Two-mode ionospheric response and Rayleighwave group velocity distribution reckonedfrom GPS measurement following Mw7.8 Nepal earthquake on 25 April 2015

Abstract

The coseismic-induced ionospheric total electron content (TEC) perturbations were analyzedfol lowing the Mw7.8 Nepal earthquake (28.147°N, 84.708°E; depth ~15 km) that occurred on 25 April 2015 at06:11:26 UTC. The ionospheric response is due to both the modes, i.e., shock acoustic waves (slow mode) andRayleigh wave induced (fast mode). The continuous Global Positioning System (GPS) data at about 60 sites fromvarious GPS networks have been used in the present study. All the sites within epicentral distance of ~2400 kmand 70°–170° azimuth recorded the Rayleigh wave-induced TEC response, while the sites within ~400–2200 kmin the same azimuth recorded the response from both the modes. The maximum coseismic-inducedpeak-to-peak TEC amplitude is ~1.2 total electron content unit, 1 TECU = 1016el m2. From Hodochron plot, theapparent Rayleigh wave velocity has been determined as ~2400 m/s on the average and the acoustic wavevelocity as 1180 m/s, both these waves being discernible beyond ~1200 km of epicentral distance as alsoevident from Hodochron plot and wavelet spectrographs. We reckoned the Rayleigh wave group velocitiesusing ionospheric respo nse at selected radial pairs o f stations and validated. The ionospheric res ponsedistribution seen mainly depending on the epicentral distance, satellite geometry, directivity of radiationpattern, and the upper crustal heterogeneity. This study highlights the characteristics of ionospheric responseconsequent to the 2015 Nepal earthquake.