Shelton S. Alexander

Magsat equivalent source anomalies over the southeastern United States - Implications for crustal magnetization

The Magsat crustal anomaly field depicts a previously-unidentified long-wavelength negative anomaly centered over southeastern Georgia. Examination of Magsat ascending and descending passes clearly identifies the anomalous region, despite the high-frequency noise present in the data. Using ancillary seismic, electrical conductivity, Bouguer gravity, and aeromagnetic data, a preliminary model of crustal magnetization for the southern Appalachian region is presented. A lower crust characterized by a pervasive negative magnetization contrast extends from the New York-Alabama lineament southeast to the Fall Line. In southern Georgia and eastern Alabama (coincident with the Brunswick Terrane), the model calls for lower crustal magnetization contrast of − 2.4 A/m; northern Georgia and the Carolinas are modeled with contrasts of − 1.5 A/m. Large-scale blocks in the upper crust which correspond to the Blue Ridge, Charlotte belt, and Carolina Slate belt, are modeled with magnetization contrasts of − 1.2 A/m. 1.2 A/m. and 1.2 A/m respectively. The model accurately reproduces the amplitude of the observed low in the equivalent source Magsat anomaly field calculated at 325 km altitude and is spatially consistent with the 400 km lowpass-filtered aeromagnetic map of the region.

Issues in the Transborder Flow of Scientific Data

The US National Committee for CODATA is conducting an interdisciplinary study of international access to scientific data. The primary focus is on data in electronic forms, a topic of increasing complexity and importance in scientific research and international collaboration. The study is characterizing the technical, legal, economic and policy issues that have an impact — whether favorable or negative — on access to data by the scientific community. Special attention is being given to the specific conditions inherent in the transborder transfers of electronic scientific data among the academic, governmental and private sectors. The study is also identifying and describing those barriers that have the most adverse impact in each of the discipline areas within CODATA’s purview — the physical, astronomical, biological and geological sciences — and across those disciplines, using representative examples. Finally, it is attempting to identify trends that are likely to have significant discipline-specific and interdisciplinary impacts on the use of scientific data, particularly in electronic forms, and will suggest approaches that could help overcome both generic and specific barriers to access in the international context. Because of the broad nature of this topic it is important to maintain an appropriate focus on key issues and this will be done in part through the use of representative case studies. The study will be completed by the fall of 1996.

A neural network approach to seismic event identification using reference seismic images

A data compression neural network is known to have both data compression capability and generalization capability. In this study, a data compression neural network is trained using reference seismic images to rapidly identify natural earthquakes and underground explosions. The method developed is based on the generalization properties of the trained neural network and a quantitative measure of the degradation of the reconstructed image over the population of similar events and dissimilar events (i.e. explosions vs earthquakes). As examples, this approach is applied to a dataset of 11 natural earthquakes and 11 mining (chemical) explosions recorded by the NORESS array in Norway. Preliminary results using this neural network method show very promising performance.<<ETX>>

Seismicity of the Great Lakes region

The Symposium on the Seismicity of the Great Lakes Region was held April 21, 1988, at the University of Akron, Ohio, in connection with the 22nd Annual Meeting of the North-Central Section of the Geological Society of America, sponsored by the Department of Geology, University of Akron. The purpose of this symposium was to reassess the seismicity of the region and its relationship to tectonic features in view of the unexpectedly strong earthquake of January 31, 1986, near the Perry nuclear power plant in northeast Ohio. A total of 13 papers were presented to an audience of about 60–70. Abstracts of these papers appear in Abstracts with Programs, Geological Society of America, volume 20, number 5, March 1988.