March 13, 2012

GOCE Mapping Layer Between Earth’s Crust And Mantle

The ESA´s GOCE satellite has produced the first global high-resolution map of the boundary between the Earth´s mantle and its crust, according to an ESA press release.

Understanding the mantle-or MoHo-could provide us with clues about the Earth´s interior.

The Earth´s crust makes up only 1% total volume of our planet and is just the outermost shell. However, this 1% is very important to the overall makeup of the Earth. Geological resources such as oil and minerals are found in the crust, as well as natural gas. The crust also plays host to many geological processes such as volcano eruptions and earthquakes.

MoHo is derived from the word Mohorovičić Discontinuity and describes the boundary between the crust and the mantle. Discovered in 1909 by Croatian Seismologist Andrija Mohorovicic, the MoHo has been found to shift and change in not only depth below the crust but also in the velocity at which it moves. The word “discontinuity” is used for a surface where seismic waves change velocity. The depth of one of these surfaces below the ocean basin is an average of 8km deep, while the average depth below the continents is 32 km deep. At this discontinuity, the seismic waves accelerate.

Until now, all of what scientists knew of the deep levels of the earth came from gravimetric and seismic methods.

Seismic methods are based on the aforementioned seismic waves that move below the Earth´s surface.

Gravimetry is focused on the gravitational effect and density difference caused by the ever changing composition of crust and mantle.

The new MoHo models far exceed those previous models based on seismic and gravimetric study.

By producing the first high-resolution global map of the MoHo, the GOCE Exploitation for MoHo Modeling and Applications project (GEMMA) plan to study the way the ocean moves and circulates. By understanding more about ocean circulation, scientists hope to learn more about the Earth´s interior, as well as changes in sea-level and the way energy is exchanged globally via oceanic movement.

By using the inversion of homogenous gravimetric data, the GEMMA MoHo map is able to estimate MoHo depth globally, even in areas where ground data is not accurately available.

This new map will also give scientists clues about gravitational density around the globe.

The ESA´s GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite was launched in 2009. Since that time, it has been used to measure ocean circulation as well as gravitational variations. By flying as close to the Earth as possible-as low as 260 km high-the GOCE is more sensitive to Earth´s gravity field. Less than a year ago, the GOCE also delivered ground breaking, high resolution images of the variations in Earth´s gravity. By collecting more data and producing more high resolution images, the ESA hopes the GOCE will continue to shed light on the mysteries of Earth´s gravitational pull, ocean circulation and what lies below the Earth´s crust.


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