Abstract
The present paper reports the modification in GPS TEC (total electron content) and atmospheric refractivity prior to the Iran earthquake that had occurred on 16 April 2013 in Iran (28.10°N, 62.05°E). The analysis of GPS-based TEC from two GPS receivers, Surat (21.16°N, 72.78°E) and Lucknow (26.91°N, 80.95°E ) and results of atmospheric refractivity profile for radiosonde observation stations (Shiraz, Iran and Delhi, India) around the fault line are presented in this paper. It is seen that atmospheric refractivity gets modified from 8 to 6 days prior to the earthquake at Shiraz, Iran and Delhi, India. The GPS TEC showed variations a few days prior to the earthquake. We conclude that in search of precursory signatures for an earthquake, both GPS TEC and refractivity are important parameters.
Highlights
A major earthquake (M = 7.8) struck Iran near the border with Pakistan on 16 April 2013 at 10:44 GMT
In order to investigate that the modification in the GPS signal is caused due to sudden changes in atmospheric refractivity, its profile is obtained from the radiosonde observations
In order to attempt to identify earthquake-induced imprints on TEC profiles, it is necessary to have knowledge on the relation of TEC with solar and geomagnetic parameters; we show in Figure 2 the variation in Dst-index for the month of April 2013
Summary
Tremors from this earthquake were felt in India This made us do some intriguing research about whether large earthquakes are associated with ionospheric/atmospheric changes caused due to earthquake preparation above the epicenter or throughout the fault line. With respect to the earthquake preparation the vertical profiles of humidity, pressure and temperature are changed These variations in the local parameters cause the atmospheric refractivity to change and can potentially affect the ray path of any electromagnetic wave. Fujiwara and colleagues monitored the VHF waves (FM radio; around 80 megahertz) in eastern Tokyo that were transmitted from an over-the horizon radio station in northern Honshu, and thoroughly compared the waves with the seismicity in the surrounding regions They found that the transmission anomalies were significantly enhanced within five days prior to M ≥ 4.8 earthquakes. In order to investigate that the modification in the GPS signal is caused due to sudden changes in atmospheric refractivity, its profile is obtained from the radiosonde observations
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