Collection Of Geophysical Data Research Articles

Trends in the Acquisition and Accessibility of Long-Term Solar-Terrestrial Data

Solar-Terrestrial Physics (STP) programs involving global data acquisition have characterized international science in the 20th Century and made necessary the creation of a system of national and international data centers. Under aegis of the International Council of Scientific Unions, the World Data Center (WDC) system was established in 1957 to provide a voluntary mechanism for the collection, copying, exchange, and dissemination of geophysical and solar data taken by International Geophysical Year projects. At first, WDCs collected mainly analog data recorded by monitoring arrays of IGY instruments. In the three decades since IGY, techniques shifted from mainly analog recording to digital, and data centers shifted from mainly servicing analog images on film and publishing summary tables to providing numerical data on digital media for computer analysis.In the 1960s, WDCs began to provide collection and dissemination of information and derived data products as well as original data. During the late 1970s, merged multi-component data sets were created on central host computers to support joint analysis projects by groups of scientists and individuals. A major trend in the late 1980's is acquisition and merger of large digital data sets from ground-based and satellite sensors. The data are made available on high density computer media (particularly CD-ROM optical discs) together with summary analog images and access software for browsing or moving data from the storage media to other computers. Tables and images are still published in the 1990s and are especially needed in places with limited access to personal computers and lacking easy connections to on-line central data collections.The cumulative amount of STP data held by WDC-A has grown substantially since 1957. However, each year since the early 1960s has shown a decline in the global coverage of key types of data as monitoring networks diminished. The rise in cost to process large digital databases produced by modern instruments and the high cost of labor-intensive analog data reduction has contributed to the annual decline of some types of data deposited with the WDCs. Finally, there is a situation that is difficult to quantify; namely, some key geophysical observing sites are located in countries that seldom use their output. During periods of economic stress these facilities receive low priority for continued operation. Under current world conditions, it is difficult for some nations to justify the continued expense to continue operating basic monitoring sites, e.g., magnetic observatories, ionosondes, and other instruments that produce essential records needed as input for general models, planetary indices, or other often-used, basic global data products.

The unmanned geophysical data collection platform based on the digital magnetometer CMVS-6

The polar geomagnetic research laboratory of Izmiran carries out construction on the automated digital data collection platform for operation in the remote regions including Antarctica. In view of the experience with previous instruments such as CMVS-2, a new digital magnetometer CMVS-6 was designed. CMVS-6 consists of a few separate modules: quartz sensors unit, electronic unit with cassette tape recorder, control and adjustment unit and radioisotopic thermoelectric generator (RITEG). Data sample rate is 1, 10 or 60 s (selectable) and the system includes the measurement of D, H and Z components of the magnetic field and has three channels for additional sensors with electric output. Resolution is 0.5 nT for magnetic field and 1.25 mV for electric channels. The dynamic range is 4000 nT for a magnetometer and 10 V for electric channels, but CMVS-6 can operate properly in dynamic range 1.8 times greater. The data are stored on the cassette tape recorder. Control and adjustment are necessary only for initial installation of the platform and for the data flow checking. It is planned to use the riometer, d.c. electric meter and thermometer as additional sensors. The first platform is installed in the Antarctic for testing in 1987–1988 season.

A satellite-based digital data system for low-frequency geophysical data

Abstract A reliable method for collection, display, and analysis of low-frequency geophysical data from isolated sites, which can be throughout North and South America and the Pacific Rim, has been developed for use with the Geostationary Operational Environmental Satellite (GOES) system. Geophysical data primarily intended for earthquake hazard and crustal deformation monitoring are digitized with either 12-bit or 16-bit resolution and transmitted every 10 min through a satellite link to a bank of UNIX-based computers in Menlo Park, California. There the data are available for analysis and display within a few seconds of their transmit time. This system provides real-time monitoring of crustal deformation parameters such as tilt, strain, fault displacement, local magnetic field, crustal geochemistry, and water levels, as well as meteorological and other parameters, along faults in California and Alaska, and in volcanic regions in the western United States, Rabaul, and other locations in the New Britain region of the South Pacific. Various mathematical, statistical, and graphical algorithms process the incoming data to detect changes in crustal deformation and fault slip that may indicate the first stages of catastrophic fault failure. Alert trigger levels based on physical models, signal resolution, and previous history have been defined for particular instrument types. Computer-driven remote paging and mail systems are used to notify appropriate personnel when alarm status is reached. The system supports continuous historical records of low-frequency geophysical data, software for extensive analysis of these data, and programs for modeling fault rupture with and without seismic radiation, as well as providing an environment for real-time attempts at earthquake prediction.

