Bihar-Nepal Earthquake Research Articles

Revisiting the 1934 Mw 8.2 Bihar–Nepal earthquake—Simulation of broadband ground motions

SUMMARY The 1934 Mw 8.2 Bihar–Nepal earthquake was one of the devastating earthquakes, which made seismologists realize the importance of proper seismic hazard analysis and design aspects in India. The event occurred way before proper seismic networks were implemented and hence there are no recorded ground motions available for this event. This study, thus aims to generate possible ground motions for the 1934 Mw 8.2 Bihar–Nepal event. The complex geographical features, ambiguous source information and lack of ground motion data make the simulation and validation of ground motions very difficult. In this regard, the broad-band (BB) ground motions are simulated and validated for the most recent well-documented Himalayan event, that is, the 2015 Mw 7.9 Nepal earthquake in order to calibrate the model and simulation methodology. For this purpose, the computational model is presented for a region of 1000 km × 670 km (longitude 80–89 °E and latitude 23–30 °N) in the Indo-Gangetic Basin to simulate the low-frequency (LF) ground motions using spectral element method. These deterministically simulated LF ground motions are combined with stochastically simulated high-frequency (HF) ground motions based on an improved seismological model . The seismic moment and dimensions of the rupture plane are used to generate ten samples for the finite fault source model having different slip distribution along the rupture plane as a random field. The BB ground motions (0.01–25 Hz) are obtained by merging LF and HF ground motions in the time domain by matching them at a frequency of ∼0.3 Hz. Such BB results are simulated at a grid of stations and at locations where modified Mercalli intensity (MMI) values are available. The estimated MMI values and the observed MMI values are compared to emphasize the efficacy of the model. The maximum PGA estimated from the simulated ground motions in horizontal and vertical directions are observed to be 0.48 g and 0.4 g. Further, 5 per cent damped response spectra and spectral amplification are analysed concerning the sediment depth of the Indo-Gangetic Basin. The results from the study can serve as inputs for dynamic analysis and the design of earthquake-resistant structures across different locations in the Indo-Gangetic Basin.

Probabilistic Seismic Hazard Assessment of Sitamarhi near the Central Himalayan Region

ABSTRACT Sitamarhi, situated in the North-Bihar region of the Himalayan foothills is one of the seismically vulnerable regions of India. This region faced several devastating earthquakes, such as the 1934 and 1988 Bihar Nepal earthquake and the 2015 Nepal earthquake due to the movement of tectonic plates. The purpose of the present study is to exhibit the uniform hazard spectrum (UHS) and peak ground acceleration (PGA) values based on the probabilistic seismic hazard method using different seismotectonic parameters. The Gutenberg Richter (G-R) seismicity parameters ‘a’ and ‘b’ were estimated on the basis of regional earthquake magnitude data for the studied region. Regional earthquakes data were taken from the United States Geological Survey (USGS), International Seismological Centre (ISC), Indian Meteorological Department (IMD), and Seismotectonic Atlas of India. The region of interest for the probabilistic seismic hazard analysis (PSHA) is within a 500 km radius considering past seismicity and 62 seismotectonic sources which were identified in the study area. Large-scale geological features were utilised to describe the regional seismic source zones, which were used to derive the relationship between return period and ground motion parameters. Estimated PGA values are 0.92g for 2% and 0.68g for 10% probability of exceedance in 50 years time period, respectively. This research infer that the West Patna fault (WPF) and Sitamarhi fault (SMF) are the two maximum contributors in PGA for the Sitamarhi region.

Representations of disaster victimhood: Framing suffering and loss after the 1934 Bihar-Nepal earthquake

AbstractThis article seeks to address a thematic thread that remains relatively unexplored in historical disaster research—victimhood—through an analysis of publications by disaster relief funds and their supporters in the aftermath of the 1934 earthquake in Bihar in northern India. By examining the representations of victimhood, I aim to explore the historical significance of perceptions and constructions of victimhood in the late colonial period. Based on photographs, illustrations, and descriptions of suffering in images and texts, the article suggests that constructions of victimhood effectively relied on imagery that contained, on the one hand, an absence of bodies and, on the other, a feminized anthropomorphization of suffering. The narratives underlying such depictions of earthquake victims are based on a constitution of victimhood that relied on contemporary historical and culturally founded imageries. The analysis of images and texts focuses on how representations of disaster victims were effective in communicating suffering to audiences. I tentatively argue that historically and culturally founded tropes of what constituted a victim formed along two narratives of victimhood that appealed to a colonial and a nationalist readership respectively. These conceptualizations of victimhood formed the basis for collecting aid for relief and reconstruction, rather than the loss of life, dispossession, social marginalization, and displacement suffered by victims of the earthquake.

