Probabilistic seismic hazard assessment at a strategic site in the Bay of Bengal

Trianni[1] S.C.T., Lai[2], C.G., Pasqualini[3], E.

Probabilistic seismic hazard assessment (PSHA) along the route of an offshore pipeline for the transport of oil in the Bay of Bengal has been performed. The complexity of geological and seismotectonic setting of the region where the pipeline is planned to be installed, is the result of the interaction of the Indian, Eurasian and Burmese tectonic plates. In order to properly account for the intricate way by which these plates interact, a large area extending 450 km from the pipeline route has been considered for the compilation of a comprehensive earthquake catalogue, spanning the period 1663 – 2012 AD.

Differently from earlier PSHA analyses conducted in the region based on assuming two-dimensional polygons as seismogenic provinces, this study adopted a seismotectonic source model which includes for the first time a linear tectonic lineament representing the northward extension of the Sunda mega thrust, responsible for the large Sumatra-Andaman earthquake of December 2004.

Hazard computations have been performed over a grid of sites spaced 0.045 degrees covering a rectangular area which contains the pipeline. Epistemic uncertainty in the hazard computations has been taken into account by a logic tree framework, incorporating different seismotectonic source models, maximum cut-off magnitude and ground-motion prediction equations.

Horizontal median uniform hazard spectra and median uniform hazard spectra plus and minus one sigma on stiff ground have been calculated at the selected sites for different return periods. Peak ground acceleration with 10% probability of exceedance in 50 years in correspondence of two land-terminal ends of the pipeline, at Chittagong, have been compared with values from previous hazard studies available for Bangladesh.

[1]PhD student, Dipartimento di Scienze e Ingegneria della Materia, dell'Ambiente ed Urbanistica, Università Politecnica delle Marche, Ancona, Italy

[2]Associate Professor, Dipartimento di Ingegneria Civile e Architettura, Università di Pavia, Italy

[3]Professor, Dipartimento di Scienze e Ingegneria della Materia, dell'Ambiente ed Urbanistica, Università Politecnica delle Marche, Ancona, Italy