The earth’s crust is disappearing under California. The test is in its earthquakes

The border between the mantle and the land cortex is a region that attracts interest of numerous geologists. Being so close and so far from the reach of the instruments that these scientists use perhaps a certain mysticism to this region, but above all, because the dynamism of The interactions Among the outermost layers of our planet makes this border a specially active region at the geological level.

Scratching the bark. Now, a new study He has revealed A new aspect of this interaction. He has done it in the Sierra Nevada Californiana, or rather under this Sierra, where they have found evidence of how the mantle “pela” the earth’s crust.

Delamination Geologists believe that, from time to time, fragments of the lithosphere end up detaching themselves and sinking into the upper layers of the terrestrial mantle. This process is known as alamination or sinking of the lithosphere and could be responsible for the notable differences in the thickness of the oceanic crust in contrast to the continental cortex, among other characteristics of the geology and geography of the planet.

Generally, this process is seen as a “drip”: the heaviest rock of the cortex loses consistency and ends up detaching from the lithosphere to sink into the mantle, composed of less dense materials. However, Maybe this delamination is more abruptsomething like the terrestrial mantle “pelara” the cortex.

Seismic waves. As usual in this type of studies, the team analyzed the way in which seismic waves move through the interior layers of the Earth in order to study factors such as the composition and density of these layers. Sierra Nevada is a seismically active region, which implies a greater ease to compile data in this way.

The researchers responsible for the study They combined various sources of seismic data in their study, starting with this analysis, called the receiving function. The team combined it with the exhaustive catalog data of the Advanced National Seismic System (COMCAT). In this catalog they detected the presence of a “band of seismicity” in the region, located from 40 kilometers under the surface, which concentrated small earthquakes of magnitudes between 1.9 and 3.2.

Break, I don’t drip. Thanks to the differences detected through the receiving functions, the equipment was able to find a differentiated layer in the mantle, a not so differentiated layer as it extends to the north and that is consistent with the hypothesis that part of the lithosphere in the South Zone broke out of the cortex several million years ago.

The small earthquakes on the other hand, could be indicative that this detachment was made for breakage instead of drip, according to the authors of the study. The details of this analysis were published In an article In the magazine Geophysical Research Letters.

Strengthening the hypothesis. The evidence is not yet conclusive as the team admits, but they add to the already numerous that support the hypothesis that the discontinuity of Mohorovičić (the border between the cortex and the upper mantle of the earth) is not abrupt under the mountain range from Sierra Nevada, but rather gradual.

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