Two‐mode ionospheric response and Rayleigh wave group velocity distribution reckoned from GPS measurement following Mw 7.8 Nepal earthquake on 25 April 2015

The coseismic-induced ionospheric total electron content (TEC) perturbations were analyzed following the M-w 7.8 Nepal earthquake (28.147 degrees N, 84.708 degrees E; depth similar to 15km) that occurred on 25 April 2015 at 06:11:26 UTC. The ionospheric response is due to both the modes, i.e., shock acoustic waves (slow mode) and Rayleigh wave induced (fast mode). The continuous Global Positioning System (GPS) data at about 60 sites from various GPS networks have been used in the present study. All the sites within epicentral distance of similar to 2400km and 70 degrees-170 degrees azimuth recorded the Rayleigh wave-induced TEC response, while the sites within similar to 400-2200km in the same azimuth recorded the response from both the modes. The maximum coseismic-induced peak-to-peak TEC amplitude is similar to 1.2 total electron content unit, 1TECU=10(16)elm(-2). From Hodochron plot, the apparent Rayleigh wave velocity has been determined as similar to 2400m/s on the average and the acoustic wave velocity as 1180m/s, both these waves being discernible beyond similar to 1200km of epicentral distance as also evident from Hodochron plot and wavelet spectrographs. We reckoned the Rayleigh wave group velocities using ionospheric response at selected radial pairs of stations and validated. The ionospheric response distribution seen mainly depending on the epicentral distance, satellite geometry, directivity of radiation pattern, and the upper crustal heterogeneity. This study highlights the characteristics of ionospheric response consequent to the 2015 Nepal earthquake.