Dumitru Stanica 1 and Dragos Armand Stanica 1
1. Institute of Geodynamics of the Romanian Academy, Bucharest 37, Romania, RO 020032
Abstract
In seismogenic studies, the volatile transport is one of basic features of earthquake preparation and associated precursors’. According to [1], the degassing model of the Earth could be one of main factors controlling seismicity processes and energy transfer in the lithosphere. This model, based on laboratory experiments, includes the ascending diffusion effect of helium, hydrogen and possible other gases belonging to the crystalline structure of rocks. Another concept [2] related to which the most of rock forming the mineral composing lithosphere can emanate molecular hydrogen as result of the fracturing processes due to anhydrous minerals which must contain some water as impurity of OH- in their crystalline structures. Also, it is reasonable to suggest that in the Earth’s lithosphere, some well conducting channels (deep faults) do exist and may generate continuous intersecting geotectonic systems (sutures). Thus, the research on the relation between spatial-temporal changes of the electrical conductivity and seismic events has become an important subject in this direction, and the dehydration of the rocks, associated with rupturing processes and fluid migration through faulting systems acting as high sensitive path reflected by the CECA [3], could be detected by means of the anomalous behaviour of the electromagnetic
(EM) parameters carried out throughout the frequency range 10-2 Hz - DC [4 and 5]. In this respect, taking into account that the seismic-active Vrancea zone is one of the “hot” subjects, this paper is focused on a specific methodology able to emphasize the short–term EM precursory parameter, associated to intermediate depth earthquakes (EQ). According to the electromagnetic information acquired in a span of several years correlated with seismic events, it is relieved that:
(i) some days before an EQ occurred, the daily mean variation of the EM parameter has had an anomalous behaviour marked by a significant increase versus its normal distribution identified in non seismic conditions; (ii) the earthquakes are triggered during the instability period of the EM parameter and when the stability and instability periods are very closed, then corresponding domains are superimposed and its maximum value may or not correspond with the maximum magnitude of the earthquakes.
References
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[4] Stanica D., Stanica, M. Visan M., Popescu M., 2006, Anomalous behavior of the electromagnetic parameters associated to intermediate depth earthquakes. Rev. roum.
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[5] Stanica D., Stanica M., 2007, Electromagnetic monitoring in geodynamic active areas, Acta
Geodynamica et Geomaterialia, Vol.4, No. 1(145), Prague, 99-107