1973. American Geological Institute, Geological Survey (U.S.), Environmental Systems Research Institute (Redlands, Calif.), National Earthquake Information Center, and National Geophysical Data Center. This datalayer is a point coverage representing earthquake epicenters (1973 through March, 2003). Historical data for this layer were derived from:... American Geological Institute.
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Geological Survey (U.S.), National Geophysical Data Center, and National Earthquake Information Center. This shapefile includes points which represent locations of significant historical earthquakes worldwide documented from 2150 B.C. until 1994 A.D. ... American Geological Institute.
2010. National Geophysical Data Center. This map layer shows isogonic lines (lines of constant declination of the Earth's magnetic field), derived from the International Geomagnetic Refer... National Atlas of the United States.
2010. National Geophysical Data Center. This line shapefile shows lines of equal horizontal intensity of the Earth's magnetic field, derived from the International Geomagnetic Reference F... National Atlas of the United States.
2010. National Geophysical Data Center. This shapefile shows isoclinic lines (lines of constant inclination of the Earth's magnetic field), derived from the International Geomagnetic Refe... National Atlas of the United States.
2010. National Geophysical Data Center. This map layer shows isoporic lines (lines of equal annual change, or secular variation, in the declination of the Earth's magnetic field), derived... National Atlas of the United States.
2010. National Geophysical Data Center. This line shapefile shows lines of equal annual change (secular variation) in the horizontal component of the total field intensity of the Earth's ... National Atlas of the United States.
2010. National Geophysical Data Center. This shapefile shows lines of equal annual change (secular variation) in the inclination of the Earth's magnetic field, derived from the Internatio... National Atlas of the United States.
2010. National Geophysical Data Center. This line shapefile shows lines of equal annual change (secular variation), in the total field intensity of the Earth's magnetic field, derived fro... National Atlas of the United States.
2010. National Geophysical Data Center. This line shapefile shows lines of equal annual change (secular variation) in the vertical component of the total field intensity of the Earth's ma... National Atlas of the United States.