ALBERT

Description:    This paper applies, for the first time in offshore deepwater, a method based on geographic information systems for seafloor susceptibility assessment as a first approach to marine geohazard mapping in fluid leakage areas (slope instabilities, gas escapes, seabed collapses, pockmarks, etc.). The assessment was carried out in a known seabed fluid-flow province located on the Iberian margin of the Gulf of Cádiz, Spain. The method (based on statistical bivariate analysis) creates a susceptibility map that defines the likelihood of occurrence of seafloor features related to fluid flow: crater-like depressions and submarine landslides. It is based on the statistical index ( Wi ) method (Van Westen in Statistical landslide hazard analysis. ILWIS 2.1 for Windows application guide. ITC Publication, Enschede, pp 73–84, 1997 ), in which Wi is a function of the cartographic density of seafloor features on “factor maps”. The factors selected monitor the seafloor’s capability to store and transfer hydrocarbon gases and gravitational instability triggers: geology-lithology, gas hydrate stability zone thickness (temperature, pressure–water depth and geothermal gradient), occurrence of diapirs, proximity to faults or lineaments, and slope angle of the seafloor. Results show that the occurrence of seafloor features related to fluid flow is highest where the factors “gas source and storage” and “pathways of fluid escape” converge. This means that they are particularly abundant over diapirs in contourite deposits, in the vicinity of faults, and inside theoretical gas hydrate stability fields thinned by warm undercurrents. Furthermore, the submarine landslides located on the Palaeozoic-Toarcian basement are not related to fluid leakage. This methodology provides helpful information for hazard mitigation in regional selection of potential drill sites, deep-water construction sites or pipeline routes. It is an easily applied and useful tool for taking the first step in risk assessment on a regional scale for vast areas where fluid leakage may be present, the geological model is known, and the geologically hazardous features have already been mapped. Content Type Journal Article Pages 1-17 DOI 10.1007/s11001-011-9135-z Authors Ricardo León, IGME, Geological Survey of Spain, Rios Rosas 23, 28003 Madrid, Spain Luis Somoza, IGME, Geological Survey of Spain, Rios Rosas 23, 28003 Madrid, Spain Journal Marine Geophysical Research Online ISSN 1573-0581 Print ISSN 0025-3235

Description:    Knowledge of physical properties of near-surface sediments is an important requirement for many studies of the seafloor. Dynamic or Free Fall Penetrometers (FFP), instrumented with accelerometers, are widely used to assess the mechanical properties of the sediment by deriving penetration resistance from the deceleration response of the probe as it impacts and embeds the seabed. Other field investigations, a priori knowledge or a very basic description of the type of sediment (such as a description of the sediment as soft, medium or hard) derived from studying the deceleration response (accelerometer-time histories) are used for sediment identification prior to the application of an appropriate strength determination model. In many cases this information is site-specific and in others the penetration resistance is overestimated due to the dilatory effects observed in sediment with an undetected grain fraction. In this study variables affecting a dynamic penetrometer-sediment interaction system are identified. Using data from field investigations and literature we found a relationship among five variables: peak acceleration, embedment depth, total embedment time, velocity of impact and grain size. This is used to formulate a sediment identification model. The model accounts for variables that may vary widely within one deployment and it can be applied to other FFPs with different physical characteristics (such as a different mass or size). This may lead to the increased use of FFP as a deployment tool for rapid in situ characterization of the seafloor. Content Type Journal Article Pages 1-15 DOI 10.1007/s11001-011-9116-2 Authors Gopal K. Mulukutla, Complex Systems Research Center, University of New Hampshire, Durham, NH 03824, USA Lloyd C. Huff, Center for Coastal and Ocean Mapping, University of New Hampshire, Durham, NH 03824, USA Jeffrey S. Melton, Department of Civil Engineering, University of New Hampshire, Durham, NH 03824, USA Kenneth C. Baldwin, Center for Ocean Engineering, University of New Hampshire, Durham, NH 03824, USA Larry A. Mayer, Center for Coastal and Ocean Mapping, University of New Hampshire, Durham, NH 03824, USA Journal Marine Geophysical Researches Online ISSN 1573-0581 Print ISSN 0025-3235

