Marine Geophysics Research Articles

Design and construction of system for marine geophysics data sharing based on WebGIS

A browser/server system has been developed for the purpose of marine geophysical data sharing based on WebGIS technology, which uses MapServer open source system and ORACLE Database Management System. The main steps during development, including system design and implementation, are discussed in this article. The system can provide convenient, efficient, and interactive marine geophysical information sharing and visualization services through Internet or Intranet to improve data exchange and utilization.

Introduction to the TAIGER special issue of Marine Geophysical Research

Introduction to the TAIGER special issue of Marine Geophysical Research

Stratigraphic and structural setting of the Ischia volcanic complex (Naples Bay, Southern Italy) revealed by submarine seismic reflection data

High-resolution seismic reflection profiles (Sparker Multitip) offshore southern Ischia Island (Naples Bay) are presented, together with a geological interpretation of their volcanic, structural and sedimentary features. In this frame, new seismo-stratigraphic evidences on buried volcanic structures and overlying Quaternary deposits of the southeastern offshore of the Ischia Island are discussed to highlight their implications on the marine geophysics and volcanology. The Ischia Bank is a large and flat relic volcanic edifice with steep slopes, merging on the continental shelf. The age of this monogenic volcano is unknown, lacking a direct datation of its basement. It represents the eruptive center of the pyroclastic fall cropping out onshore in the eastern sectors of the island, ranging in age from 8 to 6 ky bp. In the eastern Ischia offshore relic volcanic edifices, mostly formed by hialoclastites, have been investigated through high-resolution seismics. They represent remnants of hydro-magmatic volcanic vents and suggest a subaqueous emplacement. Regional seismic sections in the southeastern Ischia offshore, across buried volcanic structures, are finally presented and discussed.

Distributed Mobile Sensor Networks for Hazardous Applications

1Research Department for Underwater Acoustics and Marine Geophysics, Bundeswehr Technical Centre for Ships and Naval Weapons, Naval Technology and Research (WTD 71), Klausdorfer Weg 2, 24148 Kiel, Germany 2Navy Center for Applied Research in Artificial Intelligence, Naval Research Laboratory, 4555 Overlook Avenue S.W., Washington, DC 20375, USA 3Acoustic Research Laboratory, National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077 4 Systems Technology Department, NATO Undersea Research Centre (NURC), Viale S. Bartolomeo 400, 19126 La Spezia, Italy

High‐resolution backprojection at regional distance: Application to the HaitiM7.0 earthquake and comparisons with finite source studies

A catastrophicMw7 earthquake ruptured on 12 January 2010 on a complex fault system near Port‐au‐Prince, Haiti. Offshore rupture is suggested by aftershock locations and marine geophysics studies, but its extent remains difficult to define using geodetic and teleseismic observations. Here we perform the multitaper multiple signal classification (MUSIC) analysis, a high‐resolution array technique, at regional distance with recordings from the Venezuela National Seismic Network to resolve high‐frequency (about 0.4 Hz) aspects of the earthquake process. Our results indicate westward rupture with two subevents, roughly 35 km apart. In comparison, a lower‐frequency finite source inversion with fault geometry based on new geologic and aftershock data shows two slip patches with centroids 21 km apart. Apparent source time functions from USArray further constrain the intersubevent time delay, implying a rupture speed of 3.3 km/s. The tips of the slip zones coincide with subevents imaged by backprojections. The different subevent locations found by backprojection and source inversion suggest spatial complementarity between high‐ and low‐frequency source radiation consistent with high‐frequency radiation originating from rupture arrest phases at the edges of main slip areas. The centroid moment tensor (CMT) solution and a geodetic‐only inversion have similar moment, indicating most of the moment released is captured by geodetic observations and no additional rupture is required beyond where it is imaged in our preferred model. Our results demonstrate the contribution of backprojections of regional seismic array data for earthquakes down toM≈ 7, especially when incomplete coverage of seismic and geodetic data implies large uncertainties in source inversions.

