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National Academies of Sciences, Engineering, Medicine.  2017.  Sustaining ocean observations to understand future changes in earth’s climate. :150., Washington, DC: The National Academies Press   10.17226/24919   Abstract

The ocean is an integral component of the Earth’s climate system. It covers about 70% of the Earth’s surface and acts as its primary reservoir of heat and carbon, absorbing over 90% of the surplus heat and about 30% of the carbon dioxide associated with human activities, and receiving close to 100% of fresh water lost from land ice. With the accumulation of greenhouse gases in the atmosphere, notably carbon dioxide from fossil fuel combustion, the Earth’s climate is now changing more rapidly than at any time since the advent of human societies. Society will increasingly face complex decisions about how to mitigate the adverse impacts of climate change such as droughts, sea-level rise, ocean acidification, species loss, changes to growing seasons, and stronger and possibly more frequent storms. Observations play a foundational role in documenting the state and variability of components of the climate system and facilitating climate prediction and scenario development. Regular and consistent collection of ocean observations over decades to centuries would monitor the Earth’s main reservoirs of heat, carbon dioxide, and water and provides a critical record of long-term change and variability over multiple time scales. Sustained high-quality observations are also needed to test and improve climate models, which provide insights into the future climate system. Sustaining Ocean Observations to Understand Future Changes in Earth’s Climate considers processes for identifying priority ocean observations that will improve understanding of the Earth’s climate processes, and the challenges associated with sustaining these observations over long timeframes.

Berger, J, Laske G, Babcock J, Orcutt J.  2016.  An ocean bottom seismic observatory with near real-time telemetry. Earth and Space Science.   10.1002/2015EA000137   Abstract

We describe a new technology that can provide near real-time telemetry of sensor data from the ocean bottom without a moored buoy or a cable to shore. The breakthrough technology that makes this system possible is an autonomous surface vehicle called a Wave Glider developed by Liquid Robotics, Inc. of Sunnyvale, CA., which harvests wave and solar energy for motive and electrical power. We present results from several deployments of a prototype system that demonstrate the feasibility of this concept. We also demonstrated that a wave glider could tow a suitably designed ocean bottom package with acceptable loss of speed. With further development such a system could be deployed autonomously and provide real-time telemetry of data from seafloor sensors. This article is protected by copyright. All rights reserved.

Gallagher, J, Orcutt J, Simpson P, Wright D, Pearlman J, Raymond L.  2015.  Facilitating open exchange of data and information. Earth Science Informatics. 8:721-739.   10.1007/s12145-014-0202-2   AbstractWebsite

By broad consensus, Open Data presents great value. However, beyond that simple statement, there are a number of complex, and sometimes contentious, issues that the science community must address. In this review, we examine the current state of the core issues of Open Data with the unique perspective and use cases of the ocean science community: interoperability; discovery and access; quality and fitness for purpose; and sustainability. The topics of Governance and Data Publication are also examined in detail. Each of the areas covered are, by themselves, complex and the approaches to the issues under consideration are often at odds with each other. Any comprehensive policy on Open Data will require compromises that are best resolved by broad community input. In the final section of the review, we provide recommendations that serve as a starting point for these discussions.

Mikhalevsky, PN, Sagen H, Worcester PF, Baggeroer AB, Orcutt J, Moore SE, Lee CM, Vigness-Raposa KJ, Freitag L, Arrott M, Atakan K, Beszczynska-Moeller A, Duda TF, Dushaw BD, Gascard JC, Gavrilov AN, Keers H, Morozov AK, Munk WH, Rixen M, Sandven S, Skarsoulis E, Stafford KM, Vernon F, Yuen MY.  2015.  Multipurpose Acoustic Networks in the Integrated Arctic Ocean Observing System. Arctic. 68:11-27. AbstractWebsite

