The research, led by Arpita Biswas of the Indian Institute of Technology Kharagpur together with Sankar Kumar Nath of the University of Burdwan, drew on an extraordinary geotechnical and geophysical database of approximately 6,000 investigation sites across the basin. These included Standard Penetration Test boreholes, downhole seismic surveys, multichannel analysis of surface waves, ambient noise measurements and resistivity surveys, supplemented by laboratory tests on soil samples for grain size, moisture content, plasticity and density. The sheer scale of the dataset allowed the team to move beyond the city-level case studies — focused previously on Kolkata, Dhaka and Chittagong — that had dominated liquefaction research in the region.

The geological setting could hardly be more favourable for liquefaction. The basin contains the world’s deepest Neogene-to-recent sedimentary accumulation, exceeding 18 kilometres in thickness, and about 77 percent of the study area is blanketed in Quaternary alluvium — loose silt, sand, clay and gravel deposited by the Ganges, Brahmaputra and Meghna rivers. Statistical analysis of the borehole data revealed that the upper 15 metres of basin sediment is very loose to medium dense, with corrected penetration values averaging between 6 and 35 depending on depth, and a mean fines content of just 36.8 percent, indicating predominantly coarse-grained soils. Grain-size curves for sites in Dhaka, Rajshahi, Kalyani and Bhubaneswar showed that most soil layers fall within the internationally recognised boundaries of ‘most liquefiable’ and ‘potentially liquefiable’ soils.

Groundwater compounds the danger. Post-monsoon water tables across the basin range from just 0.27 to 4.71 metres below the surface, and shallow groundwater dramatically lowers the effective confining stress on sediments, creating ideal conditions for pore-pressure buildup during shaking. Historical precedent is sobering: the 1885 Bengal earthquake of magnitude 6.8, the 1897 Shillong earthquake of magnitude 8.1, the 1918 Srimangal earthquake of magnitude 7.6 and the 1934 Bihar-Nepal earthquake of magnitude 8.1 all triggered documented liquefaction, leaving ground fissures, sand boils, lateral spreading and soil slumping in their wake. Even moderate events such as the 2003 Kolabunia earthquake of magnitude 5.6 produced ground rupture along riverbanks in Rangamati.

Methodologically, the study is a tour de force of integrated hazard modelling. Because instrumental recordings are absent for the great historical earthquakes, the team used the EXSIM finite-fault stochastic simulation technique, which discretises a fault plane into numerous subsources and sums their contributions with realistic rupture propagation and travel-time delays. The resulting bedrock motions were then fed into two-dimensional nonlinear finite element site response analyses in PLAXIS 2D, capturing soil behaviour that simpler one-dimensional equivalent-linear methods miss. The simulated ground motions were validated against Modified Mercalli intensities derived from historical isoseismal maps, yielding a root-mean-square error of 0.91 — a respectable agreement for regional-scale work.

The probabilistic component is equally ambitious. Combining a comprehensive probabilistic seismic hazard model with fourteen ground-motion prediction equations, the researchers computed bedrock peak ground acceleration for a 475-year return period — the conventional design-basis earthquake — ranging from 0.08 to 0.58 g. Multiplying these values by spatially interpolated site amplification factors, which ranged from 1.30 to as much as 4.60 in the soft coastal deposits of the Sundarbans, produced surface-consistent hazard values reaching a remarkable 1.40 g near Sylhet in the northeast, close to the Dauki fault and the Indo-Burman subduction zone. Cities such as Mymensingh and Sylhet fell into the ‘severe’ category, while Dhaka, Kolkata and Khulna were rated ‘moderate’ and Bhubaneswar and Dhanbad ‘low’.

With these ground motions in hand, the team evaluated liquefaction using the stress-based framework of Idriss and Boulanger, computing factors of safety for every soil layer, then aggregating them into the Liquefaction Potential Index, the Liquefaction Risk Index, the probability of liquefaction and the probability of ground failure. The results are stark: under the probabilistic scenario, roughly 42 percent of the basin’s area falls into the ‘severe’ liquefaction potential class, with a further 35 percent rated ‘high’. Dhaka, Sylhet, Mymensingh, Chittagong, Barisal, Khulna and Rangpur all exceed the severe threshold of LPI greater than 15, while Rajshahi and Kolkata sit in the high class. The risk index map places nearly half the region — about 48 percent — in the ‘extremely high’ risk zone. At representative sites including Dhaka, Chittagong, Haldia and Kalna, probabilities of liquefaction exceeded 65 percent between depths of 5 and 20 metres, and cities from Dhaka to Barasat showed probabilities of ground failure above 0.9 — ‘extremely high to absolutely certain’.