Ocean Bottom Seismometer: Design and Test of a Measurement System for Marine Seismology

The Ocean Bottom Seismometer (OBS) is a key instrument for the geophysical study of sea sub-bottom layers. At present, more reliable autonomous instruments capable of recording underwater for long periods of time and therefore handling large data storage are needed. This paper presents a new Ocean Bottom Seismometer designed to be used in long duration seismic surveys. Power consumption and noise level of the acquisition system are the key points to optimize the autonomy and the data quality. To achieve our goals, a new low power data logger with high resolution and Signal–to-Noise Ratio (SNR) based on Compact Flash memory card is designed to enable continuous data acquisition. The equipment represents the achievement of joint work from different scientific and technological disciplines as electronics, mechanics, acoustics, communications, information technology, marine geophysics, etc. This easy to handle and sophisticated equipment allows the recording of useful controlled source and passive seismic data, as well as other time varying data, with multiple applications in marine environment research. We have been working on a series of prototypes for ten years to improve many of the aspects that make the equipment easy to handle and useful to work in deep-water areas. Ocean Bottom Seismometers (OBS) have received growing attention from the geoscience community during the last forty years. OBS sensors recording motion of the ocean floor hold key information in order to study offshore seismicity and to explore the Earth’s crust. In a seismic survey, a series of OBSs are placed on the seabed of the area under study, where they record either natural seismic activity or acoustic signals generated by compressed air-guns on the ocean surface. The resulting data sets are subsequently used to model both the earthquake locations and the crustal structure.

Fourier domain calculation of terrain effects in marine MT

SUMMARY Magnetotelluric surveys on the seafloor have become an important part of marine geophysics in recent years. The distorting effects of topographic relief on the electromagnetic fields can be far-reaching, but local terrain is also important. Thus, computational techniques that can treat a large area containing fine-scale topography could find widespread application. We describe a new solution to the problem based on a well-established theory of electromagnetic induction in thin sheets. The procedure requires taking the Fourier transform of the integral equations derived by Dawson and Weaver in 1979, and by McKirdy, Weaver and Dawson in 1985. The equations in the transformed electric field are solved iteratively by a new technique. We prove the new iterative procedure is always convergent, whereas the original scheme diverges when the grid spacing of the discretization is small. We also give a means of correcting for distant features that need not be specified in as great detail. Preliminary tests confirm the new process is very efficient and that topographic data sets of several million points will be handled with ease.

Oceanic crustal velocities from laboratory and logging measurements of Integrated Ocean Drilling Program Hole 1256D

Drilling and logging of Integrated Ocean Drilling Program (IODP) Hole 1256D have provided a unique opportunity for systematically studying a fundamental problem in marine geophysics: What influences the seismic structure of oceanic crust, porosity or composition? Compressional wave velocities (Vp) logged in open hole or from regional refraction measurements integrate both the host rock and cracks in the crust. To determine the influence of cracks on Vp at several scales, we first need an accurate ground truth in the form of laboratory Vp on crack-free, or nearly crack-free samples. We measured Vp on 46 water-saturated samples at in situ pressures to determine the baseline velocities of the host rock. These new results match or exceed Vp logs throughout most of the hole, especially in the lower dikes and gabbros, where porosities are low. In contrast, samples measured at sea under ambient laboratory conditions, had consistently lower Vp than the Vp logs, even after correction to in situ pressures. Crack-free Vp calculated from simple models of logging and laboratory porosity data for different lithologies and facies suggest that crustal velocities in the lavas and upper dikes are controlled by porosity. In particular, the models demonstrate significant large-scale porosity in the lavas, especially in the sections identified as fractured flows and breccias. However, crustal velocities in the lower dikes and gabbros are increasingly controlled by petrology as the layer 2-3 boundary is approached.

