A Three-Dimensional Regional-Scale Earthquake Ground Motion Simulation for the Bengal Basin

Abstract eng:
This study presents the initial results of a project with the goal of studying the ground motion characteristics of the Bengal basin region in Bangladesh, south Asia, through the simulation of a series of historical, recorded and scenario earthquakes. Bangladesh is one of the most densely populated countries in the world, with more than one thousand people per square kilometer, and several cities exceeding a few millions habitants. Most people in Bangladesh live in poorly constructed (often unreinforced) buildings. The country land is shaped by the Ganges delta, the largest delta system in the world, which rests over a sedimentary structure with thicknesses that can reach up to 20 km. The lithospheric structure is dominated by the different orogeny systems created by the collision between the Indian, Eurasian and Burmese tectonic plates. Depending on the geological setting, Bangladesh can be divided into three provinces: the stable shelf, which is part of the Indian continental plate at the northwest; the central deep basin, covering most of Bangladesh; and the Chittagong-Tripura fold belt at the eastern border, created by the oblique subduction of the oceanic crust under the Burmese plate. The region is bounded by the Dauki fault to the north and north-east, the Bogra fault on the stable shelf region, boundary thrust faults at Chittagong-Tripura fold belt region to the east, and the Madhupur fault and some other ambiguous faults inside the basin. These systems place Bangladesh under high seismic hazard, and given the population density and infrastructure conditions it is assumed the country presents elevated levels of seismic risk. This situation is worsen by the tremendous scarcity of seismic data, despite the significant seismic activity in the region. Under these conditions, simulations can provide valuable input to better understand the potential effects of a major earthquake affecting the Bengal basin. However, in order to perform ground motion simulations, the first step is to construct a reliable seismic velocity model for the region. Here, we present the initial version of a three-dimensional model built upon a geology-based representation of the geometry of the Bengal basin and simple approximations of the basin deposits, crustal, and background structures. We show results for a low-frequency ground motion simulation ( f ≤ 0.5 Hz) of the 10 September 2010 Mw 5.1 Chandpur earthquake and compare basic qualitative characteristics observed in the synthetics with a limited number of records available. The simulations are done using a finite-element parallel code. Using these initial results we investigate the influence of basic features such as fault boundaries and basin depth, and shed light over future steps necessary to better characterize earthquake ground motions in the region.

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