Seismic hazard assessment of the Kathmandu Valley and its adjoining region using a segment of the main Himalayan Thrust as a source

An attempt has been made to evaluate seismic hazard in the Kathmandu Valley and its adjoining region. A segment of the Main Himalayan Thrust, which produced the 2015 Gorkha Earthquake is used as an earthquake source. Two rupture models of the source are utilized assigning unequal weight to estimate seismic hazard. The first model considers entire north-south rupture of the source that is similar to the rupture of the 1934 Bihar-Nepal Earthquake (Mw 8.2). The second model considers the northern-half rupture of the source, which is similar to that of the 2015 Gorkha Earthquake (Mw 7.8) and possibly the 1833 Nepal Earthquake (Mw 7.6).Seismic hazard maps are prepared for 500 and 200 year return periods at engineering rock site condition. A comparison is made between the peak ground acceleration (PGA) of Kathmandu and Nijgadh estimated for 200 year return period with the recorded PGA of the 2015 Gorkha Earthquake in Kathmandu (Kirtipur: a rock site) and empirically estimated PGA of that earthquake in Nijgadh respectively. Kathmandu and Nijgadh are selected for the comparison because Kathmandu falls within the rupture area of the 2015 Gorkha Earthquake and Nijgadh is in the Indogangetic Plain and away from the rupture area of that earthquake. The result shows that the PGA (0.23 g) estimated for Kathmandu for 200 year return period closely agrees with the instrumentally recorded PGA of the 2015 Gorkha Earthquake in Kathmandu (0.25 g). Instrumentally recorded PGA is not available in Nijgadh, which is at about 55 km in the south from Kathmandu. A seismic intensity survey was carried out in Nijgadh and its adjoining region to estimate the intensity of the 2015 Gorkha Earthquake in Nijgadh. The probabilistically estimated PGA (0.1 g) for Nijgadh for 200 year return period is in reasonable agreement with that of the 2015 Gorkha Earthquake (0.07 g) estimated from the seismic intensity (VI on MMI).

Large Himalayan Frontal Thrust paleoearthquake at Khayarmara in eastern Nepal

An exposure created by excavation of a trench across the Himalayan Frontal Thrust provides the basis to interpret that a single earthquake produced vertical separation of ∼7 m at Khayarmara, a small community ∼80 km southwest of Kathmandu. The fault trace at Khayarmara is expresssed by a topographic ridge resulting from folding up-dip and toward the surface at the expense of greater fault slip taking place at depth. Structure, stratigraphy, and radiocarbon data are interpreted to indicate displacement occurred after about 1050 CE to 1200 CE. The timing and displacement at Khayarmara are compared to that reported previously at six contiguous sites that extend from 200 km to the west and 250 km to the east of Khayarmara, respectively. The comparison leads us to conclude that the surface rupture at Khayarmara was part of a ≥250 km long synchronous surface rupture earthquake of magnitude approaching if not surpassing Mw 9. We observe in the exposure no record of surface rupture associated with the great 1934 Bihar-Nepal earthquake.

Derive empirical fragility functions for Nepali residential buildings

Fragility functions are the key components of damage analysis for the next generation performance-based earthquake engineering (PBEE-2) framework. Despite being widely discussed and researched topic in almost all seismically active regions, fragility functions for Nepali buildings are not widely researched to date. This paper derives empirical fragility functions for residential buildings using more than a million damage data from the 1934 Bihar-Nepal earthquake (MW ∼8.4), 1980 Chainpur earthquake (MW 6.5), 1988 Eastern Nepal earthquake (MW 6.8), 2011 Eastern Nepal earthquake (MW 6.9), and 2015 Gorkha seismic sequence (MW 7.8). A new damage classification system is proposed in this study and fragility functions for reinforced concrete, brick masonry, and stone masonry building classes are derived. As seismic site effects is one of the leading factor contributing damage in the case of Himalayan earthquakes, fragility functions considering seismic site effects are also derived for all three building classes. Finally, fragility functions derived in this study are compared with existing fragility functions and discussion regarding the discrepancies is presented. Together with the fragility functions, building taxonomy and vulnerability of all existing buildings in Nepal are outlined in this paper.

