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- Volume 22, Issue 9, 2004
First Break - Volume 22, Issue 9, 2004
Volume 22, Issue 9, 2004
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Corruption and loss: ptifalls in seismic data management
By E.L. JackCan you really trust your data? Eleanor Jack, senior geophysicist, Landmark Graphics, offers some cautionary tales about what can go wrong with stored seismic data and what companies can do to better manage and protect their data. It is usually assumed, at least by the data owner, that when copying data from one medium to another, all the data on the original are safely transferred to their destination. Data management papers generally tend to reinforce this view, with flow charts using boxes and arrows to indicate data transfer, which by implication is seamless and trouble-free. But sadly this is not always the case, as this paper will demonstrate. Data can get lost or corrupted and this corruption waits unnoticed, like a sleeper, until the data are needed. Data transcription and copying are generally outsourced activities performed by a specialist company. Such a company will be expert at transferring data in the most efficient manner, with well-tried transcription software to translate the various acquisition and processing formats into the standard exchange format, SEG-Y. All reputable transcription companies will also perform some level of quality control. However, a combination of cost pressures and lack of understanding of the nature of the data and their formats mean that a significant percentage of data is archived with hidden corruption or loss. Some typical examples, which escaped this initial QC check, are shown here.
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News Feature: US agency finds seismic operations have no significant impact on marine mammals
It’s the outcome that the oil industry had been hoping for. A major environmental impact assessment by the US Department of Interior’s Minerals Management Service (MMS) has concluded that seismic survey operations in the Gulf of Mexico do no discernible harm to marine mammal life. We summarise here some of the key points from the findings, the implications of which may reverberate beyond US offshore activities. In announcing the completion of an environmental assessment (EA) evaluating the potential environmental impacts of geological and geophysical (G&G) activities in the Gulf of Mexico, the Minerals Management Service (MMS) said that the best available information on the effects of seismic surveys on marine resources was analyzed, and in particular marine mammals, including sperm whales. Hundreds of documents were reviewed from around the world. The activities taken into account in the EA include seismic surveys, deeptow side-scan surveys, electromagnetic surveys, geological and geochemical sampling, and remote-sensing surveys which are used extensively to support oil and gas exploration in the Gulf of Mexico. The impact-producing factors considered in the EA included seismic survey noise, vessel and aircraft noise, seafloor disturbance, and space-use conflicts with seismic arrays. Each year there are about 20 MMS-permitted 3D seismic surveys conducted in the Gulf of Mexico. The conclusion of the EA was that G&G activities are not expected to result in significant adverse impacts to any of the potentially affected resources. Potentially adverse but not significant impacts were identified for marine mammals, except the manatee, for which negligible impacts were identified. As a result, MMS has issued a ‘Finding of No Significant Impact.’ The EA will be included as part of an information package used by MMS in the near future to petition the National Oceanic and Atmospheric Administration (NOAA). This petition will request NOAA to issue regulations to allow small ‘takes’ incidental to seismic surveys in the Gulf of Mexico, under the enabling regulations of the Marine Mammal Protection Act. The MMS currently requires operators engaged in activities on the US Outer Conbtinental Shelf (OCS), including G&G activities, to comply with a number of lease stipulations, Notices to Lessees, and other mitigation measures designed to reduce or eliminate impacts to sensitive environmentalresources from impact-producing factors such as vessel or aircraft traffic, anchoring, and trash and debris. These mitigation measures are required under the OCS Lands Act, the Endangered Species Act, and the Marine Mammal Protection Act to ensure environmental protection, consistent environmental policy, and safety. As part of the impact analyses completed in the G&G EA, current protective and mitigation measures were evaluated (Alternative 1). Additional feasible mitigation measures were also considered (Alternatives 2 and 3), as were potential restrictions on concurrent operations within close proximity to one another (Alternative 4), as viable alternatives to further reduce the potential for impacts to marine mammals. The PEA reviewed G&G activities which were the subject of a previous Environmental Impact Statement (EIS) prepared by the US Geological Survey in 1976 and a PEA prepared by the MMS in 1984. A new PEA was needed in light of advances in G&G technology, expansion of activities into deep offshore waters, and improved knowledge of acoustic impacts on marine life. Further, those G&G activities that were previously determined to be categorical exclusions (CATEXs), exempt from detailed analysis (based on previous environmental documents), needed to be revisited and re-evaluated.