Spatial distribution and stratigraphic characteristics of surface sediments in Taihu Lake, China

A geophysical survey was carried out for Taihu Lake, one of the largest shallow lakes in China. The StrataBox™ Marine Geophysical Instrument was applied for the first time to obtain high-resolution seismic data (in the form of vectorgraphs) of the lake sediment. Data were then interpreted by SonarWiz.Map acoustics software. Data were correlated with core stratigraphy from the lake as well as an outcrop on the northern side of the lake at Yao Bay. Results show that the upper 10 m sediment (beneath the interface of the sediment and the overlying lake water) is characterized by laminated sediments, which can be classified into two stratal types, i.e. lacustrine sediment stratum (U1) and underlying hard loess stratum (U2). The contact of these two lithologies is not continuous, and part of it is absent in the lake basin. Unequally spread over the lake basin, the lacustrine sediment (mainly consisting of sludge and muddy-clay) is found in areas along the western bank, to the northwest of the Xishan Mountains and along the northwestern side of the lake. In the rest of the lake basin, the hard loess stratum is exposed in outcrops. The depth of the lacustrine sediment ranges from 1 to 2 m, while the depth of the sludge (closely related to the modern lacustrine environment) varies from 0.03 to 1.0 m. The spatial distribution of lacustrine sediments in Taihu Lake is primarily influenced by transportation and sedimentation of riverine materials, as well as the hydrodynamics of lake currents.

構造浸食作用―太平洋型造山運動論と大陸成長モデルへの新視点―

This is a brief review of tectonic erosion originally proposed by von Huene and Scholl (1991) who have spent most of their academic careers studying marine geophysics along the circum-Pacific subduction zone. Accretionary complex is considered to be formed by trench turbidite resting on the subducting oceanic plate that accretes against a hanging wall at a shallow or deep crustal level due to off-scraping or underplating. This concept was introduced to Japan in the early 1970s and was developed in great detail to propose a new paradigm for accretionary geology that involves ocean-plate stratigraphy. Later, identification of accretionary complex on-land in Japan became the mainstream. A new idea refutes the common occurrence of an on-going accretion process forming accretionary complexes along the circum-Pacific subduction zone. Instead, the concept of tectonic erosion has emerged to explain extensive crustal thinning and subsidence as an on-going process destroying the hanging wall of an older subduction complex or even the basement of the overriding plate at more than half of the active trench. During the past three decades, marine geophysicists and geologists have documented tectonic erosion as a more common process than the formation of an accretional complex in subduction zones, and supeculate that a large volume of the continental crust is subducted into the mantle at both accretionary and erosive convergent margins. A simple calculation of the amount of subducting continental material versus arc producted at the subduction zone suggests a balance, resulting in no growth of continental crust at present (e.g. Clift and Vannuchi, 2004; Scholl and von Huene, 2007). However, considering direct subduction of intra-oceanic arcs and foundering of the continental lower crust into the mantle, we must conclude there is negative growth of the continental crust on the Earth at present.

