EMAG2: Earth Magnetic Anomaly Grid (2-arc-minute resolution)
EMAG2 is compiled from
satellite,
ship, and airborne magnetic measurements. Magnetic anomalies result from geologic features enhancing or depressing the local magnetic field. These maps increase knowledge of subsurface structure and composition of the Earth's crust. Global magnetic anomaly grids are used for resource exploration, navigation where GPS is unavailable (submarine, directional drilling, etc.), and for studying the evolution of the lithosphere.
The latest
EMAG2 (v3) includes more than 11.5 M new ship and airborne trackline data, and several new or updated precompiled grids. While the previous
EMAG2 relied on known or idealized local geology to interpolate anomalies into non-existent data areas, EMAG2 v3 relies solely on the data available. As a result, EMAG2 v3 better represents the complexity of these anomalies (particularly in oceanic regions) and accurately reflects areas where no data has been collected. The current version reports anomalies in two ways:
A consistent altitude of 4km (referred to as Upward Continued)
Anomaly altitude at Sea Level above oceanic regions and 4km above continental regions (referred to as
Sea Level)
EMAG2_V3 is delivered as a 1.5GB zip file that contains comma delimited data (CSV). The format descriptor is a text file that provides information about the CSV file.
The Code Map provides a reference to the primary data source for each cell as described in the Format file above. The Error Map displays the error associated with each grid cell.
This version (2009) is a significant update over our first global magnetic anomaly grid, EMAG3. It relies on ocean age models to directionally grid anomaly data into areas where no data exists. The grid is reported at an altitude of 4km.
This version (2007) is a 3 arc-minute resolution magnetic anomaly map. It was the NGDC (now NCEI) candidate for the World Digital Magnetic Anomaly Map at 5km altitude.
The global magnetic map illustrates Earth evolution (plate tectonics and crustal interaction with the deep mantle).
Distinct patterns and magnetic signatures are attributed to the formation (seafloor spreading) and destruction (subduction zones) of oceanic crust, and the formation of continental crust by accretion of various terrains to cratonic areas and large scale volcanism (both on continents and oceans).
Features
Magnetization is weaker at the equator and stronger at high latitudes, reflecting the strength of the ambient geomagnetic field, which induces magnetization in 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