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US project focuses on what makes the Earth move
By J.R. StowellJohn R. Stowell, president, Mount Sopris Instrument Company, Colorado reports on the near surface geophysics elements of the EarthScope project in the US, set up to study the structure, evolution and dynamics of the North American continent. The historical record is filled with striking reminders that the ‘terra firma’ upon which we live is far from firm. From the ancient eruptions at Pompeii to more contemporary events at Krakatoa, San Francisco, Mount St. Helens, and Kobe, an observer can easily assume that our earth’s near surface is a dynamic system. In the late 18th Century, Hutton and others startled the scientific (and theological) communities by proposing a completely new model of planet Earth. Based on observations and evidence on several continents, ideas about the age and composition of the subsurface took a dramatic turn. Over the next century, support of these radical propositions grew and became generally accepted by the scientific community. And in the last 30 years, Hess and others have applied global and extra-terrestrial observations in support of the general theory of plate tectonics. Not only was the earth an extremely old orb of layered material, but its crust was in constant, if extremely slow deformation. Oceans’ ridges were extruding new material while continent-sized plates were grinding old rock back down into the earth’s interior. Catastrophes like Mount St. Helens and Kobe have shown that sudden changes in the ‘near surface’ can cause serious economic and environmental consequences. So it is not surprising that national and international political bodies have asked the global scientific community for help in minimizing the effects of such activity. In Japan and the US, several programmes have been funded to meet this challenge. In the US, the National Science Foundation (NSF) is responsible for a programme called EarthScope. NSF is an independent agency of the US government established by the National Science Foundation Act of 1950. The mission of EarthScope is to apply modern observational, analytical and telecommunications technologies to investigate the structure and evolution of the North American continent and the physical processes controlling earthquakes and volcanic eruptions. EarthScope includes a multi-purpose array of instruments and observatories that will greatly expand the observational capabilities of the earth sciences and permit better understanding of the structure, evolution and dynamics of the North American continent. Two components of EarthScope deal with near-surface geophysics. One, called the San Andreas Fault Observatory at Depth (SAFOD) is well under way. SAFOD (Fig. 1) is designed to directly sample fault zone materials (rock and fluids), measure a wide variety of fault zone properties, and monitor a creeping and seismically active fault zone at depth. A 3.2 km deep hole will be drilled through the San Andreas fault zone close to the hypocentre of the 1966 M~6 Parkfield earthquake, where the San Andreas fault slips through a combination of small-to-moderate magnitude earthquakes and a seismic creep. As of early August, drilling had reached ~1450 m where 13 3/8 in casing had been set in preparation for the next drilling phase. At a depth of approximately 3 km, the hole will be kicked off in an attempt to drill through the fault system.
