Abstract
On May 14, 2019, a strong Mw = 7.6 shallow earthquake occurred in Papua New Guinea. This paper explores for the first time the analysis of total electron content (TEC) products measured for 6 months by GPS antenna onboard Swarm satellites, to detect possible seismo-ionospheric anomalies around the time and location of the above-mentioned earthquake. The night-time vertical total electron content (VTEC) time series measured using Swarm satellites Alpha and Charlie, inside the earthquake Dobrovolsky’s area show striking anomalies 31 and 35 days before the event. We successfully verified the possible presence of concomitant anomalous values of in situ electron density detected by the new Chinese satellite dedicated to search for electromagnetic earthquake precursors [China Seismo-Electromagnetic Satellite (CSES)-01]. On the other hand, the analysis of VTEC night time measured by Swarm Bravo shows gradual and abnormal increase of the VTEC parameter from about 23 days before the earthquake, which descends 3 days before the earthquake and reaches its lowest level around the earthquake day. We also analyzed the time series and tracks of other six in situ parameters measured by Swarm satellites, electron density from CSES, and also GPS-TEC measurements. As it is expected from the theory, the electron density anomalous variations acknowledge the Swarm VTEC anomalies, confirming that those anomalies are real and not an artifact of the analysis. The comparative analysis with measurements of other Swarm and CSES sensors emphasizes striking anomalies about 2.5 weeks before the event, with a clear pattern of the whole anomalies typical of a critical system as the earthquake process is for Earth. A confutation analysis outside the Dobrovolsky area and without significant seismicity shows no anomalies. Therefore based on our study, the VTEC products of Swarm satellites could be an appropriate precursor aside from the other measured plasma and magnetic parameters using Alpha, Bravo, and Charlie Swarm and CSES satellites that can be simultaneously analyzed to reduce the overall uncertainty.
Highlights
Since the seismological community generally emphasizes the great difficulty of earthquake prediction by analyzing seismic data (e.g., Matsumura, 2009), or even the impossibility of such an enterprise (e.g., Geller, 1997), many researchers have dedicated their efforts to search for alternative non-seismic precursors
Swarm mission is a constellation of three identical satellites, Alpha (A), Bravo (B), and Charlie (C), placed in quasi-polar orbits at an altitude between 440 (Alpha and Charlie) and 510 km (Bravo) (FriisChristensen et al, 2006). These satellites include magnetic and plasma sensors: 1) an absolute scalar magnetometer (ASM), which measures the strength of the magnetic field and provides scalar measurements of the magnetic field to calibrate the vector field magnetometer; 2) a vector field magnetometer (VFM), which makes high-precision measurements of the intensity and direction of the magnetic field; and 3) the EFI instrument, which is composed of the Langmuir probe and thermal ion imager
Even if we propose a link of this depletion of electrons with the impending earthquake, we need to note that it happened between two geomagnetically disturbed periods, so even an external perturbation of the ionosphere can be the source of this phenomenon
Summary
Since the seismological community generally emphasizes the great difficulty of earthquake prediction by analyzing seismic data (e.g., Matsumura, 2009), or even the impossibility of such an enterprise (e.g., Geller, 1997), many researchers have dedicated their efforts to search for alternative non-seismic precursors. These conditions have been applied, taking into account two ways of possible magnetosphere–ionosphere coupling: one is the impact of solar wind onto the ionosphere, and the other is the electromagnetic field coupling For the former, the time of flight of the particles from ACE satellite to Swarm or CSES has been estimated for the specific time while for the latter, it requires about 5 s so it can be considered instantaneous for this work. This time series indicates other unusual variations 4, 13, and 31 days before the earthquake with the deviation values of 8.27%, 29.32%, and −74.68%, respectively. The VTEC night-time variations measured by Swarm C acknowledge the observed anomalies by Swarm A on 31 and 35 days prior to the earthquake (Supplementary Figure S1)
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