Crucially, the modelled hazard aligns with reality. The predicted severity zones show an increasing trend in the number of documented liquefaction occurrences, providing qualitative validation of the approach. The spatial pattern also makes geological sense: the northeast around Sylhet and Mymensingh combines high seismic loading from nearby active faults with young floodplain deposits and shallow groundwater, while the southwest, underlain by older, stiffer sediments near the Indian Shield, fares considerably better. Notably, the study shows that strong shaking alone does not guarantee severe liquefaction — the Chittagong Fold Belt’s uplifted, folded sediments partially offset high seismic demand, whereas the unconsolidated Holocene deltaic plains of Khulna and Barisal remain highly susceptible despite more moderate loading.

Perhaps the most practically valuable contribution is the back-analysis of target penetration resistance. By reversing the standard liquefaction triggering equations, the researchers calculated the improved SPT-N values — denoted N-improved — needed at each site to guarantee no liquefaction under the probabilistic scenario, assuming a target factor of safety of 1.5. Mapped at depth intervals from 5 to 20 metres, these values range from as low as 1 in the stable west to 50 at 20-metre depth in the most demanding northeastern locations. Such maps give engineers, contractors and planners a first-order estimate of the densification or reinforcement required at specific sites, bridging the persistent gap between regional hazard assessment and ground-level engineering decisions.

The authors are candid about limitations: the empirical triggering relationships were calibrated on global case histories rather than Bengal Basin-specific data, uncertainties were not formally propagated through the entire framework, and the maps represent regional trends rather than site-specific design criteria. Ground improvement techniques — vibro-compaction, stone columns, gravel drains, grouting, dewatering and reinforcement — each have their place depending on geology, land use and economics, and the study suggests densification suits the young deltaic south while targeted foundation measures may be more realistic in congested megacities like Dhaka. Still, as a unified, basin-scale portrait of liquefaction threat across one of the world’s most populous regions, the work offers an essential foundation for risk-informed urban planning — and a sobering reminder that beneath the streets of Dhaka and the fields of Sylhet, the ground itself may be the region’s most insidious seismic hazard.

Subject of Research: Assessment of earthquake-induced soil liquefaction potential and mitigation targets across the Bengal Basin using probabilistic seismic hazard analysis and historical earthquake scenarios

Article Title: Probabilistic seismic hazard and historical scenario-based assessment of liquefaction potential in the Bengal Basin for liquefaction mitigation strategies

Article References: Biswas, A., & Nath, S. K. (2026). Probabilistic seismic hazard and historical scenario-based assessment of liquefaction potential in the Bengal Basin for liquefaction mitigation strategies. Discover Geoscience, 4(1), Article 293. https://doi.org/10.1007/s44288-026-00672-6

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00672-6

Keywords: Bengal Basin, soil liquefaction, seismic hazard, liquefaction potential index, probabilistic seismic hazard analysis, ground motion simulation, site amplification, Standard Penetration Test, ground improvement, earthquake engineering, Ganges-Brahmaputra delta, geotechnical investigation

The research, led by laila TAOUFIQ of Ibn Zohr University and Universiapolis in Agadir, together with Mehdi Harrak, Mimoun Chourak, and Fatima Ezzahra Arrakhiz, set out to identify the root causes of structural failure rather than simply cataloguing the destruction. Earthen buildings constitute a substantial portion of the rural housing stock in the affected High Atlas region, and their vulnerability has long been recognized by earthquake engineers. Morocco does have a seismic regulation specifically for earthen constructions, known as RPCT11, adopted by decree in 2013, but the study’s findings suggest that both the regulation and everyday building practice fell short of what the Al Haouz earthquake demanded. The team frames its work as a direct contribution to seismic risk reduction strategy and to the revision and update of RPCT11 itself.

Field observations revealed a consistent pattern of damage across the affected villages. The most common failures included cracks and outright collapse of masonry walls, the fall of roofs and floors, out-of-plane failure in which walls toppled bodily outward or inward perpendicular to their surface, and failures originating at the foundation level. Each of these modes tells a mechanical story. Unreinforced earthen walls are strong in compression but weak in tension and shear, so when ground shaking imposes lateral forces, the walls crack along diagonal planes or separate at corners. Once the box-like integrity of the building is lost, walls acting as independent vertical cantilevers have little resistance left, and out-of-plane collapse follows, often bringing heavy timber-and-earth roofs down with them.

The authors attribute the observed damage to a combination of factors rather than a single cause. Structural deficiencies ranked high: many buildings lacked the wall-to-wall and wall-to-roof connections that allow a structure to behave as a unified three-dimensional frame during shaking. Material limitations compounded the problem, since unfired earth has inherently modest strength, and moisture content, clay mineralogy, and compaction quality all influence how much load an earthen wall can carry. Weak connections between roofing systems and supporting walls meant that roofs could detach and fall as rigid masses, a particularly lethal failure mode. Finally, unfavorable topographical and geotechnical conditions amplified ground motion in some locations, placing certain buildings on ground that shook harder and longer than adjacent sites.