Earthquake induced liquefaction hazard, probability and risk assessment in the city of Kolkata, India: its historical perspective and deterministic scenario

Liquefaction-induced ground failure is one amongst the leading causes of infrastructure damage due to the impact of large earthquakes in unconsolidated, non-cohesive, water saturated alluvial terrains. The city of Kolkata is located on the potentially liquefiable alluvial fan deposits of Ganga-Bramhaputra-Meghna Delta system with subsurface litho-stratigraphic sequence comprising of varying percentages of clay, cohesionless silt, sand, and gravel interbedded with decomposed wood and peat. Additionally, the region has moderately shallow groundwater condition especially in the post-monsoon seasons. In view of burgeoning population, there had been unplanned expansion of settlements in the hazardous geological, geomorphological, and hydrological conditions exposing the city to severe liquefaction hazard. The 1897 Shillong and 1934 Bihar-Nepal earthquakes both of M w 8.1 reportedly induced Modified Mercalli Intensity of IV–V and VI–VII respectively in the city reportedly triggering widespread to sporadic liquefaction condition with surface manifestation of sand boils, lateral spreading, ground subsidence, etc., thus posing a strong case for liquefaction potential analysis in the terrain. With the motivation of assessing seismic hazard, vulnerability, and risk of the city of Kolkata through a consorted federal funding stipulated for all the metros and upstart urban centers in India located in BIS seismic zones III, IV, and V with population more than one million, an attempt has been made here to understand the liquefaction susceptibility condition of Kolkata under the impact of earthquake loading employing modern multivariate techniques and also to predict deterministic liquefaction scenario of the city in the event of a probabilistic seismic hazard condition with 10% probability of exceedance in 50 years and a return period of 475 years. We conducted in-depth geophysical and geotechnical investigations in the city encompassing 435 km2 area. The stochastically synthesized bedrock ground motion for both the 1897 and 1934 earthquakes on non-linear analysis of local site conditions through DEEPSOIL Geotechnical analysis package present surface level peak ground acceleration of the order of 0.05–0.14 g for the 1934 Bihar-Nepal earthquake while for the 1897 Shillong earthquake it is found to be in the range of 0.03–0.11 g. The factor of safety (FOS) against liquefaction, the probability of liquefaction (P L), the liquefaction potential index (LPI), and the liquefaction risk index are estimated under the influence of these two earthquakes wherein the city is classified into severe (LPI > 15), high (5 < LPI ≤ 15), moderate (0 < LPI ≤ 5), and non-liquefiable (LPI = 0) susceptibility zones. While the 1934 Bihar-Nepal earthquake induced moderate to severe liquefaction hazard condition in the city in mostly the deltaic plain and interdistributary marsh geomorphologic units with 13.5% sites exhibiting moderate hazard with a median LPI of 1.8, 8.5% sites depicting high with a median LPI of 9.1 and 4% sites with a median LPI of 18.9 exhibiting severe hazard condition, 1897 Shillong earthquake induced mostly non-liquefaction condition with very few sites depicting moderate and high liquefaction hazard. A conservative liquefaction hazard scenario of the city on the other hand estimated through deterministic approach for 10% probability of exceedance in 50 years predicts a high hazard zone in the 3.5–19 m depth region with FOS < 1 and P L > 65% comprising of coarse-grained sediments of sand, silty sand, and clayey silty sand in mostly the deltaic plain geomorphologic unit with 39.1% sites depicting severe liquefaction hazard with a median LPI of 28.3. A non-linear regression analysis on both the historical and deterministic liquefaction scenarios in P L versus LPI domain with ± 1 standard deviation confidence bound generated a cubic polynomial relationship between the two liquefaction hazard proxies. This study considered a bench mark for other cities in the country and elsewhere forms an integral part of the mega-seismic microzonation endeavors undertaken in all the earthquake-prone counties in the world.

