New seismic event

Cascadia subduction zone in the north-western United States (Figure authors work).

The earth trembles, not only because of volcanoes and earthquakes, friends. Scientists at Washington University (Seattle, USA) described in detail the recently discovered phenomenon called «deep concussion» (deep tremor).

Strictly speaking, this process should be called non-volcanic tremor. Previously it was thought that it induces a flow of magma beneath volcanoes. Now scientists know that this phenomenon is happening deep under the ground, long before the earthquake, in an area where two tectonic plates «scratch» each other.

Non-volcanic tremor is not as obvious as volcanic, and it had not paid any attention, taking the background noise in the seismic data. It is mainly characterized by long, but soft vibration — almost constant «grunt» deep inside the Earth. First, it drew the attention of Japanese researcher Kazusige Obara, speaking about his discovery in 2002.

With a more sensitive technique of deep seismic tremor found in subduction zones about 30 km underground. In these areas, the layers go one under the other and sink into the mantle. It is this transition and sliding layers and creates non-volcanic tremor. However, it remains debatable question about the exact location of a concussion and how it arises.

In subduction zones there are strong, destructive earthquakes, so an understanding of how there is a tremor, will allow scientists to develop an effective prevention tool. A deep observation of tremors may give valuable information about the movement and accumulation of layers of stresses along the tectonic faults.

The researchers believe that non-volcanic tremor affects not the amount of time when the layers rub against each other, and the hardness of the rocks in contact.

In the new study analyzed the deep tremors in the Nankai subduction zones in Japan, Cascadia in the north-western United States, Alaska, and in Costa Rica.

Results of the study are presented in the journal Nature   (PDF).

Source: Kompyulenta

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