The dramatic reduction of sea ice in the Arctic Ocean will increase human activities in the coming years. This activity will be driven by increased demand for energy and the marine resources of an Arctic Ocean accessible to ships. Oil and gas exploration, fisheries, mineral extraction, marine transportation, research and development, tourism, and search and rescue will increase the pressure on the vulnerable Arctic environment. Technologies that allow synoptic in situ observations year-round are needed to monitor and forecast changes in the Arctic atmosphere-ice-ocean system at daily, seasonal, annual, and decadal scales. These data can inform and enable both sustainable development and enforcement of international Arctic agreements and treaties, while protecting this critical environment. In this paper, we discuss multipurpose acoustic networks, including subsea cable components, in the Arctic. These networks provide communication, power, underwater, and under-ice navigation, passive monitoring of ambient sound (ice, seismic, biologic, and anthropogenic), and acoustic remote sensing (tomography and thermometry), supporting and complementing data collection from platforms, moorings, and vehicles. We support the development and implementation of regional to basin-wide acoustic networks as an integral component of a multidisciplinary in situ Arctic Ocean observatory.

Wolfe, CJ, Solomon SC, Laske G, Collins JA, Detrick RS, Orcutt JA, Bercovici D, Hauri EH.  2011.  Mantle P-wave velocity structure beneath the Hawaiian hotspot. Earth and Planetary Science Letters. 303:267-280.   10.1016/j.epsl.2011.01.004   AbstractWebsite

Three-dimensional images of P-wave velocity structure beneath the Hawaiian Islands, obtained from a network of seafloor and land seismometers, show an upper-mantle low-velocity anomaly that is elongated in the direction of the island chain and surrounded by a high-velocity anomaly in the shallow upper mantle that is parabolic in map view. Low velocities continue downward to the mantle tansition zone between 410 and 660 km depth and extend into the topmost lower mantle, although the resolution of lower mantle structure from this data set is limited. Comparisons of inversions with separate data sets at different frequencies suggest that contamination by water reverberations is not markedly biasing the P-wave imaging of mantle structure. Many aspects of the P-wave images are consistent with independent tomographic images of S-wave velocity in the region, but there are some differences in upper mantle structure between P-wave and S-wave velocities. Inversions without station terms show a southwestward shift in the location cif lowest P-wave velocities in the uppermost mantle relative to the pattern for shear waves, and inversions with station terms show differences between P-wave and S-wave velocity heterogeneity in the shallow upper mantle beneath and immediately east of the island of Hawaii. Nonetheless, the combined data sets are in general agreement with the hypothesis that the Hawaiian hotspot is the result of an upwelling, high-temperature plume. The broad upper-mantle low-velocity region beneath the Hawaiian Islands may reflect the diverging "pancake" at the top of the upwelling zone; the surrounding region of high velocities could represent a downwelling curtain; and the low-velocity anomalies southeast of Hawaii in the transition zone and topmost lower mantle are consistent with predictions of plume tilt. (C) 2011 Elsevier B.V. All rights reserved.

Laske, G, Markee A, Orcutt JA, Wolfe CJ, Collins JA, Solomon SC, Detrick RS, Bercovici D, Hauri EH.  2011.  Asymmetric shallow mantle structure beneath the Hawaiian Swell-evidence from Rayleigh waves recorded by the PLUME network. Geophysical Journal International. 187:1725-1742.   10.1111/j.1365-246X.2011.05238.x   AbstractWebsite

We present models of the 3-D shear velocity structure of the lithosphere and asthenosphere beneath the Hawaiian hotspot and surrounding region. The models are derived from long-period Rayleigh-wave phase velocities that were obtained from the analysis of seismic recordings collected during two year-long deployments for the Hawaiian Plume-Lithosphere Undersea Mantle Experiment. For this experiment, broad-band seismic sensors were deployed at nearly 70 seafloor sites as well as 10 sites on the Hawaiian Islands. Our seismic images result from a two-step inversion of path-averaged dispersion curves using the two-station method. The images reveal an asymmetry in shear velocity structure with respect to the island chain, most notably in the lower lithosphere at depths of 60 km and greater, and in the asthenosphere. An elongated, 100-km-wide and 300-km-long low-velocity anomaly reaches to depths of at least 140 km. At depths of 60 km and shallower, the lowest velocities are found near the northern end of the island of Hawaii. No major velocity anomalies are found to the south or southeast of Hawaii, at any depth. The low-velocity anomaly in the asthenosphere is consistent with an excess temperature of 200-250 degrees C and partial melt at the level of a few percent by volume, if we assume that compositional variations as a result of melt extraction play a minor role. We also image small-scale low-velocity anomalies within the lithosphere that may be associated with the volcanic fields surrounding the Hawaiian Islands.

