EMAG2: Earth Magnetic Anomaly Grid in 2-arc-minute resolution

Description:

While the largest portion of the Earth's magnetic field is generated in the Earth's core, magnetized rocks in the crust and upper mantle also make a significant contribution, called the "lithospheric magnetic field". Displayed in red-to-purple are areas where the lithospheric field points in the same direction as the core field, creating a "positive anomaly". Where the lithospheric field opposes the core field we see a "negative anomaly", displayed in blue-to-black. Yellow, white and light-blue indicate areas in which the lithospheric field is either very weak, or its direction is perpendicular to the (stronger) core field.

The magnetization of the lithosphere is due to iron minerals. Only at temperatures below 600 C are these minerals magnetic. This has two interesting consequences: (1) Only the outer 10 km to 50 km of the Earth is magnetized because temperatures exceed 600 C below this outer layer. (2) New crust is formed at a rate of a few centimeters per year at the mid ocean ridges. In this process, magnetic minerals cool from high temperatures to below 600 C and are magnetized in the direction of the surrounding magnetic field. Thus, a stripe of uniformly magnetized crust is formed on each side of the ridge axis. Every few hundred thousand years the core field reverses direction, and the next set of stripes therefore acquires the opposite direction of magnetization. This is clearly visible in EMAG2 as striped patterns which are symmetric about the ridge axis. Indeed, the discovery in the 1950s of these symmetric magnetic patterns provided the first indisputable evidence of continental drift.

EMAG2 is a global 2-arc-minute resolution grid of the anomaly of the magnetic intensity at an altitude of 4 km above mean sea level. It was compiled from satellite, marine, aeromagnetic and ground magnetic surveys.

For more information, visit the EMAG2 website.

Notable Features:

Magnetization is weaker at the equator and stronger at high latitudes, reflecting the strength of the ambient geomagnetic field, which induces the magnetization in the rocks
Stripes of alternating magnetization in the oceans are due to sea floor spreading and the alternating polarity of the geomagnetic field
Very old crust (North American Shield, Baltic Shield, Siberian Craton) have strongest magnetization, seen as dark shades of purple and blue
Areas with no data coverage are shown in gray

Data Category

Major: Land

Keywords:

Land, magnetism, anomaly, plate tectonics

Data Set Name	EMAG2 with iso lines black
Data Set Directory Name	emag2
Data Set Source	NOAA NGDC
Data Set Developer	Stefan Maus and Jesse Varner, NOAA NGDC
Visualization Developer	Stefan Maus and Jesse Varner, NOAA NGDC
Audio	No
Download	FTP
Date Added	April 2010

Maus, S., U. Barckhausen, H. Berkenbosch, N. Bournas, J. Brozena,V. Childers, F. Dostaler, J. D. Fairhead, C. Finn, R. R. B. von Frese, C. Gaina, S. Golynsky, R. Kucks, H. LÃ¼hr, P. Milligan, S. Mogren, R. D. MÃ¼ller, O. Olesen, M. Pilkington, R. Saltus, B. Schreckenberger, E. ThÃ©bault, and F. Caratori Tontini, EMAG2: A 2â€“arc min resolution Earth Magnetic Anomaly Grid compiled from satellite, airborne, and marine magnetic measurements, Geochem. Geophys. Geosyst., 10, Q08005, doi:10.1029/2009GC002471, 2009