Co-seismic ionospheric GPS-TEC disturbances from different source characteristic earthquakes in the Himalaya and the adjoining regions

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Abstract

Co-seismic ionospheric disturbances (CIDs) due to different source characteristic earthquakes are investigated through GPS-derived vertical total electron content (VTEC). We investigated VTEC changes related with Moderate, Strong, Major and Great earthquakes occurred at different tectonic settings in both Himalaya and non-Himalayan regions. The VTEC and its anomalies are computed using GPS data obtained from the local network of GPS stations in Himalaya with the IGS stations surrounding the epicentre region. Irrespective of the source characteristics, significant CIDs are observed during Major and Great earthquakes, namely; (i) the Mw 7.8, 25th April 2015 Gorkha earthquake, (ii) the Mw 7.6, 8th October 2005 Kashmir earthquake, and (iii) the Mw 8.6, 28th March 2005 Nias–Simeulue earthquake.
The VTEC anomalies due to the Gorkha event are observed 21.15min after the earthquake origin time and continued till 22.78min with the amplitude range from −0.530 to 0.517 (±0.11) TECU. CIDs associated with the Kashmir earthquake are noticed only at two GPS sites (NADI and PAN2) roughly after 23min of the earthquake occurrence. But, it continued around 14min with the amplitude range from −0.12 to 0.177 TECU (±0.02 TECU=1σ). However, for the case of Ocean-Island Arc Nias–Simeulue earthquake, anomalous CIDs were observed only at GPS site NTUS, where the disturbances started around 25.58min later and continued around 17.92min with amplitude range from −0.077 to 0.058 TECU (±0.02 TECU=1σ). We inferred that the CIDs originated because of earthquakes in Himalaya have relatively larger VTEC magnitudes (>15 TECU) that propagates faster in reaching and registering in the ionospheric layers compared with the non-Himalayan earthquakes. Secondly, different lithospheric-ionospheric coupling mechanism is operating in transferring the seismic energy, which originated from the Continent-Continent and the Tsunami genic Ocean-Island Arc collision zone, to the ionosphere.

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NRIAG Journal of Astronomy and Geophysics
Volume 7, Issue 2
December 2018
Pages 237-246

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