Editorial for MGR

It is 10 years now since I accepted the then unexpected and surprise offer to co-edit Marine Geophysical Researches with Jean-Claude Sibuet and much has changed in marine sciences, as well as at the journal since that time. I remember being rather surprised and flattered at the time because I did not really consider myself a proper ‘‘geophysicist’’, but more a general marine geologist. Since that time I have managed Marine Geophysical Researches with several co-editors and came to value not only their input but also my broad-based background that I hope allowed me the oversight to make good editorial decisions and strengthen the impact of Marine Geophysical Researches. My intention has always been to make Marine Geophysical Researches accessible to a wide range of ocean and Earth scientists. I believe that Marine Geophysical Researches can and should extend its scientific impact by reaching beyond the core community of geophysicists and show what valuable insights can be derived from study of the oceans. This at least partly reflects my own background as an old-fashioned continental field geologist who only found the pleasures of marine work later in my professional life. I arrived at Marine Geophysical Researches after an unstable period at the journal and a brief publication hiatus. Since that time the journal has changed focus and recovered much of its standing in ocean sciences. Some of the changes reflect changes in marine geophysics itself. The late 1990s and 2000s saw a shift in research interest towards the geology of continental margins, compared to the mid ocean ridge systems that had dominated not only the plate tectonic revolution, but also much of the navysponsored research, especially in the United States up to that time. The start of large programmes such as MARGINS in the USA, as well as international efforts like InterMARGINS has seen renewed interest in how continental margins form and evolve. Considerable effort has gone into exploration of their resource potential, most notably in gas hydrates and this trend has been mirrored by the submissions to Marine Geophysical Researches. At the same time submissions have become more international, with far more papers submitted from Asia than was the case in 2001. It was with this trend in mind that the journal was strengthened with the addition of Dr. Shu-Kun Hsu as co-editor 2 years ago. Now I hand over my responsibilities to a new co-editor, Dr. Amy Draut from the US Geological Survey in Santa Cruz. While I shall miss Marine Geophysical Researches I know that it is in good hands because of her broad geological and geophysical expertise that complements Shu-Kun Hsu’s experience very well. I have had the privilege to know Amy Draut 13 years now, during which time we have undertaken marine and terrestrial projects together, as well as editing special collections for other journals. She is a well educated and well rounded Earth scientist, having worked on the Louisiana coast for her Ph.D., but who has broad interests in tectonics, subduction processes, marginal basins and geochemistry, as well as seismic stratigraphy. I am sure she and Shu-Kun will take Marine Geophysical Researches to new heights in the coming years. At the end of my time as co-editor I need to thank all the staff at Springer and before that Kluwer for their help in getting each issue to press. Petra van Steenbergen introduced me to the art of editing Marine Geophysical Researches and guided my first few years at the helm. More recently Robert Doe has ably stepped into this role. No AGU meeting was complete without a journal editorial P. Clift (&) Department of Geology and Petroleum Geology, King’s College, University of Aberdeen, Meston Building, Aberdeen AB24 3UE, UK e-mail: p.clift@abdn.ac.uk

John Lamar Worzel

John Lamar Worzel

Three‐dimensional magneto‐seismic reconstruction of the ‘Torre del Greco’ submerged volcanic structure (Naples Bay, Southern Tyrrhenian Sea, Italy): implications for Vesuvius’s marine geophysics and volcanology

ABSTRACTA three‐dimensional reconstruction of a large volcanic structure located offshore the town of Torre del Greco (Naples Bay, Southern Tyrrhenian Sea, Italy) and representing the seaward prolongation of the Vesuvius volcano has been carried out using integrated geological interpretation of existing densely‐spaced high‐resolution seismic and magnetic profiles. This reconstruction has provided new insights into the knowledge of marine geophysics and volcanology of Vesuvius, one of most studied volcanoes in the world.Seismic stratigraphy of the volcanic structures shows acoustically‐transparent seismic facies and high contrasts of acoustic impedance with respect to the overlying sediments. The structures have mound‐shaped external geometry and average dimensions measurable in terms of kilometres. The base of the Torre del Greco volcanic structure overlies the volcanic seismic unit correlated to the ‘Campanian Ignimbrite’ pyroclastic flow deposits. Consequently, no contrast of acoustic impedance between the two volcanic units is clearly evident on the seismic profiles. The top of the structure is irregular and eroded and shows several culminations.The three‐dimensional reconstruction of the Torre del Greco structure has been carried out using seismic constraints and correlations of volcanic structure to bathymetry. The sea floor topography is compared to the top of the Torre del Greco volcanic structure represented by contour depth of corresponding seismic horizons. Proceeding from south‐east to north‐west there is a good correspondence between the sea floor topographic surface and the top of the volcanic structure, which does not crop out at the sea‐bottom. The rising of the volcanic structure in proximity to the sea‐bottom corresponds to the occurrence of topographic undulations of up to ten metres. This evidence is confirmed by the interpretation of seismic profiles, showing three main vertical culminations of the volcanic structure, where the overlying sediment drape is significantly reduced. These culminations are linked to magnetic anomaly extremes, having values ranging between 250–350 nT. A striking coincidence between the long‐shaped topographic high on the sea floor (towards the east) and the high in the top of the volcanic structure underneath can be explained as a consequence of sea floor deformation due to the underlying volcanic culminations. Smaller volcanic mounds, buried and fossilized by marine sediments, are not related to any magnetic anomaly, probably due to their composition of volcanic tuffs.

