Abstract
In this paper we used the geomagnetic data, collected in real time on the intervals August- September and November-December, 2016, to emphasize possible relationships between the anomalous behavior of the normalized function Bzn and the both M5.7 and M5.6 earthquakes, generated at 72 km and, respectively 71 km depth, in the seismic active Vrancea zone on September 24 and December 28, 2016. Daily mean distributions of the Bzn and its standard deviation (SD) are obtained for the both time-intervals, in the ULF frequency range 0.001Hz - 0.0083Hz, by using the FFT band-pass filtering. We investigate the singularities of the pre-seismic anomalous signals related to the M5.7 and M5.6 earthquakes applying a statistical analysis based on a standardized random variable equation, and the results are presented as Bz* time series performed on the new time intervals 1-30 September and 1-31 December, 2016. Finally, two pre-seismic anomalous signals are observed: first one on September 21, with values greater than 5 SD, what means a lead time of 3 days before the onset of M5.7 earthquake; the second one, with values larger than 4 SD, which was identified on December 21 with 7 days prior to M5.6earhquake. In conclusion, as the work-station has specific programs for data processing, analyses and real time (daily) data display on the institute website, it may be used as an early warning system able to provide useful information for resilience improvement against the Vrancea intermediate depth seismicity.
Highlights
It is well known that the assessment of natural hazard and risk generally aims at analyzing potential impact of specific processes to a rather well balanced system, in order to emphasize to what extent it might be affected in the future
The origin of the ULF geomagnetic signal is not well-known yet, the following generation mechanisms may be considered: a) Magneto-hydrodynamic effect, which supposes that the conducting fluid flow, in the presence of a magnetic field, generates a secondary induced component [Sasay, 1991]; b) piezo-magnetic effect, based on the idea that a secondary magnetic field is induced by changes in ferromagnetic rocks magnetization, due to an applied stress [Fitterman, 1978]; c) Electrokinetic effect, based on electric currents flow at the interface solid-liquid boundaries, which in turn may generate a magnetic field [Fitterman, 1978; Varotsos at al., 1986]; d) Piezo-stimulated current and current generated by charged dislocation [Varotsos at al., 1986]
On the interval September 19-26, a significant anomalous domain of minimum, with values ranging from 1.933 to about 1.942 is observed on Bzn distribution (Figure 3). This anomaly is generated by the increased value of B┴ (Figure 4), due to the high stress reached in Vrancea seismogenic volume, followed by the released electrical charges that are propagated along the 2-D geoelectric structure (CECA), before the onset of the Mw 5.7 earthquakes
Summary
It is well known that the assessment of natural hazard and risk generally aims at analyzing potential impact of specific processes to a rather well balanced system, in order to emphasize to what extent it might be affected in the future. The origin of the ULF geomagnetic signal is not well-known yet, the following generation mechanisms may be considered: a) Magneto-hydrodynamic effect, which supposes that the conducting fluid flow, in the presence of a magnetic field, generates a secondary induced component [Sasay, 1991]; b) piezo-magnetic effect, based on the idea that a secondary magnetic field is induced by changes in ferromagnetic rocks magnetization, due to an applied stress [Fitterman, 1978]; c) Electrokinetic effect, based on electric currents flow at the interface solid-liquid boundaries, which in turn may generate a magnetic field [Fitterman, 1978; Varotsos at al., 1986]; d) Piezo-stimulated current and current generated by charged dislocation [Varotsos at al., 1986] Another concept [Freund, et al.,1999, Freund, 2000], according to which the most of rock forming the mineral composing lithosphere can emanate molecular hydrogen, as result of the impurity of OH- in their crystalline structures. In this paper some innovative contributions to the resilience improvement against the intermediate depth earthquakes by using EM methodology will be promoted
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