Imaging the seabed in shallow water areas (<300m) using 3D seismic surveys

This report discusses imaging the seabed from exploration 3D seismic data in shallow water areas, defined as less than 300m. The issues involved are discussed primarily with reference to data sets within the Faroe-Shetland Channel (FSC) where the bulk of the seabed imaging work has been performed and where the availability of other data such as swath bathymetry permit detailed comparison. The report then considers how seafloor conditions and survey design influence seabed reflection quality. A method for mapping seabed topography using seabed multiple energy is presented and applied to the FINA 30/14 3D survey in the Central Graben of the North Sea. The major conclusions of this report are: (1) In water depths shallower than 300-400m and in areas of high seabed velocity, the seabed reflection on conventionally processed 3D seismic volumes tends to become poorly imaged if the survey has been designed for deep targets. (2) Pre-stack processing of the seismic volume to enhance seabed multiples does appear to generate a plausible surface on the Fina survey. The first multiple is less contaminated with survey footprint artefacts than the primary reflection. The auto-correlation pick provides the most coherent surface in this study. An unresolved question is the extent to which the derived topography reflects tuning effects due to the rapidly varying thickness of the Forth Formation, as opposed to the true seabed topography. (3) The technique may usefully be applied to another, deeper water area, such as Shell’s woc96 survey in the FSC where the primary seabed reflection begins to fade. This would enable a direct comparison of surfaces generated by conventional and multiple enhancement processing as well as present an opportunity to extend the FSC seabed image

Lophotrichus as a Cellulolytic Genus

The genus Lophotrichus was based by Benjamin (Mycologia 41 :346-354. 1949) on two species, one from Illinois, L. ampullus, selected as the type species, and one from Peru, L. martinii. Both were isolated from dung. The general habit of these fungi, the character of the perithecia, and the lemon-shaped spores produced in evanescent asci clearly suggest their close relationship with Chaetomium. Benjamin placed them in a distinct genus of the Chaetorniaceae, because of their long necks and their submerged habit of growth, both on dung and on agar media. The original isolation of L. martinii was from dung collected at Talara, Peru, in September, 1945. At the same time and place some dead grass was collected and kept in a sterile packet. This second collection, when wet over three years later, also produced L. martinii. In this case, however, the perithecia were superficial on the substratum exactly as are those of Chaetomium. (Fig. E) Another isolation of L. ampullus from litter collected near Douglas Lake, Michigan, showed exactly the same superficial habit of growth. This fact and the isolation of both species from plant debris suggest that the species of Lophotrichus are not primarily coprophilous but are basically cellulolytic, and that their appearance on dung is, like that of Chaetomium, more or less incidental. It was for this reason that the following tests were run to determine the cellulolytic powers of Lophotrichus and also its habit of growth

Bank lending networks, experience, reputation, and borrowing costs.

We investigate the network structure of syndicated lending markets and evaluate the impact of lenders’ network centrality, considered as measures of their experience and reputation, on borrowing costs. We show that the market for syndicated loans is a “small world” characterized by large local density and short social distances between lenders. Such a network structure allows for better information and resources flows between banks thus enhancing their social capital. We then show that lenders’ experience and reputation play a significant role in reducing loan spreads and thus increasing borrower’s wealth.agency costs, bank syndicate, experience, loan syndication, reputation, small world, social network analysis.

Snow cover of Central East Antarctica (Vostok station) as an ideal natural spot for collecting Cosmic Dust: preliminary results on recovery of chondritic micrometeorites.

第3回極域科学シンポジウム/第35回南極隕石シンポジウム 11月29日（木）、30日（金） 国立国語研究所 2階講

The Afen Slide

Summary Identified in 1996, as part of an environmental survey for the Atlantic Frontiers Environment Network (Graham et al 1996, Masson et al 1996), the Afen Slide lies around 95 km northwest off the Shetland Islands. Using seabed picks from 3D exploration seismics reveals the detailed morphology of the slide (Bulat 2001) enabling interpretations about the phases and nature of movement to be made. The head of the slide is at water depth of 830 mbsl and the debris lobe stretches to over 1120 mbsl along a slope varying from >2o to <1o. The overall length is in excess of 12 km and the maximum width attained is around 4.5 km. The relative timing of the various phases can be determined with some certainty although the absolute age of the slide or the various phases is more difficult to confirm. There are two 14C dates from the area, one from the surficial sediments within the slide scar (Holmes et al 1997) and the other from within the debris lobe. These suggest a possible first movement at around 16,000 –13,000 years BP with the later retrogressive phases occurring after 5,800 years BP. These are highly speculative, as the exact relationship of the dated material to the post slide stratigraphy is not known. The seismic data combined with information from previous studies indicates that sedimentation in the area is controlled by along slope processes; mounded elongate contourites can be traced through the surrounding area. The seismic record suggests that the depositional environment has remained remarkably consistent since the onset of the last glacial. This may have contributed to the conditions that combined to produce slope failure in this particular area. An abundance of contouritic sands predisposed to liquefaction interspersed with fine-grained low permeability muds would provide a plane of weakness along which failure could propagate. However, the seismicity, necessary to cause liquefaction, during the period in question is not known although threshold values for failure have been calculated to be within the 10,000 yr return period (Hobbs et al 1997)

Bank lending networks, experience, reputation, and borrowing costs

We investigate the network structure of syndicated lending markets and evaluate the impact of lenders’ network centrality, considered as measures of their experience and reputation, on borrowing costs. We show that the market for syndicated loans is a “small world” characterized by large local density and short social distances between lenders. Such a network structure allows for better information and resources flows between banks thus enhancing their social capital. We then show that lenders’ experience and reputation play a significant role in reducing loan spreads and thus increasing borrower’s wealth.Agency costs, bank syndicate, experience, loan syndication, reputation, small world, social network analysis.