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Environmental geophysics investigations in urban areas
More LessDr John M. Reynolds, managing director and principal geophysicist at Reynolds Geo- Sciences, presents some case histories illustrating how the obstacles of noisy urban sites have been overcome to produce highly useful interpretable data sets, often far exceeding the expectations of the clients involved. Urban areas represent some of the most challenging environments in which to undertake geophysical investigations. Restricted space, the necessity for traffic management, high ambient noise (electrical and vibration), underground utilities, etc. all help to complicate the design and setting out of the geophysical profiles or grids. In many cases, such sites could not be investigated as the acquisition methods, the type of equipment and subsequent data processing software were not readily available. Over the last few years, significant changes in the capabilities of the equipment and software have permitted geophysical surveys to be undertaken in these hitherto inappropriate areas. The first case history at Field Road, Reading, Berkshire, was by far the largest, most complex and technically challenging. It shows how with very careful survey design, particular attention to data acquisition, and specialist data reduction and modelling, a labyrinth of shallow chalk mine galleries were mapped successfully using micro-gravity. The second involved a housing development in northwest London where the intrusive investigations had failed to satisfy the requirements of the Environment Agency, the environmental regulator in England and Wales (Scotland has a separate but similar regulatory body). Furthermore, the client and his engineering advisers were sceptical about the use of geophysics. Despite the technical difficulties of a complex partially developed site, the geophysical investigation demonstrated clearly the benefits of such a survey when integrated with intrusive investigations targeted on the basis of the geophysical survey. The client and his advisers became keen advocates of the use of geophysics once the results were made known. The third example is a complete contrast to the first two in that, despite the site being in a town, it comprised open space. The method used was the tried and tested and now very well established technique using a Geonics EM31 ground conductivity meter. (Detailed descriptions of geophysical methods discussed here have been presented by Reynolds (1997)). It demonstrates that even simple, long established techniques used very simply can produce some very clear and graphic results. The last case history involved the development of a former landfill site in south Wales. The 12.6 ha site was being cleared and earthworks to level the site were well in progress. At this late stage, it was suggested that steel drums might have been buried on the site but their location was unknown. A detailed geophysical investigation on the extremely busy construction site was undertaken using predominantly magnetic gradiometry and drum graves were located successfully and proven by excavation. The additional feature of all these case histories has been the involvement of what has subsequently become known as an ‘Engineering Geophysics Adviser’, an extremely experienced geophysicist (or group of geophysicists) independent of the geophysical contractor. This role has been advocated within the most recent guidelines for the use of engineering (and environmental) geophysics (McDowell et al., 2002).
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Developing geophysical techniques for detecting unexploded ordnance
Authors J.M. Stanley and M.K. CattachJohn M Stanley, chief technology officer, and Malcolm K Cattach, director, research and development division, of Australian company Geophysical Technology (G-tek) reflect on the increasing demand for cost effective detection of unexploded ordnance. The problem of buried hazard remaining from unexploded ordnance (UXO) has been with us since the first use of explosives in ordnance. During the major twentieth century conflicts, it was not uncommon for the failure rate in explosive ordnance to be as high as 20%, resulting in a very large number of these weapons remaining in the ground long after the conflict ceased. These weapons are still causing injury, death and damage when disturbed or when their contents leak into the groundwater system. UXO also provide a potential source of explosives for terrorist interests. In addition to UXO remaining from conflict, a major source of environmental contamination has been military training activity. To put some perspective on the extent of this problem, the office of the Secretary of US Defense reported: ‘The UXO clean-up problem is a very large-scale undertaking involving 10 million acres of land at some 1400 sites. Estimated cleanup cost of current UXOs is tens of billions of dollars’. The problem is not confined to the US. It is generally believed that matters are worse in Eastern Europe than in the US. It is unlikely that there is a country in the world where contamination and explosive hazard from UXO does not exist. Detecting the presence of UXO in the ground presents a task for which geophysicists familiar with the characteristics of the near-surface environment are well equipped. Moreover, the geophysical community involved in the UXO industry is now setting standards of quality procedure from which our colleagues in oil, gas and minerals exploration may well learn. Since when has an exploration geophysicist been held responsible for not finding a resource that current technology was capable of detecting?