An introduction to the European Geotraverse Project: First results and present plans

The European Geotraverse (EGT) is an international, multidisciplinary project focused on a north-south orientated lithospheric profile, 4000 km long and of varying width, extending from northernmost Scandinavia to North Africa. This profile consists of three interlinking Segments (Northern, Central, and Southern) comprising a continuous succession of tectonic provinces ranging from the oldest Precambrian areas of the Baltic Shield to the currently active area of the Western Mediterranean. The broad aim of the EGT Project is to obtain a better three-dimensional picture of the structure, state, and composition of the continental lithosphere to use as a basis for an understanding of its evolution and dynamics. All of the 12 major projects that constitute the EGT “Joint Programme” have now been initiated, and several of these projects are nearing completion. Along the Northern Segment, data from “The Fennoscandian Long-Range Project” (FENNOLORA), a 2000 km long seismic profile across the Precambrian Baltic Shield, show that except beneath southern Sweden, the Shield is characterized by a high-velocity, 40–50 km thick crust—including a 5–10 km thick crust-mantle transition zone. An alternating series of 4–6 high- and low-velocity zones is present in the subcrustal lithosphere, the base of which increases in depth from ca. 110 km to ca. 230 km from south to north beneath the Shield. The top of the mantle transition zone lies at a depth of about 450 km. The second major project along this Segment, the EUGENO-S (European Geotraverse Northern Segment—Southern Part) project, is a multidisciplinary study of the Fennoscandian Border Zone, and was largely completed in 1984 with the realization of a large-scale seismic experiment. Preliminary interpretation of the excellent data obtained indicate the presence of strong lateral variations in internal crustal structure beneath the Danish Basin. Field work for a third major project, a multidisciplinary transect of the Archaean and Early Proterozoic terrains in the northernmost part of the Shield (the “Polar Profile”), was carried out in 1985. A series of deep seismic reflection lines has so far been realized in the area of the Central Segment in the context of German national programmes. First interpretations of the seismic data from a 260 km long profile across the two main intra-Variscan (Hercynian) lineaments have shown the presence of numerous horizons making up a highly reflective zone in the lowermost 10 km of the crustal section studied, and distinct changes in reflectivity between the main Variscan tectonic zones. In 1986, the entire Segment will be investigated in detail in an ambitious international programme of integrated geological and geophysical studies. A series of seismic experiments (termed EGT-S) have been carried out across the Southern Segment (in 1982, 1983, and 1985). Interpretation of data from the 1982 and 1983 experiments have led to several interesting results, including: 1. (1) the suggestion that two “crust-mantle”-like interfaces exist beneath the Po Basin (at depths of about 35 and 50 km) and adjacent tectonic units, these interfaces marking a deep contact zone between the Adriatic and European plates, 2. (2) in the area between Genoa and Corsica, the Ligurian Sea is underlain by a greatly thinned, distinctly layered section of continental crust, and 3. (3) Corsica and Sardinia are underlain by bowl-shaped, “typically” Variscan continental crusts. The 1985 phase of seismic surveys focused on crustal structure beneath Tunisia and the adjacent seas. In addition, two off-traverse projects are being realized. First, a wide-aperture network of autonomously recording seismic stations (“NARS”), installed along the line Gothenburg-Málaga between 1982 and 1984, is already yielding high-quality data on the upper 600–700 km of the mantle. Second, an investigation of lithospheric seismic anisotropy in the area of the Iberian Peninsula is being organized for 1987–1988. Finally, of great importance are the systematic compilation of existing data and, where needed in critical regions, collection of new geophysical and geological data presently being carried out for the entire area encompassed by the EGT. It is expected that these compilations will be completed by 1987, at about the same time that full results from the main large-scale seismic experiments become available, enabling the construction of an integrated lithospheric cross-section along the EGT, requiring a final phase of intensive multidisciplinary collaboration.

Arbitrariness, uniqueness and optimization

The collection, processing and modelling of geophysical data are three important phases in obtaining and interpreting geophysical information. They form part of a feed-back loop in which lessons learned during the later phases are used to modify procedures used in the earlier phases.

Geomagnetic Research in the Americas

THE earth is a great laboratory in which Nature is constantly performing physical experiments. The student of earth physics labours under the disadvantage that systematic and trustworthy data are available for little more than a century. This period is too limited from which to draw many significant conclusions regarding the complex world-wide and cosmical causes and interrelationsinvolved. In the collection of geophysical data, chief attention must be given to geographical and space-distribution and to variability with time characterizing the phenomena concerned. These data must include not only isolated observations on land and sea but also continuous observations at fixed observatories to follow simultaneous variations with time and co-ordination with experiment in the physical laboratories and astrophysical observatories.