Cowles, T, Delaney J, Orcutt J, Weller R.  2010.  The Ocean Observatories Initiative: Sustained Ocean Observing Across a Range of Spatial Scales. Marine Technology Society Journal. 44:54-64. AbstractWebsite

The Ocean Observatory Initiative of the U.S. National Science Foundation is working to advance the ocean sciences by developing the infrastructure for sustained ocean observations at key coastal and open ocean locations. The effort comprises two coastal arrays, four global arrays in the deep ocean, a cabled observatory over the Juan de Fuca tectonic plate, and a sophisticated cyberinfrastructure. The initial installations will be completed by 2015, and 25 years of operation will follow. This article provides an overview of the Ocean Observatory Initiative, followed by more detail about the coastal, regional, and global components. Science drivers are reviewed first. Then, the platforms to be deployed at each site, both moorings and mobile platforms, are described, as are the planned, multidisciplinary core sensors. All data will be freely available.

Schofield, O, Kohut J, Glenn S, Morell J, Capella J, Corredor J, Orcutt J, Arrott M, Krueger I, Meisinger M, Peach C, Vernon F, Chave A, Chao Y, Chien S, Thompson D, Brown W, Oliver M, Boicourt W.  2010.  A Regional Slocum Glider Network in the Mid-Atlantic Bight Leverages Broad Community Engagement. Marine Technology Society Journal. 44:185-195. AbstractWebsite

Autonomous underwater gliders have proven to be a cost-effective technology for measuring the 3-D ocean and now represent a critical component during the design and implementation of the Mid-Atlantic Regional Ocean Observing System (MARCOOS), a Region of the U.S. Integrated Ocean Observing System. The gliders have been conducting regional surveys of the Mid-Atlantic (MA) Bight, and during the 3 years of MARCOOS, the glider fleet has conducted 22 missions spanning 10,867 km and collecting 62,824 vertical profiles of data. In addition to collecting regional data, the gliders have facilitated collaboration for partners outside of MARCOOS. The existence of the MA glider observatory provided a unique test bed for cyber-infrastructure tools being developed as part of the National Science Foundation's Ocean Observatory Initiative. This effort allowed the Ocean Observatory Initiative software to integrate the MARCOOS assets and provided a successful demonstration of an ocean sensor net. The hands-on experience of the MA glider technicians supported training and provided assistance of collaborators within the Caribbean Regional Association, also a region of the U.S. Integrated Ocean Observing System, to assess the efficacy of gliders to resolve internal waves. Finally, the glider fleet has enabled sensor development and testing in a cost-effective manner. Generally, new sensors were tested within the MARCOOS domain before they were deployed in more extreme locations throughout the world's oceans. On the basis of this experience, the goal of the MARCOOS glider team will be to expand the MA network in coming years. The potential of how an expanded network of gliders might serve national needs was illustrated during the 2010 Macondo Gulf of Mexico oil spill, where gliders from many institutions collected subsurface mesoscale data to support regional models and oil response planning. The experience gained over the last 5 years suggests that it is time to develop a national glider network.

Holmes, RC, Tolstoy M, Harding AJ, Orcutt JA, Morgan JP.  2010.  Australian Antarctic Discordance as a simple mantle boundary. Geophysical Research Letters. 37   10.1029/2010gl042621   AbstractWebsite

Several complex models require unique mantle conditions to explain the Australian Antarctic Discordance (AAD), an unusually deep and rugged section of the Southeast Indian Ridge (SEIR) between similar to 120 degrees-128 degrees E. Seismic evidence suggests the AAD is instead the manifestation of two contrasting mantle domains converging along its eastern edge. Variations in axial morphology and flanking topographic relief along the SEIR arise as ridge segments to the west (Indian mantle) grade into a cooler melting regime while those to the east (Pacific mantle) are more magmatically robust. Seismic refraction data show crustal thickness decreases from the west into the AAD at a rate of 0.1 km/100 km, then rapidly increases from 4.8 +/- 0.4 km to 7.3 +/- 0.2 km across the eastern border. The AAD thus appears to be the terminal end of a long-wavelength reduction in melt supply at what may be the simplest global example of a mantle boundary. Citation: Holmes, R. C., M. Tolstoy, A. J. Harding, J. A. Orcutt, and J. P. Morgan (2010), Australian Antarctic Discordance as a simple mantle boundary, Geophys. Res. Lett., 37, L09309, doi: 10.1029/2010GL042621.

