Coseismic Traveling Ionospheric Disturbances during the M_w 7.8 Gorkha, Nepal, Earthquake on 25 April 2015 From Ground and Spaceborne Observations

Abstract

Coseismic traveling ionospheric disturbances (CTIDs) and their propagation characteristics during Mw 7.8 Gorkha earthquake in Nepal on 25 April 2015 have been investigated using a suite of ground‐based GPS receivers and broadband seismometers along with the spaceborne radio occultation observations over the Indian subcontinent region. Depletion in vertical total electron content, a so called ionospheric hole, is observed near the epicenter ~9–11 min after the onset of earthquake. A positive pulse preceding the depletion, similar to N‐shaped perturbation, propagating with an apparent velocity of ~2.4 km/s is observed on the south. Further, the CTIDs in the southward direction are found to split in to fast (~2.4–1.7 km/s) and slow (~680–520 m/s) propagating modes at epicentral distances greater than ~800 km. However, the velocities of fast mode CTIDs are significantly smaller than the surface Rayleigh wave velocity (~3.7 km/s), indicating that they are not the true imprint of Rayleigh wave, instead, can probably be attributed to the superimposed wave front formed by the mixture of acoustic waves excited by main shock and propagating Rayleigh wave. The southward CTIDs are found to propagate at F2 region altitudes of ~300–440 km captured by Constellation Observing System for Meteorology, Ionosphere and Climate radio occultation observations. The CTIDs with periods of ~4–6 min are observed in all directions with significantly larger amplitudes and faster propagation velocities in south and east directions. The observed azimuthal asymmetry in the amplitudes and velocities of CTIDs are discussed in terms of the alignment with geomagnetic field and nature of surface crustal deformation during the earthquake.

Ionospheric Detection of Natural Hazards

“…The “splitting” of CSID into faster and slower modes was explained by the difference in their propagation speed. The occurrence of multiple modes was later confirmed for several other large earthquakes, including the great Tohoku‐oki earthquake of 11 March 2011 (e.g., Galvan et al, ; Jin et al, ; Kakinami et al, ; Liu et al, ; Rolland, Lognonné, Astafyeva, et al, ), the M7.8 April 2015 Nepal earthquake (Reddy & Seemala, ; Tulasi Ram et al, ), and the 2005 Northern California offshore earthquake (Jin, ). Figure b shows multiple‐mode CSID observed by Satellite G15 after the Tohoku‐oki earthquake observed by Galvan et al ().…”

Modeling of Ionospheric Responses to Atmospheric Acoustic and Gravity Waves Driven by the 2015 Nepal 7.8 Gorkha Earthquake

“…Tulasi Ram et al () reported TEC perturbations of 1.7 TECu (peak‐to‐peak), being stronger to east and south from epicenter. They also reported far‐field CIDs, observed to the south from the epicenter, propagating with phase velocities 1.73–2.39 km/s, but pointed to the inconsistency of the propagation velocities of these CIDs with RW group velocities calculated from seismometers data, which were reported as 3.4–3.7 km/s.…”

Upper Atmospheric Responses to Surface Disturbances: An Observational Perspective

“…Combinations of all the above observational techniques have also been applied to provide more complete 3‐D pictures of upper atmospheric responses to specific earthquakes (Hao et al, ; Liu et al, ). Earthquake‐induced perturbations in vertical electron density profiles have been retrieved using radio occultation measurements (Sun et al, ; Tulasi Ram et al, ). In addition, a few studies investigated in situ satellite observations of upper atmospheric neutral density perturbations in response to earthquakes (Garcia et al, ; Yang et al, ).…”