Relevance of seismicity in Kumaun-Garhwal Himalaya in context of recent 25th April 2015 Mw7.8 Nepal earthquake

Due to the continuous movement of underthrusting Indian plate beneath the Eurasian plate the strain energy accumulates, which is released substantially in the form of great earthquakes. It is yet to be released in the unruptured zone which lies between the two great earthquakes viz. 1934 Bihar-Nepal earthquake and 1905 Kangra earthquake. This zone has been termed as the Central Seismic Gap (CSG). The occurrence of previous great earthquakes and recent Nepal earthquakes, gives a clue to the probable location of future great earthquake. On the basis of analysis of seismicity in the locked portion and the stress drop analysis the CSG has been redefined and location of probable zone of future great earthquake has been demarcated.

Structural performance and associated lessons to be learned from world earthquakes in Nepal after 25 April 2015 (MW 7.8) Gorkha earthquake

Abstract Gorkha earthquake (MW 7.8) occurred in Nepal on 25 April 2015 at 11:56 local time. This earthquake is the most devastating event after the 1934 great Bihar-Nepal earthquake (MW 8.1) in terms of damages. In that earthquake, 498,852 buildings were completely collapsed and other 256,697 were partially damaged. Structural and non-structural damages were occurred in all types of prevalent structural systems in affected areas. This paper outlines the structural performance during Turkey, Bhuj, Kashmir, Haiti, Chile and L'Aquila earthquakes from past two decades worldwide and comparisons are made in terms of structural forms, regulations to infer the lessons to be learnt by Nepal in the aftermath of Gorkha earthquake. Apart from this, review of structural performance during two major earthquakes of 1934 (MW 8.1) and 1988 (MW 6.5) in Nepal is presented to draw insights in terms of changing structural forms, technology and housing units. Insights are presented in terms of codal provisions and distribution of structures in Nepal. With due account of major world earthquake paradigms and historical earthquakes from Nepal and detailed field reconnaissance after the Gorkha earthquake, interpretations are disseminated in terms of lessons to be learned by Nepal in the aftermath of Gorkha earthquake. Comparative analyses have highlighted the urgent need of building code revision and development of proper strengthening techniques for the affected structures.

Fatality rates of the M w ~8.2, 1934, Bihar–Nepal earthquake and comparison with the April 2015 Gorkha earthquake

Large Himalayan earthquakes expose rapidly growing populations of millions of people to high levels of seismic hazards, in particular in northeast India and Nepal. Calibrating vulnerability models specific to this region of the world is therefore crucial to the development of reliable mitigation measures. Here, we reevaluate the >15,700 casualties (8500 in Nepal and 7200 in India) from the M w ~8.2, 1934, Bihar–Nepal earthquake and calculate the fatality rates for this earthquake using an estimation of the population derived from two census held in 1921 and 1942. Values reach 0.7–1 % in the epicentral region, located in eastern Nepal, and 2–5 % in the urban areas of the Kathmandu valley. Assuming a constant vulnerability, we obtain, if the same earthquake would have repeated in 2011, fatalities of 33,000 in Nepal and 50,000 in India. Fast-growing population in India indeed must unavoidably lead to increased levels of casualty compared with Nepal, where the population growth is smaller. Aside from that probably robust fact, extrapolations have to be taken with great caution. Among other effects, building and life vulnerability could depend on population concentration and evolution of construction methods. Indeed, fatalities of the April 25, 2015, M w 7.8 Gorkha earthquake indicated on average a reduction in building vulnerability in urban areas, while rural areas remained highly vulnerable. While effective scaling laws, function of the building stock, seem to describe these differences adequately, vulnerability in the case of an M w >8.2 earthquake remains largely unknown. Further research should be carried out urgently so that better prevention strategies can be implemented and building codes reevaluated on, adequately combining detailed ancient and modern data.

