The perturbation produced in the atmosphere/ionosphere associated with earthquake precursors during seismic activity of two major earthquakes which occurred on (1) 24 June 2019 in Indonesia (M = 7.3) and (2) on 19 August 2018 at Ndoi, Fiji (M = 8.2), are studied. Based on statistical analysis of total electron content (TEC) data, the presence of ionospheric perturbations 5 days before and after the main shock are found, which depends on the distance as well as direction of observation point from the epicentre. In general, ionospheric perturbations after the EQ at all the stations are found larger than that before the EQ. Probable mechanisms behind these perturbations associated with EQ are also being discussed. The ionospheric perturbations are observed at stations which are at larger distances from the epicentre, but not observed over other stations in different directions which are comparatively closer to the epicentre. These results suggest that seismic induced ionospheric anomaly is not isotropic in nature. Ozone data from three satellites: AIRS, OMI, and TOMS-like and MERRA-2 model are also analyzed 5 days before the EQ day and compared to the monthly average level. A strong link between anomalous variation in ionospheric TEC and atmospheric ozone data prior to both the EQs is noticed.

The information about the ongoing tectonic faulting process causing earthquakes in an area having single or sparse seismological waveform data available remains a mystery for seismologists. The usual P-wave polarity inversion is unable to find the solution to the earthquake mechanism if the event is recorded with a lower azimuthal coverage network. Recently some seismologists seek towards the moment tensor solution and tried to find the focal mechanisms of earthquakes. The present work is a step in the same direction. Twelve regional earthquakes recorded by a distant seismological network in the Siang region of Arunachal Himalaya have been analyzed using ISOLA codes developed by Sokos and Zahradnik (2008). The solutions obtained by CMT Harvard by inversion of a large number of available waveform data have been considered standards. In the present study, moment tensor solutions have been estimated using the hypocentre locations given by the CMT catalog. The obtained solutions are comparable with the CMT solutions reported. High variance reduction has been obtained for the analyzed earthquakes that agree with the observations by Delouis and Legrand (1999), Kim and Kraeva (1999), Kim et al. (2000), Dragger (2003), and Maercklin et al. (2011) that moment tensor solutions can be obtained by using single station waveform data. The present study infers that the moment tensor inversion would be useful for obtaining information about the ongoing faulting process for which limited waveform data is available. For most of the Himalayan earthquakes which occur northern side of the Main Central Thrust (MCT), the seismological networks in those areas are either very sparse or not instrumented at all. The knowledge of undergone tectonics of this region was established with various faults visible on the surface by geologists and lacks the knowledge of the present situation of ongoing tectonics of the region. Hence, the moment tensor solutions obtained using available data will help in understanding the ongoing tectonic processes of the regions lacking well coverage of seismological networks.