Wolfe, CJ, Solomon SC, Laske G, Collins JA, Detrick RS, Orcutt JA, Bercovici D, Hauri EH.  2009.  Mantle Shear-Wave Velocity Structure Beneath the Hawaiian Hot Spot. Science. 326:1388-1390.   10.1126/science.1180165   AbstractWebsite

Defining the mantle structure that lies beneath hot spots is important for revealing their depth of origin. Three-dimensional images of shear-wave velocity beneath the Hawaiian Islands, obtained from a network of sea-floor and land seismometers, show an upper-mantle low-velocity anomaly that is elongated in the direction of the island chain and surrounded by a parabola-shaped high-velocity anomaly. Low velocities continue downward to the mantle transition zone between 410 and 660 kilometers depth, a result that is in agreement with prior observations of transition-zone thinning. The inclusion of SKS observations extends the resolution downward to a depth of 1500 kilometers and reveals a several-hundred-kilometer-wide region of low velocities beneath and southeast of Hawaii. These images suggest that the Hawaiian hot spot is the result of an upwelling high-temperature plume from the lower mantle.

Santelli, CM, Orcutt BN, Banning E, Bach W, Moyer CL, Sogin ML, Staudigel H, Edwards KJ.  2008.  Abundance and diversity of microbial life in ocean crust. Nature. 453:653-U7.   10.1038/nature06899   AbstractWebsite

Oceanic lithosphere exposed at the sea floor undergoes seawater rock alteration reactions involving the oxidation and hydration of glassy basalt. Basalt alteration reactions are theoretically capable of supplying sufficient energy for chemolithoautotrophic growth(1). Such reactions have been shown to generate microbial biomass in the laboratory(2), but field- based support for the existence of microbes that are supported by basalt alteration is lacking. Here, using quantitative polymerase chain reaction, in situ hybridization and microscopy, we demonstrate that prokaryotic cell abundances on seafloor- exposed basalts are 3 - 4 orders of magnitude greater than in overlying deep sea water. Phylogenetic analyses of basaltic lavas from the East Pacific Rise ( 9 degrees N) and around Hawaii reveal that the basalt- hosted biosphere harbours high bacterial community richness and that community membership is shared between these sites. We hypothesize that alteration reactions fuel chemolithoautotrophic microorganisms, which constitute a trophic base of the basalt habitat, with important implications for deep- sea carbon cycling and chemical exchange between basalt and sea water.

Orcutt, JA.  2007.  Global Ocean Observatories. Law, science & ocean management. ( Nordquist MH, Long R, Heidar TH, Moore JN, Eds.).:295-296., Leiden [etc.]: Nijhoff Abstract
Laske, G, Phipps Morgan J, Orcutt JA.  2007.  The Hawaiian SWELL pilot experiment; evidence for lithosphere rejuvenation from ocean bottom surface wave data. GSA Special Paper. 430:209-233.   10.1130/2007.2430(11)   Abstract

During the roughly year-long Seismic Wave Exploration in the Lower Lithosphere (SWELL) pilot experiment in 1997/1998, eight ocean bottom instruments deployed to the southwest of the Hawaiian Islands recorded teleseismic Rayleigh waves with periods between 15 and 70 s. Such data are capable of resolving structural variations in the oceanic lithosphere and upper asthenosphere and therefore help understand the mechanism that supports the Hawaiian Swell relief. The pilot experiment was a technical as well as a scientific feasibility study and consisted of a hexagonal array of Scripps Low-Cost Hardware for Earth Applications and Physical Oceanography (L-CHEAPO) instruments using differential pressure sensors. The analysis of eighty-four earthquakes provided numerous high-precision phase velocity curves over an un-precedentedly wide period range. We find a rather uniform (unaltered) lid at the top of the lithosphere that is underlain by a strongly heterogeneous lower lithosphere and upper asthenosphere. Strong slow anomalies appear within ∼300 km of the island chain and indicate that the lithosphere has most likely been altered by the same process that causes the Hawaiian volcanism. The anomalies increase with depth and reach well into the asthenosphere, suggesting a sublithospheric dynamic source for the swell relief. The imaged velocity variations are consistent with thermal rejuvenation, but our array does not appear to have covered the melt-generating region of the Hawaiian hotspot.