Preliminary assessment of seismic site effects in the fluvio-lacustrine sediments of Kathmandu valley, Nepal

Seismic site effects are predicted adopting ground response analysis for the fluvio-lacustrine deposits of Kathmandu Valley using available geotechnical data. Equivalent linearization of nonlinear soil model has been analyzed for the study area with the geotechnical database up to the engineering bedrock level. The amplification ratio has been estimated to be varying from 1.9 to 7.8. As the peak spectral acceleration and predominant period largely contribute in the damage of structures, higher values of these parameters are consistent with the damage during 1934 Bihar–Nepal earthquake. The peak spectral acceleration for Kathmandu Valley has been estimated in a close range of 1.2725–1.2826 g. Meanwhile, the predominant period of valley soil varies from 0.27 to 0.61 s, representing the possible resonance, as 3–6 stories structures are the majority constructions in the study area. It has been contemplated that the upper 30 m of Kathmandu Valley soil would undergo large amplification with higher spectral acceleration and the predominant period shows the higher possibility of resonance with the construction trend of the buildings. Past events have shown the severity of damage level during earthquake events in Kathmandu Valley; as the capital city with the highest population density is residing in this area, similar scenario of damage may be witnessed in future events as well, so incorporating the local site effects is must. Thus, the present study provides insights on the level of risk and possible geotechnical basis for the mitigation of inherited earthquake risk in the valley.

The 2015 Gorkha Earthquake and response of the Kathmandu Valley sediments

The Gorkha Earthquake occurred on the gently dipping part of the Main Himalayan Thrust (MHT), close to the Main Central Thrust (MCT). This earthquake possibly occurred in the source zone of the 1833 Nepal Earthquake (Mw 7.6), which occurred after 182 years. The region between the 1905 Kangra Earthquake and 1934 Bihar-Nepal Earthquake has not produced any great earthquake since the last 500 years and still remains a potential site for great earthquake(s) in future. The Kathmandu Valley witnessed moderate ground acceleration and comparatively large velocity as recorded at Kantipath during the Mw 7.8, Gorkha Earthquake. The analysis of the records show that high frequencies were damped and low frequencies were dominant over the sedimentary basin, which can be attributed to the response of the sediments underneath. Because of damping of high frequencies, the engineered, low storey buildings were less damaged and resisted the ground shaking comparatively well. However, on the other hand, the historical monument 'Dharahara' collapsed completely and the high rise apartment buildings suffered more because of the dominance of low frequencies.

Seismic vulnerability and risk assessment of Kolkata City, India

Abstract. The city of Kolkata is one of the most urbanized and densely populated regions in the world and a major industrial and commercial hub of the eastern and northeastern region of India. In order to classify the seismic risk zones of Kolkata we used seismic hazard exposures on the vulnerability components, namely land use/land cover, population density, building typology, age and height. We microzoned seismic hazard of the city by integrating seismological, geological and geotechnical themes in GIS, which in turn are integrated with the vulnerability components in a logic-tree framework for the estimation of both the socioeconomic and structural risk of the city. In both the risk maps, three broad zones have been demarcated as "severe", "high" and "moderate". There had also been a risk-free zone in the city that is termed as "low". The damage distribution in the city due to the 1934 Bihar–Nepal earthquake of Mw = 8.1 matches satisfactorily well with the demarcated risk regime. The design horizontal seismic coefficients for the city have been worked out for all the fundamental periods that indicate suitability for "A", "B" and "C" type of structures. The cumulative damage probabilities in terms of "none", "slight", "moderate", "extensive" and "complete" have also been assessed for the predominantly four model building types viz. RM2L, RM2M, URML and URMM for each seismic structural risk zone in the city. Both the seismic hazard and risk maps are expected to play vital roles in the earthquake-inflicted disaster mitigation and management of the city of Kolkata.

The 25 April 2015 Nepal Earthquake and its Aftershocks

The massive M w = 7.8 earthquake which rocked the Nepal Himalaya on 25 April 2015 is the largest to have occurred in this region in the past 81 years. This event occurred by slip on a ~150 km long and 55 km wide, shallow dipping (~5°) segment of the Main Himalayan Thrust (MHT), causing the Himalaya to lurch southwestward by 4.8 ± 1.2 m over the Indian plate. The main shock ruptured the frictionally locked segment of the MHT, initiating near the locking line and rupturing all the way updip close to its surface expression near the foothills of the Himalaya. The main shock was followed by 41 aftershocks within 26 h, among which a couple were larger than magnitude (M w ) 6.5. These two large aftershocks occurred on fault(s) which had similar orientation as the one that caused the main shock, contributing to strain release along the MHT. The rupture area of the main shock overlaps the meisoseismal zone of the 1833 Nepal earthquake and is immediately to the west of the 1934 Bihar-Nepal earthquake. This region had accumulated ~3 m of slip in the past 182 years, converging at a rate of ~18 mm/yr. The close match of the accumulated slip with the coseismic slip of the main event confirms that majority of the convergence between India and Tibet is stored as elastic strain energy and is released by brittle failure in earthquakes. This Nepal earthquake has highlighted that other segments of the Himalaya too have significant unrelieved elastic strain and may also rupture in similar or greater earthquakes in the future.