Description:    Data from three bathymetric surveys by R/V Kairei using a 12-kHz multibeam echosounder and differential GPS were used to create an improved topographic model of the Challenger Deep in the southwestern part of the Mariana Trench, which is known as the deepest seafloor in the world. The strike of most of the elongated structures related to plate bending accompanied by subduction of the Pacific plate is N70°E and is not parallel to the trench axis. The bending-related structures were formed by reactivation of seafloor spreading fabric. Challenger Deep consists of three en echelon depressions along the trench axis, each of which is 6–10 km long, about 2 km wide, and deeper than 10,850 m. The eastern depression is the deepest, with a depth of 10,920 ± 5 m. Content Type Journal Article Pages 1-9 DOI 10.1007/s11001-011-9134-0 Authors Masao Nakanishi, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, 263-8522 Japan Jun Hashimoto, Faculty of Fisheries, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki, 852-8521 Japan Journal Marine Geophysical Research Online ISSN 1573-0581 Print ISSN 0025-3235

Description:    Within this paper we present the Lance Insertion Retardation meter (LIRmeter) as an instrument to determine the strength of marine sediments by a measurement of the deceleration of a probe during penetration into the seafloor. The instrument has been designed for the penetration of the upper 4 m of marine sediments and is therefore suitable for site investigation applications such as cable route surveys. The LIRmeter can be easily deployed from a floating platform in water depths of up to 4,500 m. The system is suitable for long lasting missions (more than 12 h) with pogo-style measurements due to a rugged design and a special selection of sensors and electronics. The LIRmeter provides a custom data acquisition software and a web interface for acquisition setup, data download and system administration. An adaptation of the instrument to specific problems (i.e. extremely soft sediments) is possible due to interchangeable tips and adjustable weights of the lance. The specifically developed user interface and the rugged design make the instrument very easy to handle and to maintain. The sensors and the data acquisition were tested in the laboratory as well as in the field. Field measurements took place in the North Sea, where numerous measurements were performed. This paper gives an extensive description of the design of the LIRmeter (mechanics, electronics and data acquisition) supplemented by a description of data analysis and results of field- and laboratory-tests. Content Type Journal Article Category Original Research Paper Pages 1-13 DOI 10.1007/s11001-012-9156-2 Authors Sebastian Stephan, Department 5 Geosciences, Marine Technology/Sensors, University of Bremen, Klagenfurter Straße, 28359 Bremen, Germany Norbert Kaul, Department 5 Geosciences, Marine Technology/Sensors, University of Bremen, Klagenfurter Straße, 28359 Bremen, Germany Heinrich Villinger, Department 5 Geosciences, Marine Technology/Sensors, University of Bremen, Klagenfurter Straße, 28359 Bremen, Germany Journal Marine Geophysical Research Online ISSN 1573-0581 Print ISSN 0025-3235

Description:    A number of seismoacoustic T-wave events were observed between January 2003 and January 2004 by broadband ocean-bottom seismometers installed on the French Polynesia seafloor at depths of 4,000–5,000 m, well below the conjugate depth of the SOFAR channel. Using T-wave arrival times, we located 89 T-wave events along the Pacific-Antarctic Ridge. Among these, 63 events were not detected by land-based seismic observations of the United States Geological Survey (USGS), which was nearly twice the number of earthquakes reported by the USGS in the area during the observation period. We used a simple method to estimate earthquake magnitude from T-wave energy. The magnitudes of the events unidentified by the USGS ranged from 2.3 to 5.5, whereas magnitudes of the earthquakes reported by the USGS ranged from 4.1 to 6.2. Our study suggests that T-wave observations with abyssal ocean-bottom seismometers can improve the detection of small earthquakes and help our understanding of the seismotectonics of remote oceanic areas. Content Type Journal Article Category Original Research Paper Pages 1-10 DOI 10.1007/s11001-012-9158-0 Authors Aki Ito, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka-shi, Kanagawa 237-0061, Japan Hiroko Sugioka, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka-shi, Kanagawa 237-0061, Japan Daisuke Suetsugu, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka-shi, Kanagawa 237-0061, Japan Hajime Shiobara, Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan Toshihiko Kanazawa, Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan Yoshio Fukao, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka-shi, Kanagawa 237-0061, Japan Journal Marine Geophysical Research Online ISSN 1573-0581 Print ISSN 0025-3235

