axis Southern Mariana Trough. The signatures are characterized by low similar to that mid-ocean ridge vent sites.

A new hydrothermal vent site in the southern Mariana Trough has been discovered using acoustic and magnetic surveys. Two stage surveys by autonomous underwater vehicle (AUV) Urashima (Japan Agency for Marine-Earth Science Technology, JAMSTEC) manned submersible Shinkai 6500 (JAMSTEC) were conducted 2009 2010, respectively. In first stage, we detected a clear magnetization low that extends from previously known site, Pika vector magnetometer attached to AUV. The signals suggest presence of...