Site-specific seismic hazard and risk potential of Bengal Basin with emphasis on holistic seismic hazard microzonation and its structural impact assessment in the cities of Dhanbad and Mymensingh

Abstract

The Bengal Basin located in the eastern part of the Indian subcontinent at the conjunction of the Eurasian, Indian, and Indo-Burma plates with two progressing deformation fronts viz. the Himalayas and the Indo-Burmese orogenic belts is one of the largest fluvio-deltaic to shallow marine sedimentary basin covered by alluvial plains of Holocene deposits extending from the Himalayas to the Bay of Bengal over thick younger alluvium comprising shallow layers of silt, clay, and sand that can have disastrous consequences due to site-specific ground motion amplification and liquefaction effects. The basin surrounded by Shillong and Assam plateaus in the Northeast is in the active tectonofabric of major active faults and lineaments triggering many devastating earthquakes in the past implicating the MM Intensity of VIII–XI in the near-source region causing widespread damage and destruction in the basin, thus bringing in the essence of assessing surface level seismic hazard and the risk imposed on the basin. Consideration of seismicity patterns, fault networks, and similarity in focal mechanisms yielded 49 areal seismogenic sources and additional active tectonic features in the 0–25 km, 25–70 km, and 70–180 km hypocentral depth ranges, which along with 14 ground motion prediction equations that include site-specific next generation spectral attenuation models pertaining to Northeast India, East-Central Himalaya, and Bengal Basin tectonic provinces yielded probabilistic peak ground acceleration (PGA) at engineering bedrock in the range of 0.08–0.58 g. Both the geophysical and geotechnical investigations at 6,000 sites provided effective shear wave velocity distribution in the range of 113–948 m/s on the geographical information system, thus classifying the basin into 11 site classes with “None” to “Severe” liquefaction hazard potential. A systematic non-linear/equivalent linear site response analysis and its spectral convolution with firm rock peak ground acceleration yielded surface-consistent hazard in the range of 0.09–1.17 g, thus opening up the issue of risk assessment and holistic seismic hazard microzonation of all the cities in the basin and their structural impact assessment using the SELENA-based capacity spectrum method on FEMA and BMTPC-regulated 11 model building types in the damage states of “none,” “slight,” “moderate,” “extensive,” and “complete” for all of those, however, in-depth studies carried out for Mymensingh and Dhanbad have been presented.

Cascading hazards of a major Bengal basin earthquake and abrupt avulsion of the Ganges River

“…Moreover, urbanization, industrialization, and population pressure extend the potential damages of flooding, liquefaction, and avulsion to lowland cities and agricultural plains 81,90,91 . In sedimentary basins such as the Bengal and others draining the Himalayan arc, growing urban centers and industrial development are commonly constructed on saturated, under-consolidated Holocene sands susceptible to liquefaction [92][93][94] . This is acutely illustrated by dredge-fill construction sites around Dhaka (Fig.…”

Site-characterization using 1D/2D/3D Site Response Modelling vis-à-vis Surface-consistent Probabilistic Seismic Hazard, Microzonation and Damage Potential Studies in the Six-Tectonic Ensemble consisting of Kashmir Himalaya to Northeast India

“…The seismic loading causes a sudden increase in pore water pressure and the gaps between soil grains, leading the soil to loosen its cohesive strength and behave like a liquid. The Brahmaputra Valley of Northeast India, Indo-Gangetic Foredeep, Bengal Basin and Northwest India are particularly susceptible to liquefaction, as documented in the regions such as Jammu (Ansari et al 2022), Kashmir Valley (Sana and Nath 2016), Lucknow (Kumar et al 2013), Delhi (Rao and Satyam 2007), Kathmandu (Subedi and Acharya 2022;Pokhrel et al 2022), Bengal Basin including Bangladesh (Nath et al 2022), Guwahati (Raghukanth and Das 2010), Agartala (Das et al 2019) and Imphal (Pallav et al 2012). A comprehensive analysis of soil liquefaction has been conducted for the present Tectonic Ensemble, utilizing geotechnical data to simulate liquefaction susceptibility due to historical earthquakes and predict probabilistic scenarios for the Basin.…”

“…In the field of Multi-criteria Seismic Hazard Microzonation, an integration technique based on Saaty's (1980) Analytic Hierarchy Process (AHP) is used. This method has previously been employed in Dhanbad (Nath et al 2022), Kachchh (Pancholi et al 2022), Kolkata (Nath et al 2014), Chennai (Ganapathy 2011), Guwahati (Nath et al 2007) and the Sikkim Himalaya (Nath 2004). In the present study, the focus is on the AHP hierarchical structure, which quantifies the relative importance of thematic layers based on user judgment.…”