1ος παγκόσμιος χάρτης μαγνητικής ανωμαλίας

[evripidis]

Εκδόθηκε ο 1ος παγκόσμιος χάρτης μαγνητικής ανωμαλίας του πλανήτη μας, έπειτα από 50+ χρόνια ερευνών και από διάφορες πηγές.

Από την Commision for the Geological map of the World (CGMW) που εκδίδει και τον χάρτη :
" This map is the first global compilation of the wealth of magnetic anomaly information derived from more than 50 years of aeromagnetic surveys over land areas, research vessel magnetometer traverses at sea, and observations from earth-orbiting satellites, supplemented by anomaly values derived from oceanic crustal ages.
The objective is to provide an interpretive dimension to surface observations of the Earth’s composition and geologic structure. Metamorphism, petrology, and redox state all have important effects on the magnetism of crustal materials. "

Τον χάρτη μπορείτε να τον προμηθευτείτε από το παρακάτω link σε pdf μορφή.

ΧΑΡΤΗΣ



Ο project manager, Dr J Derek Fairhead, αναφέρει :

"Many of the companies and country organisations who hold the data in a confidential mode have been prepared to release 'decimated versions' of their data so that the commerciality of the data isn't affected.

"But the regional nature of the magnetic field can be clearly imaged and put together with all the other data to generate a global image of the magnetics."


Επίσης ένας από τους κορυφαίους ερευνητές του project, ο Dr Juha Korhonen από την ερευνητική ομάδα της Φινλανδίας, εξηγεί γιατι ο χάρτης είναι σε τέτοια ανάλυση:

"It represents a square grid of about five kilometres, so it's very coarse indeed. It is a starting point, and to go into detail, you can contact those organisations who have more detailed data on both the geology and mineral sources.

"There are just a few major deposits that can be seen on this map, like the Kursk iron ore deposit. Mainly one can see the major geological formations.

"It's generally considered in prospecting and resource analysis that this magnetic anomaly field is one of the most valuable tools or regional assets."



Σχετικά με τον χάρτη :

"The global map shows the variation in strength of the magnetic field after the Earth's dipole field has been removed (Earth's dipole field varies from 35,000 nanoTesla (nT) at the Equator to 70,000 nT at the poles). After removal of the dipole field, the remaining variations in the field (few hundreds of nT) are due to changes in the magnetic properties of the crustal rocks.

Hot colours (reds) indicate high values; cold colours (blues) indicate low or negative values."


"There are several different causes of magnetic anomalies in the Earth's crust.

On the ocean sea bed, the map shows a striped effect. Where Earth's tectonic plates are moving apart, new crust is created at mid-ocean ridges.

As the new material spreads out and cools, minerals in the rocks that make up the crust are magnetised in the direction of the Earth's magnetic field at the time of their formation. This field reverses polarity over time, creating alternating stripes on either side of the ridge."


"On land, the dominant factors for magnetic anomalies are the thickness of the magnetised layer and the composition of the crust. Usually, young crust is relatively thin and has a low content in magnetic minerals.

"Τhe old cratons, stable interior sections of the continental crust, are thicker and have high magnetic mineral content. Perhaps the most prominent feature is the Kursk anomaly, which can be seen at the border between young western Europe and the old "Baltic Shield"."