A protocol is presented to perform bulk magnetic susceptibility (BMS) analysis of simulated seawater/saline water using MFK2-FA Multi-Function Kappabridge instrument at Laboratory for Analyses of Magnetic and Petrofabric (LAMP), BHU to obtain a correlation between BMS and hydrogeological data such as salinity and conductivity. This LAMP-BHU Protocol involves the preparation of simulated saline water. It has been developed after BMS measurement of 20 simulated seawater samples in different frequencies, i.e., F1 (976 Hz), F2 (3904 Hz), and F3 (15616 Hz) to prepare a standard data. This standard data is further validated with field data. Fourteen water samples are collected from the field, and hydrogeological data (salinity and conductivity) and BMS at three different frequencies were measured. Further linear regression analysis is performed on the measured data. This protocol yields efficient results with F3, followed by F1 and F2 having an R$^{2}$ value of 0.84, 0.60, and 0.54, respectively, for salinity, and 0.79, 0.51, and 0.40, respectively, for conductivity. Salinity and conductivity are showing a negative trend with all the frequencies. This protocol enables to delineate saline water intruded zone or extent of saline intrusion using BMS analysis. The proposed protocol is a rapid and efficient mode of determination of the saline water intruded zones in the coastal aquifers for prioritisation of groundwater assets facilitating freshwater availability in coastal areas.

$\bf{Highlights}$

$\bullet$ Protocol is developed for Saline water intrusion studies using magnetic susceptibility measurements.

$\bullet$ Magnetic susceptibility, salinity and conductivity was measured for simulated and field samples.

$\bullet$ Inverse relationship observed between magnetic susceptibility w.r.t. salinity and conductivity.

$\bullet$ High frequency magnetic susceptibility provides better results for gradual increase in salinity.

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.

Barren Island volcano (BIV), India has started erupting vigorously from 2018 after a gap of 13 years (last active period 2004–2005) just after the 2004 tsunami. Although there is evidence of coupling between seismicity and earthquake in this region, it is not thoroughly researched. Here, we present satellite-based approach to monitor and understand the volcano dynamics w.r.t. associated seismicity at BIV using multispectral datasets, ${\sim}$ 20 yrs Volcanic Radiative Power (VRP) and ${\sim}$ 70 yrs historical earthquake data (1950–2020 July). The rate of frequency of earthquake has increased to 3.54 times during 1990–2020 as compared with 1950–1989 which signifies seismicity-induced pressure release that may have caused decompression in the region, leading to eruptions or at least modulation of the eruption. The VRP results clearly depicted the changes from low to high thermal regimes that indicate switching from open-vent to effusive activity of Barren Island volcano. The historical data of recent times show correlation of seismic and volcanic activities. The spatial-temporal distributions of earthquake swarm are not associated with volcano, but are clustered near the tectonic regimes. The volcanic activity is preceded by seismic activity along the regional tectonic structures. In addition, the 2018 eruptive phase has been analyzed for better understanding of the proposed event. The present research has provided significant supportive evidences to give adequate credence to this emerging hypothesis and also revealed the location of primary, secondary vents, flow tracts and all evolving volcanic landforms of the region and recorded the changes in flow directions. Further, for a comprehensive risk assessment of the region, volcanism, seismicity, and coastal dynamics along with crustal deformation need to be considered.

$\bf{Highlights}$

$\bullet$ The study has analyzed the eruption of Barren Island volcano and associated regional seismic activity from a Multi-Hazard perspective using satellite as well as field-based observations.

$\bullet$ These results provided stronger supportive evidences for coupling seismicity and volcanic eruptions at Barren Island volcano for the first time in this region and open up new vistas for research in this direction.

$\bullet$ The understanding of these two natural phenomena is very much needed for better preparedness with respect to disaster risk mitigation and management.