Soft sediments and damage pattern: a few case studies from large Indian earthquakes vis-a-vis seismic risk evaluation

India is prone to earthquake hazard; almost 65 % area falls in high to very high seismic zones, as per the seismic zoning map of the country. The Himalaya and the Indo-Gangetic plains are particularly vulnerable to high seismic hazard. Any major earthquake in Himalaya can cause severe destruction and multiple fatalities in urban centers located in the vicinity. Seismically induced ground motion amplification and soil liquefaction are the two main factors responsible for severe damage to the structures, especially, built on soft sedimentary environment. These are essentially governed by the size of earthquake, epicentral distance and geology of the area. Besides, lithology of the strata, i.e., sediment type, grain size and their distribution, thickness, lateral discontinuity and ground water depth, play an important role in determining the nature and degree of destruction. There has been significant advancement in our understanding and assessment of these two phenomena. However, data from past earthquakes provide valuable information which help in better estimation of ground motion amplification and soil liquefaction for evaluation of seismic risk in future and planning the mitigation strategies. In this paper, we present the case studies of past three large Indian earthquakes, i.e., 1803 Uttaranchal earthquake (Mw 7.5); 1934 Bihar–Nepal earthquake (Mw 8.1) and 2001 Bhuj earthquake (Mw 7.7) and discuss the role of soft sediments particularly, alluvial deposits in relation to the damage pattern due to amplified ground motions and soil liquefaction induced by the events. The results presented in the paper are mainly focused around the sites located on the river banks and experienced major destruction during these events. It is observed that the soft sedimentary sites located even far from earthquake epicenter, with low water saturation, experienced high ground motion amplification; while the sites with high saturation level have undergone soil liquefaction. We also discuss the need of intensifying studies related to ground motion amplification and soil liquefaction in India as these are the important inputs for detailed seismic hazard estimation.

Regional level ground motion simulation for a hypothetical great earthquake in the Garwhal Himalaya

The 500–800 km long segment located between the rupture zones of 1905 Kangra (M W 7.8) and 1934 Bihar–Nepal earthquake (M s 8.3) known as central seismic gap has not generated any great event since historic times. The objective of the present study is to simulate displacement time histories in the Garhwal-Himalayan region for a hypothetical great earthquake in the seismic gap using spectral finite element method. The orientation of the rupture plane, slip field and rupture velocity are modelled as random variables and ensemble of ground motions have been simulated. Contour maps of peak ground displacement (PGD) and peak ground residual displacement (PGRD) are provided in the epicentral region. The statistics of PGD at important cities and towns in the epicentral regions have been presented.

Role of Transverse Tectonics in the Himalayan Collision: Further Evidences from Two Contemporary Earthquakes

Abstract: Two contemporary earthquakes originating in the central Himalayan arc and its foredeep (Sikkim earthquake of 18.09.2011, Mw 6.9, h: 10-60 (?) km and Bihar-Nepal earthquake of 20.08.1988, Mw 6.8, h: 57 km) are commonly associated with transverse lineaments/faults traversing the region. Such lineaments/faults form active seismic blocks defining promontories for the advancing Indian Craton. These actually produce conjugate shear faulting pattern suggestive of pervasive crustal interplay deep inside the mountains. Focal mechanism solutions allow inferring that large part of the current convergence across the central Himalayan arc is accommodated by lateral slip. Similar slip also continues unabated in the densely populated foredeep for distances up to several tens of kilometers south of the Main Boundary Thrust (MBT).