Taesombut, N, Uyeda F, Chien AA, Smarr L, DeFanti TA, Papadopoulos P, Leigh J, Ellisman M, Orcutt J.  2006.  The OptIPuter: High-performance, QoS-guaranteed network service for emerging e-science applications. IEEE Communications Magazine. 44:38-45.   10.1109/mcom.2006.1637945   AbstractWebsite

Emerging large-scale scientific applications have a critical need for high bandwidth and predictable-performance network service. The OptIPuter project is pioneering a radical new type of distributed application paradigm that exploits dedicated optical circuits to tightly couple geographically dispersed resources. These private optical paths are set up on demand and combined with end resources to form a distributed virtual computer (DVC). The DVC provides high-quality dedicated network service to applications. In this article we compare the OptIPuter's approach (DVC), which exploits network resources to deliver higher-quality network services, to several alternative service models (intelligent network and asynchronous file transfer). Our simulations show that there are significant differences among the models in their utilization of resources and delivered application services. Key takeaways include that the OptIPuter approach provides applications with superior network service (as needed by emerging e-science applications and performance-critical distributed applications), at an expense in network resource consumption. The other approaches use fewer network resources, but provide lower-quality application service.

Singh, SC, Harding AJ, Kent GM, Sinha MC, Combier V, Bazin S, Tong CH, Pye JW, Barton PJ, Hobbs RW, White RS, Orcutt JA.  2006.  Seismic reflection images of the Moho underlying melt sills at the East Pacific Rise. Nature. 442:287-290.   10.1038/nature04939   AbstractWebsite

The determination of melt distribution in the crust and the nature of the crust - mantle boundary ( the 'Moho') is fundamental to the understanding of crustal accretion processes at oceanic spreading centres. Upper-crustal magma chambers have been imaged beneath fast- and intermediate-spreading centres(1-4) but it has been difficult to image structures beneath these magma sills. Using three-dimensional seismic reflection images, here we report the presence of Moho reflections beneath a crustal magma chamber at the 9 degrees 03' N overlapping spreading centre, East Pacific Rise. Our observations highlight the formation of the Moho at zero-aged crust. Over a distance of less than 7 km along the ridge crest, a rapid increase in two-way travel time of seismic waves between the magma chamber and Moho reflections is observed, which we suggest is due to a melt anomaly in the lower crust. The amplitude versus offset variation of reflections from the magma chamber shows a coincident region of higher melt fraction overlying this anomalous region, supporting the conclusion of additional melt at depth.

Taesombut, N, Wu X, Chien AA, Nayak A, Smith B, Kilb D, Im T, Samilo D, Kent G, Orcutt J.  2006.  Collaborative data visualization for Earth Sciences with the OptIPuter. Future Generation Computer Systems. 22:955-963.   AbstractWebsite

Collaborative visualization of large-scale datasets across geographically distributed sites is becoming increasingly important for Earth Sciences. Not only does it enhance our understanding of the geological systems, but also enables near-real-time scientific data acquisition and exploration across distant locations. While such a collaborative environment is feasible with advanced optical networks and resource sharing in the form of Grid, many technical challenges remain: (1) on-demand discovery, selection and configuration of supporting end and network resources; (2) construction of applications on heterogeneous, distributed environments; and (3) use of novel exotic transport protocols to achieve high performance. To address these issues, we describe the multi-layered OptIPuter middleware technologies, including simple resource abstractions, dynamic network provisioning, and novel data transport services. In this paper, we present an evaluation of the first integrated prototype of the OptIPuter system software recently demonstrated at iGrid 2005, which successfully supports real-time collaborative visualizations of 3D multi-gigabyte earth science datasets.