To understand these site effects and soil-structure interactions, the team investigated geotechnical parameters in the most severely affected areas. Such investigations typically involve characterizing the soils on which buildings rest, including particle size distribution, plasticity limits determined through Atterberg tests, and compaction characteristics measured by Proctor testing, all of which appear in the study’s reference framework of Moroccan and international standards. Soft or loose soils can amplify seismic waves and lengthen the duration of strong shaking, while steep mountain slopes in the High Atlas can concentrate motion near ridge crests. When vulnerable earthen structures sit on amplifying ground, the demand placed on already weak walls can exceed their capacity by a wide margin, which helps explain the localized severity of collapse observed in some villages.

The earthquake itself was an unusual and sobering event for Moroccan seismology. Scientific work cited by the study describes the rupture as intraplate reverse faulting within the High Atlas mountain belt, with a deep transpressive fault accommodating the shortening of the African plate’s interior. The event, sometimes referred to as the Adassil earthquake, occurred on a steep reverse fault in the deep crust, and rapid source characterization confirmed its magnitude at 6.8. Morocco’s earthquake catalog, which extends back more than a millennium, records destructive events in the region, but the 2023 earthquake struck a mountainous rural zone where building vulnerability, rather than ground motion alone, controlled the death toll.

What distinguishes the new study is its constructive response to the failure evidence. Based on their findings, the researchers propose a guideline for the construction of buildings made of adobe, rammed earth, and stone, the three dominant earthen and semi-earthen technologies of the region. Adobe involves sun-dried mud bricks laid in mud mortar, rammed earth consists of moist soil compacted in layers within formwork, and stone masonry uses locally quarried rock, often with weak mud mortar in rural practice. The recommendations aim to enhance the seismic resilience of all three building types and to improve protection for both people and their cultural heritage, a dual goal that reflects the region’s extraordinary legacy of earthen architecture, from kasbahs to vernacular village houses.

The engineering logic behind such guidelines draws on a broad international literature that the study situates itself within. Research following earthquakes in Nepal, Turkey, Peru, Italy, and Greece has repeatedly shown that simple, low-cost measures can transform the survival prospects of unreinforced masonry and earthen buildings. Horizontal seismic bands or ring beams at wall tops and floor levels tie the structure together and prevent walls from separating; corner and junction reinforcement resists cracking at the weakest points; and roof lightening reduces the inertial forces and the deadly falling mass. Experimental work on adobe walls strengthened with timber ring beams, on rammed earth reinforced with natural fibers such as coir and bamboo, and on stone masonry retrofitted with reinforced mortar coatings all point toward interventions that remain affordable and culturally acceptable in rural communities.

Material science offers another layer of improvement. Studies of stabilized earth blocks show that small additions of cement or lime can raise strength and durability, though researchers caution that excessive stabilization undermines the environmental advantages that make earthen construction attractive in the first place. Rammed earth’s mechanical behavior is sensitive to moisture content and compaction energy, and modern testing standards now allow engineers to characterize earthen materials with the same rigor applied to conventional construction materials. The Moroccan context is particularly well studied: earlier characterization of soils from the Haouz plain and from oases in southeastern Morocco has documented the suitability of local earth for construction, provided that grading, plasticity, and stabilization are controlled. The new guidelines translate this accumulated knowledge into rules that builders on the ground can actually follow.

The stakes extend beyond Morocco. Earthen construction houses a substantial fraction of the world’s rural population, and as climate change intensifies interest in low-carbon building materials, earth is enjoying renewed attention as a sustainable alternative to fired brick and concrete. The Al Haouz earthquake demonstrated in the starkest terms that sustainability and safety must advance together: a building material with excellent embodied-energy credentials is of little value if it collapses in a moderate earthquake. By documenting failure mechanisms systematically and feeding the results into the revision of RPCT11, the Moroccan team offers a template for other earthquake-prone countries with rich earthen building traditions. The goal, as the authors put it, is to enhance seismic resilience and improve protection for both people and their cultural heritage, ensuring that the architecture of the High Atlas can continue to house generations without becoming their grave.

Subject of Research: Seismic failure mechanisms and resilience improvement of earthen buildings after the 2023 Al Haouz earthquake in Morocco

Article Title: Analysis of failure mechanisms in earthen buildings after the 2023 Al Haouz earthquake in Morocco and improvement solutions

Article References: TAOUFIQ, L., Harrak, M., Chourak, M., & Arrakhiz, F. E. (2026). Analysis of failure mechanisms in earthen buildings after the 2023 Al Haouz earthquake in Morocco and improvement solutions. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02693-5

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02693-5

Keywords: Al Haouz earthquake, Morocco, earthen buildings, adobe, rammed earth, stone masonry, seismic vulnerability, out-of-plane failure, geotechnical investigation, RPCT11, High Atlas, cultural heritage