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High resolution geophysics provides optimal results on inland waterways
By T. TóthTamás Tóth of Hungarian survey company Geomega provides some convincing evidence for why a combination of geophysical technologies will provide the best result when surveying shallow water sites for environmental and engineering purposes. Detailed modelling of the shallow subsurface is often a must for engineering and environmental studies. High-resolution geophysics combined with shallow boreholes can provide a cost effective solution for these investigations. In many cases a significant step forward can be achieved simply by extending the 1D information provided by the boreholes into 2D, or still better, into 3D using geophysical techniques. Obviously this is a critical step at locations where the subsurface shows high variability in vertical and/or horizontal directions. We are all aware that high variability is often characteristic of the near surface region, and mapping the shallow subsurface in 3D using geophysical techniques can be a challenging task. This is especially true for those areas which are covered by water. Natural or artificial waterways, lakes, rivers and canals often present an obstacle for mapping simply due to the difficulties accessing the area. A lucky contra version is that, in many cases, performing a geophysical survey on water is simpler, quicker and therefore cheaper than a similar survey on land. Sometimes the resolution of the survey performed on water is actually superior to a land survey. This is typically the case for seismic surveys for example. Surveying water covered areas presents difficulties, but some of these can be overcome by applying new technologies. A good example is positioning, which used to be a challenging task on water a few decades ago, but became relatively simple nowadays using high precision GPS (DGPS and RTK GPS) technologies. Accuracy of these positioning techniques became adequate for high-resolution geophysical surveys, in the process making even detailed 3D surveys on waterways feasible. Every geophysical technique has its limitations and there is no ‘magic tool’ in the hands of geophysicists. Seismic, electric, electromagnetic or magnetic techniques can be applied separately or combined depending on the actual problem. We are, however, convinced that in many cases application and joint evaluation of more than one geophysical technique can provide an added value. An example for this is the combined application of seismics and GPR which enables a direct calculation of physical parameters like density, acoustic and electromagnetic velocities using the geophysical data only. In this paper examples of water borne geophysical surveys will be presented with special emphasis on the importance of 3D imaging. An example of combined seismic and GPR surveys with an environmental focus will be discussed as well.
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Applications of ground penetrating radar in archaeological and forensic contexts
By A.P. AnnanA.P. Annan, Sensors & Software, provides examples of how GPR can uncover both the ancient and unexpected from shallow ground. Ground penetrating radar (GPR) now sees widespread use for many shallow mapping applications. The basic principles are summarized by Davis & Annan (1989). The most intriguing uses always seem to involve archaeology and forensics. The search for anthropogenic subsurface features – whether historical or criminal in context – always create discussion and comment. The news media regularly announces GPR being used to locate bodies such as that of the late Jimmy Hoffa or to unearth the lost city of Atlantis. While exciting, the real successes seldom reach the public media. Those in the UK who watch the Time Team on television will have some sense of the excitement and treasure hunt aspect of using geophysics for archaeology. In this article we will present three interesting applications of GPR for archaeological/forensic type applications. There are many such instances which can be cited. The following were chosen for their specific relevance to a geophysical audience.
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Recent advances in 3D land processing: Examples from the Pakistan Badin area
Authors A. Karagül, R. Crawford and S. AliThe Badin Concession is relatively mature with many small oil fields which collectively account for about 50% of Pakistan’s current oil production. In total about 220 wells have been drilled in the area. Between 2000-2002, BP acquired over 2500 Km2 of 3D data over the Badin area using a non-orthogonal geometry. We demonstrate the improvement in data quality gained from the application of two recent advances in 3D processing - 3D velocity filtering to attenuate the linear noise, pre-stack (Meunier, 1999) and 3D acquisition footprint attenuation, post-stack (Soubaras, 2002). The Badin-1 Petroleum Concession was granted in 1977 and the first discovery (Khaskeli field) was made in June 1981. Since then 54 fields have been discovered. The first 2D seismic was shot in 1977-78 and overall about 17,000 line km have been recorded. A number of smaller 3D seismic volumes have been recorded since 1996 covering individual fields. Most recently, between 2000-2002, approximately 2500 Km2 of 3D data have been acquired (Figure 1). This includes the 100 Km2 acquired over the Mehran Concession.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)