Inversion of Scholte wave dispersion and waveform modeling for shallow structure of the Ninetyeast Ridge

The construction of S-wave velocity models of marine sediments down to hundreds of meters below the seafloor is important in a number of disciplines. One of the most significant trends in marine geophysics is to use interface waves to estimate shallow shear velocities which play an important role in determining the shallow crustal structure. In marine settings, the waves trapped near the fluid–solid interface are called Scholte waves, and this is the subject of the study. In 1998, there were experiments on the Ninetyeast Ridge (Central Indian Ocean) to study the shallow seismic structure at the drilled site. The data were acquired by both ocean bottom seismometer and ocean bottom hydrophone. A new type of seafloor implosion sources has been used in this experiment, which successfully excited fast and high frequency (>500 Hz) body waves and slow, intermediate frequency (<20 Hz) Scholte waves. The fundamental and first higher mode Scholte waves have both been excited by the implosion source. Here, the Scholte waves are investigated with a full waveform modeling and a group velocity inversion approach. Shear wave velocities for the uppermost layers of the region are inferred and results from the different methods are compared. We find that the full waveform modeling is important to understand the intrinsic attenuation of the Scholte waves between 1 and 20 Hz. The modeling shows that the S-wave velocity varies from 195 to 350 m/s in the first 16 m of the uppermost layer. Depths levels of high S-wave impedance contrasts compare well to the layer depth derived from a P-wave analysis as well as from drilling data. As expected, the P- to S-wave velocity ratio is very high in the uppermost 16 m of the seafloor and the Poisson ratio is nearly 0.5. Depth levels of high S-wave impedance contrasts are comparable to the layer depth derived from drilling data.

Editorial Submarine geomorphology: new views on an ‘unseen’ landscape

Geomorphology, one of the oldest disciplines in the geosciences, is undergoing a rebirth in the submarine environment. 2D (i.e. gridded) high-resolution bathymetry data offers exciting views of ever more of this hidden landscape, allowing a much improved understanding of both the solid Earth and Earth surface processes that shape the seabed. Such geomorphology is particularly powerful when convolved with geophysical techniques that image the sub-seafloor to form 3D studies. This journal issue promotes a vision where submarine geomorphology i) unites processes typically studied in sub-aerial geomorphology (e.g. landsliding & channel erosion) and marine geophysics (e.g. volcanism, tectonics & geodynamics) ii) strives to progress beyond purely qualitative methods and to employ quantitative approaches in analyses and iii) integrates bathymetry with other surface or subsurface data to enhance the analysis. The aim in bringing together work on the various causes and consequences of the underwater landscape is to endorse interaction and knowledge transfer between disciplines and study areas. This editorial highlights the links between submarine geomorphology, geophysics, Earth surface processes and bathymetry. Questions from the issue reviewed here include: How does the Earth melt? How does seafloor morphology affect the size of subduction earthquakes? What is the interconnection between submarinemass-wasting and tectonic environment?