Description:    Fluid migration rates are important parameters for understanding the structural characteristics and evolution of the crustal tectonics and hydrocarbon exploration. However, they are difficult to measure on the seafloor. Densely sampled temperature measurements might shed light on our study of the fluid migration rates. In this study, we first use reflection seismic data to derive geothermal gradient patterns at different sub-seafloor depths, then calculated 1D vertical fluid flow models by analyzing the Péclet numbers in the offshore regions of SW Taiwan. We found Péclet numbers ranging from 2 to 5, implying that vertical fluid flow velocities are between 6 and 44 cm/year. Assumed a homogenous permeable layer and no lateral variation of the temperature fields, we analyzed possible errors caused by depth-dependent thermal conductivity and velocity-depth function. They probably cause less than 2 cm/year of errors in the estimated vertical fluid flow rate. In terms of regional fluid flow patterns, we found higher fluid flow rates near the toe of the trench, and a dramatic increase in fluid flow rate when the continental slope of the Chinese passive margin enters into the trench, and reduced fluid flow rates in the hinterland. We propose that this is a new and potentially useful method to derive regional fluid flow rate models for studying geochemical and biological processes in shallow seafloor sediments and the regional hydrological budget. Content Type Journal Article Category Original Research Paper Pages 1-10 DOI 10.1007/s11001-012-9162-4 Authors Liwen Chen, Institute of Geosciences, National Taiwan University, Taipei, Taiwan Wu-Cheng Chi, Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan Char-Shine Liu, Institute of Oceanography, National Taiwan University, Taipei, Taiwan Chun-Tien Shyu, Institute of Oceanography, National Taiwan University, Taipei, Taiwan Yunshuen Wang, Central Geological Survey, MOEA, Taipei, Taiwan Char-Yu Lu, Institute of Geosciences, National Taiwan University, Taipei, Taiwan Journal Marine Geophysical Research Online ISSN 1573-0581 Print ISSN 0025-3235

Description:    We compute the radially symmetric coherence between multibeam bathymetry and satellite gravity grids in 25 areas distributed around the world. In contrast to previous studies employing one-dimensional analysis of data along profiles, our results cannot be biased by unseen off-track topography. The mean coherence averaged over the 20–160 km waveband, and the shortest wavelength at which coherence is above 0.5, vary with tectonic setting. Seamounts and slow spreading ridges have high (〉0.7) mean coherence down to ~20 km wavelength, other spreading ridges and trenches have intermediate (0.5–0.7) coherence down to ~20–30 km wavelength, and continental shelves have low (〈0.5) coherence at all wavelengths. In the areas with highest mean coherence, the shortest wavelength at which coherence is above 0.5 decreases as mean depth decreases. The filter employed in the bathymetric prediction method of Smith and Sandwell (J Geophys Res 99(B11):21803–21824, 1994 ) selects the most coherent parts of the bathymetry and gravity spectrum. Content Type Journal Article Category Original Research Paper Pages 1-5 DOI 10.1007/s11001-012-9157-1 Authors K. M. Marks, NOAA Laboratory for Satellite Altimetry, Silver Spring, MD 20910, USA W. H. F. Smith, NOAA Laboratory for Satellite Altimetry, Silver Spring, MD 20910, USA Journal Marine Geophysical Research Online ISSN 1573-0581 Print ISSN 0025-3235

Description:    A global barotropic ocean model forced by atmospheric disturbances is developed for the detection of seafloor vertical displacements from in situ ocean bottom pressure (OBP) data. The model accuracy is validated by deep-sea OBP data at more than 100 sites obtained over the global ocean. Parameters and boundary conditions including the horizontal resolution incorporated in the ocean model are tested in order to accurately simulate the nontidal (〉2 days) OBP variations. The horizontal resolution is found to the factor that most significantly affects the simulated result. The finer the horizontal resolution applied, the smaller the model variability is. The model accuracy is highest when the horizontal resolution is 1/12°, but deteriorates when the horizontal resolution is finer than 1/12°. This may indicate a failure of the energy dissipation parameterization in the barotropic ocean model. Using the developed 1/12° model, the root-mean-square of the observed nontidal OBP component can be reduced by 18 % as an average of all the OBP data used. It is found that the 1/12° model is useful for the detection of a slow seafloor vertical displacement of centimeters related to the 2011 Tohoku-Oki earthquake from in situ OBP records near the hypocenter of the earthquake. Content Type Journal Article Category Original Research Paper Pages 1-22 DOI 10.1007/s11001-012-9151-7 Authors Daisuke Inazu, Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Sendai, Japan Ryota Hino, Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Sendai, Japan Hiromi Fujimoto, Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Sendai, Japan Journal Marine Geophysical Research Online ISSN 1573-0581 Print ISSN 0025-3235

