A NEW GEOLOGICAL/GEOPHYSICAL TOOL: THE REVISED NORTH AMERICAN GRAVITY DATABASE

Recognizing the need for improved regional gravity databases, an international effort by governmental agencies, universities, professional organizations, and private industry is underway to update the publicly available North American Gravity Database. The current database that was released roughly two decades ago needs revision to improve its overall quality, coverage, observation density, and versatility. Considerable data have been made available in the intervening period and improvements are possible in the calculation of gravity anomalies by taking advantage of available terrain and geodetic models and high-speed data processing procedures and facilities. Data will be made available in a web-based system as part of the U.S. Geoinformatics initiative and through other governmental agencies. The goal of the Geoinformatics initiative is a fully integrated data system that has software for accessing and processing the data, including mapping, profiling, modeling, and filtering and that provides useful tutorials. The database will have a comprehensive menu making it useful for those with differing scientific interests and backgrounds. The user will be able to select desired corrections to the gravity data, units used, datums employed, and type of gravity anomaly and retrieve information on the predicted errors in the data. The default gravity anomalies (in milligals) of the database based on internationally accepted datums and constants will be useful for geological studies and most geophysical investigations. In contrast to the current U.S. gravity database the preferred (default) vertical datum for the gravity correction calculations is the Earth’s ellipsoid rather than the geoid (sea level), although users of the database may select an option that uses the geoid as the vertical datum. The difference in the gravity anomalies calculated using the ellipsoid vertical datum rather than the geoid will be negligible to most users. Database fields and formats will accommodate the increasingly available high-resolution, airborne, satellite, marine, and gradient gravity data and will be updated as additional data are obtained and improvements are made in data processing.