Electromagnetic integral equation approach based on contraction operator and solution optimization in Krylov subspace

SUMMARY The paper presents a new code for modelling electromagnetic fields in complicated 3-D environments and provides examples of the code application. The code is based on an integral equation (IE) for the scattered electromagnetic field, presented in the form used by the Modified Iterative Dissipative Method (MIDM). This IE possesses contraction properties that allow it to be solved iteratively. As a result, for an arbitrary earth model and any source of the electromagnetic field, the sequence of approximations converges to the solution at any frequency. The system of linear equations that represents a finite-dimensional counterpart of the continuous IE is derived using a projection definition of the system matrix. According to this definition, the matrix is calculated by integrating the Green's function over the ‘source’ and ‘receiver’ cells of the numerical grid. Such a system preserves contraction properties of the continuous equation and can be solved using the same iterative technique. The condition number of the system matrix and, therefore, the convergence rate depends only on the physical properties of the model under consideration. In particular, these parameters remain independent of the numerical grid used for numerical simulation. Applied to the system of linear equations, the iterative perturbation approach generates a sequence of approximations, converging to the solution. The number of iterations is significantly reduced by finding the best possible approximant inside the Krylov subspace, which spans either all accumulated iterates or, if it is necessary to save the memory, only a limited number of the latest iterates. Optimization significantly reduces the number of iterates and weakens its dependence on the lateral contrast of the model. Unlike more traditional conjugate gradient approaches, the iterations are terminated when the approximate solution reaches the requested relative accuracy. The number of the required iterates, which for simple iterations, is approximately proportional to the square root of the lateral contrast of conductivity, in case of optimization, becomes approximately proportional to the logarithm of the lateral contrast. The effect of optimization increases with the complexity of the model under consideration. The new code is applied to a number of problems of subsurface, borehole and marine geophysics. Some of the results are compared with independent computations using different approaches.

Annalisa Griffa, A.D. Kirwan Jr, Arthur J. Mariano, Tamay M. Özgökmen and Thomas Rossby (eds): Lagrangian Analysis and Prediction of Coastal and Ocean Dynamics for Marine Geophysical Researches

Annalisa Griffa, A.D. Kirwan Jr, Arthur J. Mariano, Tamay M. Özgökmen and Thomas Rossby (eds): Lagrangian Analysis and Prediction of Coastal and Ocean Dynamics for Marine Geophysical Researches

An Archaeological Study of the Battle of the Boyne at Oldbridge, Co Meath

This paper outlines the results of a pilot archaeological study carried out on the Oldbridge Estate, Co. Meath, Ireland, in advance of its development for the presentation of the events of the Battle of the Boyne which was fought by the forces of King William III and James II on 1st July 1690. Archival research including the examination of museum collections, cartographic sources, contemporary artistic depictions of the battle and recent aerial photographic coverages was followed up by the use of a range of archaeological techniques including systematic surface collection survey, soil phosphate analysis, magnetic gradiometry, metal detecting and limited test excavation. Additionally, marine geophysics equipment was used to profile the character of the River Boyne, especially in the area of the main crossings. The study revealed important new evidence including the establishment of the location of Oldbridge village, a pivotal feature in the conduct of the battle, the confirmation of the location of the first engagement on the day of the battle and the first systematically recovered artefacts from the battlefield.

The Assimilation of Marine Geophysical Data into the Maritime Sites and Monuments Record, Northern Ireland

Northern Ireland has been subject to significant maritime influences throughout its known 9,000-year human history. In 1997, the University of Ulster, in partnership with the Environment and Heritage Service, embarked on a program of seabed mapping in an attempt to record the submerged and buried archaeological resources. To date, the geophysical research program has imaged about 80 19th- and 20th-century wrecks and about 100 targets of further “archaeological potential.” One method of integrating the results of geophysical surveys into the Maritime Sites and Monuments Record (SMR) is the use of the classification scheme CEBESSt, an alphanumeric wreck-site classification scheme based upon six site-specific variables: Composition of hull, Energy of wreck environment, Burial, Exposure, Structural integrity, and Substrate type, with t corresponding to time (the year of wrecking, if known). The classification is designed for use within a database scheme that allows for interrogation through character recognition and pattern matching.

Refresher course on marine geology and geophysics

Refresher course on marine geology and geophysics