Description:    We interpret seven two-dimensional deep-penetration and long-offset multi-channel seismic profiles in the northernmost South China Sea area, which were collected by R/V Marcus G. Langseth during the TAIwan GEodynamics Research (TAIGER) project in 2009. To constrain the crustal characteristics, magnetic inversion and forward magnetic modeling were also performed. The seismic results clearly show tilted faulting blocks in the upper crust and most of the fault plane connects downward to a quasi-horizontal detachment as its bottom in the south of the Luzon-Ryukyu transform plate boundary. North of the plate boundary, a small-scale failed rifted basin (minimum 5 km in crustal thickness) with negative magnetization probably indicates an extended continental origin. Significant lower crustal material (LCM) was imaged under a crustal fracture area which indicated a continent and ocean transition origin. The thickest LCM (up to 6.5 km) is located at magnetic isochron C15 that is probably caused by the magma supply composite of a Miocene syn-rift volcanic event and Pliocene Dongsha volcanic activity for submarine volcanoes and sills in the surrounding area. The LCM also caused Miocene crustal blocks to be uplifted reversely as 17 km crustal thickness especially in the area of magnetic isochron C15 and C16. In addition, the wide fault blocks and LCM co-existed on the magnetic striped area (i.e. C15–C17) in the south of the Luzon-Ryukyu transform plate boundary. Magnetic forward modeling suggests that the whole thick crustal thickness (〉12 km thick) needs to be magnetized in striped way as oceanic crust. However, the result also shows that the misfit between observed and synthetic magnetic anomaly is about 40 nT, north of isochron C16. The interval velocity derived from pre-stack time migration suggests that the crust is composed of basaltic intrusive upper crust and lower crustal material. The crustal nature should refer to a transition between continent and ocean. Thus, the magnetic reversals may be produced in two possible ways: basaltic magma injected along the crustal weak zone across magnetic reversal epoch and because some undiscovered ancient piece of oceanic crust existed. The crustal structure discrimination still needs to be confirmed by future studies. Content Type Journal Article Category Original Research Paper Pages 1-20 DOI 10.1007/s11001-012-9154-4 Authors Yi-Ching Yeh, Institute of Applied Geosciences, National Taiwan Ocean University, 2 Beining Road, Keelung, 20224 Taiwan Shu-Kun Hsu, Institute of Geophysics, National Central University, 300 Chungda Road, Jhongli, 32001 Taiwan Wen-Bin Doo, Institute of Geophysics, National Central University, 300 Chungda Road, Jhongli, 32001 Taiwan Jean-Claude Sibuet, Institute of Geophysics, National Central University, 300 Chungda Road, Jhongli, 32001 Taiwan Char-Shine Liu, Institute of Oceanography, National Taiwan University, 1, Sec.4 Roosevelt Road, Taipei, 10617 Taiwan Chao-Shing Lee, Institute of Applied Geosciences, National Taiwan Ocean University, 2 Beining Road, Keelung, 20224 Taiwan Journal Marine Geophysical Research Online ISSN 1573-0581 Print ISSN 0025-3235

Description:    During summer of 2009, multi-channel marine seismic reflection data and wide-angle refraction data were acquired as part of the joint NSF and Taiwanese-funded TAIGER program with the goal of understanding the dynamics of arc-continent collision in Taiwan. One of the principle difficulties of crustal-scale imaging with marine reflection data such as these is the prevalent multiple contamination that obscures many of the deep crustal targets. Without effective treatment of multiples, many of the objectives of the TAIGER active source program may not be achieved. We present three profiles, one from each acquisition leg, that demonstrate the effectiveness of 2D surface-related multiple elimination (SRME) and radon filtering in attenuating much of this unwanted energy in broad ranges of water depths, seafloor topographies and lithologies. Two profiles from south of Taiwan image 3–4 km of sedimentary strata overlying moderately extended continental crust along the Eurasia continental shelf and a 5–6 km thick sedimentary section overlying thin crust consisting of faulted blocks and volcanic bodies along the continental slope. Our multiple attenuation efforts also reveal a seaward-dipping normal fault that penetrates into the upper mantle and separates thick crust of the continental shelf from thin crust of the continental slope. A profile from east of Taiwan reveals thin ocean crust of the Philippine Sea plate subducting beneath the Ryukyu trench that may be traced beneath the accretionary prism and Ryukyu forearc. These profiles demonstrate the success of our imaging strategy in the range of imaging environments spanned by the TAIGER marine reflection seismic data. Content Type Journal Article Category Original Research Paper Pages 1-17 DOI 10.1007/s11001-012-9149-1 Authors Ryan Lester, Institute for Geophysics, University of Texas, Austin, TX, USA Kirk McIntosh, Institute for Geophysics, University of Texas, Austin, TX, USA Journal Marine Geophysical Research Online ISSN 1573-0581 Print ISSN 0025-3235