Site Effects Estimation in Delhi from the Indian Strong Motion Instrumentation Network

The recent spurt in global earthquake activity has enhanced the consciousness about the increasing vulnerability of large population in the region close to Himalayas and has made significant long‐term social and economic impacts. The observation of strong motion and the investigation of the destruction from these earthquakes provide the disciplines of seismology and earthquake engineering with informative and valuable data, experiences, and lessons and raise a number of important scientific challenges. Himalaya is among the most seismically active regions in the world and has experienced several earthquake disasters during historical times. In the last 50 years, the population of India has doubled and resulted in the very rapid growth of settlements, especially in urban areas. At present, about 50 million people in India, living in the Himalayan region and the adjoining plains, are at risk from earthquakes. During the last 200 years, the Indian peninsula has experienced several great earthquakes with a magnitude above 8.0, namely, the Kutch, Gujarat earthquake (1819); the Assam earthquake (1897); the Kangra earthquake (1905); the Bihar–Nepal earthquake (1934); and the Assam earthquake (1950). Most of the parts of the Himalayas comprising North India and Northeastern India are mapped as either seismic zone IV or V in the seismic zonation map of India (on a scale of II–IV). Two of the recent significant earthquakes in North India are the Uttarkashi earthquake of 1991 ( M w 6.8) and the Chamoli earthquake of 1999 ( M w 6.5). Despite being one of the most seismically active regions of the world, the strong‐motion data set in India is, in general, very sparse. For this reason, the seismic hazard in India, until now, has been estimated using either the intensity data or attenuation relations derived for other regions (e.g., Khattri et al. , 1984; Krishna, 1992). Therefore, in the absence of adequate …

Primary surface ruptures of the great Himalayan earthquakes in 1934 and 1255

It is unclear where plate boundary thrusts generate giant rather than great earthquakes. Along the Himalayas, the source sizes and recurrence times of large seismic events are particularly uncertain, since no surface signatures were found for those that shook the range in the twentieth century. Here we challenge the consensus that these events remained blind and did not rupture the surface. We use geomorphological mapping of fluvial deposits, palaeo-seismological logging of river-cut cliffs and trench walls, and modelling of calibrated 14C ages, to show that the Mw 8.2 Bihar–Nepal earthquake on 15 January 1934 did break the surface: traces of the rupture are clear along at least 150 km of the Main Frontal Thrust fault in Nepal, between 85° 50′ and 87° 20′ E. Furthermore, we date collapse wedges in the Sir Valley and find that the 7 June AD 1255 earthquake, an event that devastated Kathmandu and mortally wounded the Nepalese King Abhaya Malla, also ruptured the surface along this stretch of the mega-thrust. Thus, in the past 1,000 years, two great earthquakes, 679 years apart, rather than one giant eleventh-century AD event, contributed to the frontal uplift of young river terraces in eastern Nepal. The rare surface expression of these earthquakes implies that surface ruptures of other reputedly blind great Himalayan events might exist. The recurrence times of great Himalayan earthquakes are difficult to assess because they rarely rupture the surface. Field mapping and 14C dating of offset fluvial deposits are used to identify two great Himalayan quakes that ruptured the surface along the main plate boundary fault in AD 1255 and 1934.

Seismic hazard assessment of eastern Nepal using 1934 and 1988 earthquakes

The Himalayan arc is widely considered as one of the hot spots in terms of earthquake disaster. Nepal, which is centrally located in the Himalayan region, has witnessed many medium to large earthquakes in the past, e.g., 1934 Bihar-Nepal earthquake, 19 88 Udayapur earthquake. Because of lack of income resources in rural area, considerable number of population has already migrated to the major urban areas of the country and the trend is still continued. With such population pressure and also economic constrains, major part of population is residing in weak and non-engineered structures of the unplanned urban areas. Consequently, it has put large population at high risk of earthquake disaster. It is, therefore, necessary to assess the seismic hazard so that proper mitigation measures may be adopted for the safeguard of the population, property and infrastructures under risk.&#x0D; In this contribution, preliminary Probabilistic Seismic Hazard Analysis (PSHA) for eastern Nepal is carried out taking two point sources, i.e. 19 3 4 Bihar -Ne pal and 1988 Udayapur earthquakes. For Bihar-Nepal earthquake Peak Ground Acceleration (PGA) of 100 gal is computed for southeastern Nepal and exceeds as much as 350 gal near the epicenter. The 1988 Udayapur earthquake having smaller magnitude than 1934 Bihar Nepal earthquake has given maximum 300 gal of PGA. The computed intensities for both earthquakes almost correspond with the observed values. The study, for the first time, provides strong ground motion data at local level and may be useful in designing engineering structures, upgradation of building code and most importantly to formulate policy for earthquake risk management in eastern Nepal.