Suyehiro, K, Montagner JP, Stephen RA, Araki E, Kanazawa T, Orcutt J, Romanowicz B, Shinohara M.  2006.  Ocean Seismic Observatories. Oceanography. 19:144-149.   10.5670/oceanog.2006.12   Abstract
Berger, J, Orcutt J, Vernon F.  2005.  HiSeasNet: Providing Internet to the UNOLS fleet. Sea Technology. 46:17-20. AbstractWebsite
Rajasekar, A, Lu S, Moore R, Vernon F, Orcutt J, Lindquist K.  2005.  Accessing sensor data using meta data: a virtual object ring buffer framework. Proceedings of the 2nd international workshop on Data management for sensor networks. :35-42., Trondheim, Norway: ACM   10.1145/1080885.1080892   Abstract
Tong, CH, Lana C, White RS, Warner MR, Barton PJ, Bazin S, Harding AJ, Hobbs RW, Kent GM, Orcutt JA, Pye JW, Singh SC, Sinha MC.  2005.  Subsurface tectonic structure between overlapping mid-ocean ridge segments. Geology. 33:409-412.   10.1130/g21245.1   AbstractWebsite

Our results from seismic anisotropy analyses reveal for the first time the complex spatial variability of the characteristics of subsurface tectonic structures associated with ridge propagation. The significance lies in the fact that these variations are found at a locality with few lineaments or fissures at seafloor level. The overlap region between mid-ocean ridge segments at 9 degrees N on the East Pacific Rise is characterized by aligned cracks that are structurally more closely related to the propagating-ridge segment. These aligned cracks, which are approximately parallel to the ridge segments, provide conclusive observational evidence for establishing the nontransform nature of overlapping spreading centers, especially those with overlap basins covered by volcanic edifices. The aligned cracks of the 9 degrees 03'N overlapping spreading center are more similar to the ridge-parallel lineaments observed between overlapping axial-summit collapse troughs than those found at larger overlapping spreading centers. Our results therefore suggest that the lithospheric deformation between overlapping ridge segments depends on ridge offset and that this dependency may be thermally related.

Sutherland, FH, Vernon FL, Orcutt JA, Collins JA, Stephen RA.  2004.  Results from OSNPE: Improved teleseismic earthquake detection at the seafloor. Bulletin of the Seismological Society of America. 94:1868-1878.   10.1785/012003088   AbstractWebsite

Earthquake data from three ocean seismic network (OSN) sensors, located (1) on the seafloor, (2) buried in seafloor sediments and (3) in a borehole, together with those from Hawaiian Island stations, were compared by calculating threshold-detection magnitudes for P-, S-, Rayleigh-, and Love-wave arrivals. Our results show that the borehole seismometer had noise levels similar to those of the Island stations and produced high-quality high- and low-frequency body- and surface-wave data. Shallow burial of the seismometer in the sediments had no effect on higher frequencies but significantly reduced low-frequency noise levels so that data for S and Rayleigh waves were of high quality. In fact, the buried seismometer was characterized by the lowest noise levels at very low frequencies (<20 mHz; Collins et al., 2001). The ocean-floor seismometer was consistently noisy, and the data produced were of lower quality. Both observed magnitudes and calculated threshold magnitudes were lower by more than an order of magnitude than those observed in previous studies. Results for short-period body waves at the borehole instrument in particular were much better than those that were previously found for any ocean-bottom recording.

Blackman, DK, de Groot-Hedlin C, Harben P, Sauter A, Orcutt JA.  2004.  Testing low/very low frequency acoustic sources for basin-wide propagation in the Indian Ocean. Journal of the Acoustical Society of America. 116:2057-2066.   10.1121/1.1786711   AbstractWebsite

