Possible Correlations between the ULF Geomagnetic Signature and Mw6.4 Coastal Earthquake, Albania, on 26 November 2019

Abstract

An earthquake of Mw6.4 hit the coastal zone of Albania on 26 November 2019, at 02:54:11 UTC. It was intensively felt at about 34 km away, in Tirana City, where damages and lives lost occurred. To emphasize a pre-seismic geomagnetic signature before the onset of this earthquake, the data collected on the interval 15 October–30 November 2019, at the Panagjurishte (PAG)-Bulgaria and Surlari (SUA)-Romania observatories were analyzed. Further on, for geomagnetic signal identification we used the polarization parameter (BPOL) which is time invariant in non-seismic conditions and it becomes unstable due to the strain effect related to the Mw6.4earthquake. Consequently, BPOL time series and its standard deviations are performed for the both sites using ultra low frequency (ULF)-fast Fourier transform (FFT) band-pass filtering. A statistical analysis, based on a standardized random variable equation, was applied to emphasize on the BPOL*(PAG) and ABS BPOL*(PAG) time series the anomalous signal’s singularity and, to differentiate the transient local anomalies due to the Mw6.4earthquake, from the internal and external parts of the geomagnetic field, taken PAG observatory as reference. Finally, the ABS BPOL*(PAG-SUA) time series were obtained on the interval 1–30 November 2019, where a geomagnetic signature greater than 2.0, was detected on 23 November and the lead time was 3 days before the onset of the Mw6.4earthquake.

Anomalous Geomagnetic Signal Emphasized before the Mw8.2 Coastal Alaska Earthquake, Occurred on 29 July 2021

“…The geomagnetic data (Bx, By and Bz) obtained, via internet ( ), from the geomagnetic observatories College (CMO) and Newport (NEW), on the interval 17 June–31 July 2021, are used: To carry out the daily mean distribution of the Polarization Parameter (BPOL) and its Standard Deviation (STDEV)—see formula on the web, Relation (1); To emphasize a possible pre-seismic geomagnetic signature related to the Mw8.2 earthquake, applying a statistical analysis based on relation (3) BPOL* = (X − Y)/W where: X is the value of the BPOL starting with 1 July 2021 till 31 July 2021, Y is 30 days running average of BPOL for consecutive days before a specific day, W is the same as Y but for STDEV obtained for 30 consecutive days before the specific day, BPOL* emphasizes the threshold for anomaly using STDEV. The explanation for (X, Y, W) and BPOL* may be seen detailed in [ 19 ]. To separate the pre-seismic anomalous signals from ionospheric and terrestrial variations of the geomagnetic field, the Relation (4) was applied, where the Newport geomagnetic observatory was taken as reference BPOL*(NEW-CMO) = (A − B)/C where: A represents the difference between BPOL NEW and BPOL CMO for a specific day, on the interval 7 July 2021–31 July 2021, B is 30 days running average of (BPOL NEW- BPOL CMO) before a specific day, C is 30 days running average of (STDEV NEW-STDEV CMO) before a specific day.…”

“…BPOL*(NEW-CMO) time series emphasizes the threshold for anomaly using STDEV. For more explanations for A, B and C in (4), see Reference [ 19 ].…”

“…The geomagnetic data (Bx, By and Bz) obtained, via internet (www.intermagnet.org), from the geomagnetic observatories College (CMO) and Newport (NEW), on the interval 17 June-31 July 2021, are used: where: X is the value of the BPOL starting with 1 July 2021 till 31 July 2021, Y is 30 days running average of BPOL for consecutive days before a specific day, W is the same as Y but for STDEV obtained for 30 consecutive days before the specific day, BPOL* emphasizes the threshold for anomaly using STDEV. The explanation for (X, Y, W) and BPOL* may be seen detailed in [19]. (c) To separate the pre-seismic anomalous signals from ionospheric and terrestrial variations of the geomagnetic field, the Relation (4) was applied, where the Newport geomagnetic observatory was taken as reference…”

“…Sci. USA 112, 986-989 (2015)] in advance by studying the spatiotemporal variations of the variability [Europhysics Letters (EPL) 91, 59001 (2010)] of the order parameter of seismicity in Japan [13]; earthquake prediction and precursor [14]; changes in the geoelectric conductivities, that in the real geophysical properties may generate internal electromagnetic effect [15][16][17][18][19][20]. All these mentioned research methods may supply more useful information about the origin of the different pre-seismic anomalous geomagnetic signals related to the major seismic events, what means a more conclusive separation of them.…”

Anomalous Geomagnetic Signal Emphasized Before the Mw8.2 Coastal Alaska Earthquake, Occurred on 29 July 2021

“…Starting around 2010 year, the geomagnetic monitoring investigations created the possibility to be elaborated a specific methodology that be able to emphasize certain inter-relations between the pre-seismic ultralow frequency (ULF) anomalous geomagnetic signature and a major seismic event occurrence [13]. To tackle this methodology some theoretical concepts concerning earthquake generation mechanism had to be taken into consideration, such as: piezomagnetic effect, magneto-hidrodinamic effect and electrokinetic effect [19]. Thus, in order to identify any pre-seismic anomalous signature related to Mw.8.2 earthquake we focused on two relations: a) Polarization parameter (BPOL) expressed as:…”