Current Science

A. K. Rai ¹, S. Tripathy ¹, S. C. Sahu ²

Affiliations
1 School of Earth, Ocean and Climate Sciences, Indian Institute of Technology Bhubaneswar, Bhubaneswar 751 007, IN
2 India Meteorological Department, Bhubaneswar 751 020, IN

Abstract

The northeastern part of the Indian Ocean, i.e. the Bay of Bengal (BoB) is located near some of the most complicated tectonic zones on the Earth. An earthquake of magnitude ∼6.0 occurred on 21 May 2014 near the coast of Odisha. Occasional moderate to large earthquakes in BoB highlight the need to study precise hypocentre locations, and focal mechanisms to understand the cause of intraplate seismicity in BoB.It is also important for seismic hazard and tsunami risk evaluation along the eastern coast of India. We present an analysis of the digital data of this earthquake recorded by regional and global networks of seismic stations. Our analysis of travel-times of P- and S-waves indicates that the epicentre of the earthquake is located between the Eighty Five East and Ninety East ridges. The focus of this earthquake was at a depth of ∼61 km, well below the lower boundary of the oceanic crust. The focal mechanism determined by modelling long period P- and SH-waveforms suggest an strike-slip motion along a NW-SE or NEE-SWW-directed fault or fracture. We interpret that the upper part of the BoB lithosphere is abnormally strong and brittle.

Keywords

Earthquake Location, Focal Mechanism, Intraplate Seismicity, Tectonic Zones.

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S. C. Sahu ¹, Manish Kumar ², N. H. Ravindranath ¹

Affiliations
1 Centre for Sustainable Technologies, Indian Institute of Science, Bengaluru 560 012, IN
2 Environment and Sustainability Department, CSIR–Institute of Minerals and Materials Technology, Bhubaneswar 751 013, IN

Abstract

Mangrove forest ecosystem is one of the important carbon sinks in the tropics. The role of mangrove forests in mitigating climate change through reduced deforestation is well recognized. The present field study aimed to estimate the carbon stocks of Mahanadi Mangrove Wetland (MMW), east coast of India. Carbon stocks were estimated in vegetation and soil of natural mangrove forest stands and new mangrove plantation stands. The mean of carbon stock in natural stands was 143.4 ± 8.2 Mg C ha^-1 (vegetation 89.1 ± 8.9 and soil 54.3 ± 3.0 Mg C ha^-1) and plantation at 151.5 ± 7.9 Mg C ha^-1 (vegetation 90.6 ± 16.2 and soil 60.9 ± 5.6 Mg C ha^-1). The mean overall C-stock of natural stands and plantations was 147.0 ± 8.1 Mg C ha^-1 (vegetation 89.4 ± 7.6 and soil 57.6 ± 3.2 Mg C ha^-1), which is 1.6 times higher than that in forests of Odisha. A positive correlation (r = 0.87) was found between vegetation biomass and soil organic carbon in the surface soil (0-30 cm), indicating the role of vegetation in building surface soil/sediment organic carbon. The 6651 ha of mangrove forests in the MMW is estimated to store 0.98 Mt of C, which is equivalent to 3.59 Mt of CO₂e. The present study reveals that MMW stores substantial amount of atmospheric carbon and therefore needs to be conserved and sustainably managed to maintain as well as increase carbon storage. Further, mangrove plantations, on a per unit area basis, can sequester as much carbon as natural stands.

Keywords

Carbon Stocks, Mangroves, Natural Stands, Plantations.

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