Abstract:
The subject of pre-earthquake ionospheric signatures has always been contentious and debatable.
Some of the previous reports have documented unforeseen and unusual variations in some of the
atmospheric and ionospheric parameters well before an earthquake. Here, we analyze the ionospheric
response from the Indian Subcontinent to Nepal Gorkha Earthquakes occurred between April and
May 2015, which were the most powerful and disastrous natural calamities in past ~80 years over
the Himalayan region left ~9000 causalities and more than ~20000 people injured with the property
damage of the order of several billion dollars. In view of severe earthquakes occurrences, their prior
information on the shorter time scales are warranted for mitigation of associated disasters. Here, we
report for the first time, a case which shows a strong link in anomalous variations between VLF subionospheric
signal and mesospheric ozone prior to both April 25, 2015 (Mw = 7.8) earthquake and its
biggest aftershock on May 12, 2015 (Mw = 7.3). Observations show an unusual variation in VLF signals
amplitude /shift in terminator time (TT) strongly linked with positive (negative) mesospheric ozone
anomaly in D-region altitudes prior to the Gorkha Nepal earthquakes. It is surmised that simultaneous
continuous observations of both VLF waves and mesospheric ozone can be considered as an important
tool to identify the prior earthquake signatures in the vicinity of the extremely earthquake-prone zone
such as Himalayan region. In this context, the current report opens up a new dimension in lithosphere atmosphere-
ionosphere coupling during the earthquake preparation processes itself.
