Towards Improved Probabilistic Seismic Hazard Assessment for Bangladesh

This study aims to build on the existing knowledge and improve the overall PSHA results by modifying source, path and site characteristics for Bangladesh. Firstly, six potential seismotectonic zones have been re-defined based on the recent study of Wang et al. (J Geophys Res Solid Earth 119:3576-3822, 2014) and Nath and Thingbaijam (J Seismol 15(2):295-315, 2011), and the updated earthquake catalogue has been declustered using two methods. Important source parameters, such as recurrence b-values and maximum magnitudes, have been determined using the Maximum Likelihood and cumulative moment methods, respectively, and their uncertainties have been addressed using a logic-tree approach. Secondly, based on literature review and studies in neighboring countries, suitable GMPEs have been selected for the seismic zones and the uncertainties have been addressed using a logic tree approach. A significant novelty of the study lies in the consideration of the site effects by integrating Vs30 values throughout the country. The ground motions-PGA and SA (at 0.2, 1.0 and 2.0 s) are computed using GEM's OpenQuake and presented in form of hazard maps for 2% and 10% probabilities of exceedance in 50 years as well as mean hazard curves and uniform hazard spectra. Disaggregation for capital city Dhaka has also been carried out to show the hazard contributions of magnitude-distance pairs. The spatial distribution of PGA and SA are found remarkably higher than previous findings, likely due to differences in parameters and uncertainties. The results show a marked increase (by almost 20%) in the observed ground motions with respect to those carried out previously by uniformly characterizing the whole country as a firm rock.