Low/very low frequency acoustic signals were transmitted to distant receivers in the Indian Ocean. The aim was to test methods for characterizing the hydroacoustic capability of the International Monitoring System (IMS) that discriminates for nuclear tests in the region. Several acoustic sources were deployed between Seychelles and Fremantle, Australia, and the IMS receivers comprised a network of hydrophones off Diego Garcia and Australia. Two of the three acoustic sources tested produced basin-scale propagation of impulsive signals. Single glass spheres imploded within the sound channel produced a clear signal at frequencies above similar to40 Hz, at ranges of hundreds to a thousand kilometers. Five-sphere glass implosions were recorded at ranges up to 4400 km. Near-sea surface shots from a large airgun array were recorded in several cases at ranges of hundreds to thousands of kilometers, the frequency of the highest signal-to-noise ratio arrivals varied within the 5-100 Hz band. High background noise level was a key factor at IMS stations that did not detect the airgun signals in the 5-15 Hz band. In a few cases, details of bathymetric features that are not well represented in the digital elevation model contributed to unexpected variation in relative signal levels between IMS stations. (C) 2004 Acoustical Society of America.

Tong, CH, White RS, Warner MR, Barton PJ, Bazin S, Harding AJ, Hobbs RW, Kent GM, Orcutt JA, Pye JW, Singh SC, Sinha MC.  2004.  Effects of tectonism and magmatism on crack structure in oceanic crust; a seismic anisotropy study. Geology. 32:25-28.   10.1130/g19962.1   AbstractWebsite

We analyzed 25,675 traveltime residuals from a three-dimensional seismic tomographic inversion to investigate crack-induced seismic anisotropy in the upper oceanic crust. The study covered two regions with contrasting levels of magmatic activity on the western limb of the 9 degrees N overlapping spreading center on the East Pacific Rise. The level of anisotropy gradually decreases with depth in the magmatically and hydrothermally active ridge region. In contrast, we observed a highly variable anisotropic structure in the magmatically and hydrothermally less active tip region at the end of the dying ridge segment: a weakly anisotropic layer beneath strongly anisotropic extrusive volcanic rocks is likely to be the result of relatively shallow cracks closed by hydrothermal precipitation. Strongly anisotropic dikes with inferred narrow and water-saturated cracks provide important along-axis pathways for the circulation of hydrothermal fluids beneath the shallow cracks in the less magmatically active regions. Furthermore, a significant clockwise rotation (20 degrees -30 degrees ) of fast directions occurs in both regions with increasing depth. Such a rotation provides evidence that the geometry of the underlying crack structure of the western limb is significantly different from that defined by the bathymetric ridge crest.

Tong, CH, Barton PJ, White RS, Sinha MC, Singh SC, Pye JW, Hobbs RW, Bazin S, Harding AJ, Kent GM, Orcutt JA.  2003.  Influence of enhanced melt supply on upper crustal structure at a mid-ocean ridge discontinuity: A three-dimensional seismic tomographic study of 9 degrees N East Pacific Rise. Journal of Geophysical Research-Solid Earth. 108   10.1029/2002jb002163   AbstractWebsite

[1] We present a three-dimensional upper crustal model of the 9degrees03'N overlapping spreading center (OSC) on the East Pacific Rise that assists in understanding the relationship between melt sills and upper crustal structure at a ridge discontinuity with enhanced melt supply at crustal levels. Our P wave velocity model obtained from tomographic inversion of similar to 70,000 crustal first arrival travel times suggests that the geometry of extrusive emplacement are significantly different beneath the overlapping spreading limbs. Extrusive volcanic rocks above the western melt sill are inferred to be thin ( similar to 250 m). More extensive accumulation of extrusives is inferred to the west than to the east of the western melt sill. The extrusive layer inferred above the eastern melt sill thickens from similar to 350 ( at the neovolcanic axis) to 550 m ( to the west of the melt sill). Volcanic construction is likely to be significant in the formation of ridge crest morphology at the OSC, particularly at the tip of the eastern limb. On the basis of our interpretation of the velocity model, we propose that enhanced magma supply at crustal levels at the OSC may provide an effective mechanism for the migration of ridge discontinuities. This "dynamic magma supply model'' may explain the commonly observed nonsteady migration pattern of ridge discontinuities by attributing this to the temporal fluctuations in melt availability to the overlapping spreading limbs.

Newman, HB, Ellisman MH, Orcutt JA.  2003.  Data-intensive e-science - Frontier research. Communications of the ACM. 46:67-75. AbstractWebsite