Cascadia subduction zone in the north-western United States (Figure authors work).
The earth trembles, not only because of volcanoes and earthquakes, friends. Scientists of the University of Washington (Seattle, USA) for details about 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 is the flow of magma beneath volcanoes. Now scientists know that this phenomenon occurs deep in 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 he had not paid attention, taking the background noise in the seismic data. It is characterized mainly by long but soft vibration — almost constant "grunt" deep inside the Earth. First, it drew the attention of Japanese researcher Kazusige Obara, who told of his discovery in 2002.
With a more sensitive technique of deep seismic tremor detected 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 a non-volcanic tremor. However, a matter of debate on the exact location of the shock and how it occurs.
In subduction zones 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 on the movement of formation and accumulation of stresses along the tectonic faults.
Researchers believe that the non-volcanic tremor affects not the amount of time when one of the layers rub against another, and the hardness of contact rocks.
In the new study analyzed the deep tremors in Nankai subduction zones in Japan, Cascadia in the north-western United States, Alaska, and in Costa Rica.
Results of the study presented in the journal Nature (PDF).