Τίτλος:
On Possible Electromagnetic Precursors to a Significant Earthquake
(Mw=6.3) Occurred in Lesvos (Greece) on 12 June 2017
Γλώσσες Τεκμηρίου:
Αγγλικά
Περίληψη:
This paper reports an attempt to use ultra-low-frequency (ULF) magnetic
field data from a space weather monitoring magnetometer array in the
study of earthquake (EQ) precursors in Greece. The data from four
magnetometer stations of the HellENIc GeoMagnetic Array (ENIGMA) have
been analyzed in the search for possible precursors to a strong EQ that
occurred south of Lesvos Island on 12 June 2017, with magnitude Mw = 6.3
and focal depth = 12 km. The analysis includes conventional statistical
methods, as well as criticality analysis, using two independent methods,
the natural time (NT) method and the method of critical fluctuations
(MCF). In terms of conventional statistical methods, it is found that
the most convincing ULF precursor was observed in the data of ULF (20-30
mHz) depression (depression of the horizontal component of the magnetic
field), which is indicative of lower ionospheric perturbation just 1 day
before the EQ. Additionally, there are indications of a precursor in the
direct ULF emission from the lithosphere 4 days to 1 day before the EQ.
Further study in terms of NT analysis identifies criticality
characteristics from 8 to 2 days before the EQ both for lithospheric ULF
emission and ULF depression, while MCF reveals indications of
criticality in all recorded magnetic field components, extending from 10
to 3 days before the EQ. Beyond the recordings of the geomagnetic
stations of ENIGMA, the recordings of the fracto-electromagnetic
emission stations of the HELlenic Seismo-ElectroMagnetics Network
(ELSEM-Net) in Greece have been analyzed. The MHz recordings at the
station that is located on Lesvos Island presented criticality
characteristics (by means of both NT analysis and MCF) 11 days before
the EQ, while a few days later (7-6 days before the EQ), the kHz
recordings of the same station presented tricritical behavior. It is
noted that the magnetosphere was quiet for a period of two weeks before
the EQ and including its occurrence.
Συγγραφείς:
Potirakis, Stelios M.
Schekotov, Alexander
Contoyiannis, Yiannis
and Balasis, Georgios
Koulouras, Grigorios E.
Melis, Nikolaos S.
and Boutsi, Adamantia Zoe
Hayakawa, Masashi
Eftaxias,
Konstantinos
Nomicos, Constantinos
Λέξεις-κλειδιά:
The 2017 Lesvos earthquake (EQ); ultra-low-frequency (ULF) effects; EQ
precursor; lithospheric ULF emission; ULF depression;
fracto-electromagnetic emissions
