Intensity Attenuation Model Evaluation for Bangladesh with Respect to the Surrounding Potential Seismotectonic Regimes

An effort has been made through this study to evaluate the existing intensity attenuation model (IPE) for the potential seismotectonic regimes in and around Bangladesh. To reach the goal, the seismicity of the concerned tectonic regimes has been analyzed. Apart from evaluating the appropriate intensity model, this research has also assessed the predictive performance of epicentral intensity estimation. Different magnitude types have been made uniform by converting into moment magnitude and subsequently into the Modified Mercalli Intensity scale (MMI). The epicentral intensity conversion following Li in Chinese Earthquakes (Seismological Press, Beijing, 1980) fits best for the study area among the utilized four predictive equations. The epicentral intensity conversion from the moment magnitude shows that small to moderate earthquakes get significantly overestimated. Suitable attenuation models have been applied to the different tectonic regimes based on the criteria of using the IPEs. Among all the utilized IPEs, the relation of Bakun et al. (Bull Seismol Soc Am 93:190-202, 2003) exhibits the highest standard deviation (sigma = 1.61) in attenuation with distance. Although the Szeliga et al.'s (Bull Seismol Soc Am 100(2):570-584, 2010) attenuation relation has a standard deviation of 1.22, the intensity decay is little even for the greater distance (~ 800-900 km). Up to M-w 7.0, the IPE of Bindi et al. (Geophys J Int 187(1):327-337, 2011) shows realistic attenuation scenario (with sigma = 1.3); however, at lower magnitude range (< M-w 7.0), the intensity starts to decay sharply. Still, the IPE of Bindi et al. (2011) is more realistic in comparison of the shakemaps of the past and in terms of convincible intensity decay with greater distance (~ 500-900 km). However, the intensity close to the epicenter gets very high MMI (XI or larger) value for the major events (M-w >= 8.5). Although the IPE of Chandler and Lam (J Asian Earth Sci 20(7):775-790, 2002) has distance constraints, its performance is acceptable considering the attenuation scenario with distance along with the lowest standard deviation (~ 0.92). Considering the seismic events from the only strike-slip Churachandpur Mao fault of the study area, Bakun and Wentworth (Bull Seismol Soc Am 87(6):1502-1521, 1997) relation has been applied to determine the attenuation pattern.