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Examination of seismo ionospheric anomalies before earthquakes of Mw ≥5.1 for the period 2008–2015 in Oaxaca, Mexico using GPS TEC

Melgarejo-Morales Angela, Vazquez-Becerra G. Esteban, Millan-Almaraz J. R., Pérez-Enríquez R., Martínez-Félix Carlos A., Gaxiola-Camacho J. Ramon

Acta Geophysica

2020

Vol. 68, no. 5

1229--1244

Earthquakes are a major danger in a constantly growing society due to their imminent impact and power of destruction. Therefore, the idea of successfully forecasting an earthquake continues to motivate the multidisciplinary study of phenomena proposed as possible earthquake precursors such as ionospheric anomalies. In that sense, total electron content (TEC) has demonstrated to be an efcient parameter for investigating the state of the ionosphere by making use of the Global Positioning System receivers. In the present study, raw vertical TEC data obtained from the standard RINEX fles of the GPS constellation are used to examine the state of the ionosphere during the occurrence of light to moderate earthquakes in Mexico from years 2008 to 2015 with the aim of search for possible ionospheric anomalies related to seismic activity. In order to evaluate the impact at the geomagnetic and ionospheric environments, the Geomagnetic Equatorial Dst index, which is considered to have a great infuence on TEC during geomagnetic storm period, and solar activity parameters, have been considered. The results indicated that 17 (74%) of the studied events presented not quiet geomagnetic conditions for the days before the earthquake. Thus, the changes in VTEC are most likely related to geomagnetic anomalies which rules out its possible seismic origin. Contrariwise, 3 (13%) of the events presented geomagnetic anomalies the days after the earthquake. For the remaining 3 (13%) events, these presented particular characteristics, such as: not quiet geomagnetic condition for the earthquake day, geomagnetic anomalies throughout the period and the opposite.

Anomalous Variations of Ionosphere Associated with the Strong Earthquake at Pakistan-Iran Border at a Low Latitude Station Agra, India

Pundhir D., Singh B., Singh O. P., Gupta S. K.

Acta Geophysica

2016

Vol. 64, no. 3

796--809

In this paper, we analyze the TEC data for April 2013 observed at Agra station, India (geogr. lat. 27.2° N, long. 78° E) to examine the effect of earthquake of magnitude M = 7.8 which occurred on 16 April 2013 at Pakistan–Iran border region. We process the TEC data using the σ statistical criterion to find out anomalous variation in TEC data. We also study the VLF propagation signal from NPM, Hawaii (21.42° N, 158° W), which is monitored at the same station (Agra station) in the light of this earthquake as well as solar flares. The nighttime fluctuation method is used to analyze the VLF data for the period of ±5 days from the day of earthquake (11-21 April 2013). The anomalous enhancements and depletions are found in TEC data on 1-9 days before the occurrence of event.