A source and ground motion study of earthquakes in and near Delhi (the National Capital Region), India

Natural Hazards - We study source parameters of 10 local earthquakes (2.7 ≤  $$M_{w}$$ ≤ 4.5) that have occurred in the National Capital Region (NCR) since 2001 and...     

Determination of seismic wave attenuation in Delhi,India, towards quantification of regional seismic hazard

Natural Hazards - National capital of India, Delhi is under moderate to high seismic hazard due to active regional faults such as the Mahendragarh fault, the Delhi Haridwar fault, the Sohna fault,...     

Strong ground motions from two moderate size (Mw5.5) Kachchh intraplate earthquakes,Gujarat, India

Natural Hazards - During 2006–2016, a strong motion seismic network of twenty 3-component accelerogarphs was deployed by the National Geophysical Research Institute, Hyderabad, India, in the...     

Soft soil mapping using Horizontal to Vertical Spectral Ratio (HVSR) for seismic hazard assessment of Chandigarh city in Himalayan foothills,north India

The populated and expanding city of Chandigarh is located in the foothills of Himalaya, near the potentially active Main Frontal Thrust (MFT). A hazard assessment for this city is consequently of major importance. Thick sediments underlies the city and that can potentially amplify the earthquake shaking and contribute to an earthquake disaster in the city. The present study applies the Horizontal to Vertical Spectral Ratio (HVSR) ambient noise methodology to estimate the resonance frequency of the soft sediments and to obtain a first order estimate of sediment thickness. The study indicates that the soil thickness range from 30 to 270 m and that the resonance frequencies vary from 0.236 to 1.479 Hz. A smooth correlation function between soil thickness and resonance frequency is found, indicating relatively homogeneous soil.     

Different approaches to the seismic hazard of Sannio-Matese (Southern Italy)

The seismic hazard of Sannio-Matese is calculated using a new seismogenetic zoning of southern Italy of seven areas and different, azimuth-dependent, attenuation laws. Various approaches (Gumbel's first and third asymptotic distribution, Cornell) lead to similar results for the different exposure times considered (100 and 200 years) and probability levels (37 and 68%). The present seismic regulation proposed in 1980 by the Italian National Council for Researches, and based on a different approach, is, in general, confirmed by the results.     

Probabilistic seismic hazard assessment for some parts of the Indo-Gangetic plains,India

Natural Hazards - Indo-Gangetic plains are seismically most vulnerable due to the proximity of adjacent great Himalayan earthquakes and thick alluvium deposits of the Ganga River system. As the...     

Local seismic hazard assessment in areas of weak to moderate seismicity—case study from Eastern Germany

Generally the seismic hazard of an area of interest is considered independent of time. However, its seismic risk or vulnerability, respectively, increases with the population and developing state of economy of the area. Therefore, many areas of moderate seismic hazard gain increasing importance with respect to seismic hazard and risk analysis. However, these areas mostly have a weak earthquake database, i.e., they are characterised by relative low seismicity and uncertain information concerning historical earthquakes. In a case study for Eastern Thuringia (Germany), acting as example for similar places in the world, seismic hazard is estimated using the probabilistic approach. Because of the lack of earthquakes occurring in the recent past, mainly historical earthquakes have to be used. But for these the actual earthquake sources or active faults, needed for the analysis, are imprecisely known. Therefore, the earthquake locations are represented by areal sources, a common practice. The definition of these sources is performed carefully, because their geometrical shape and size (apart from the earthquake occurrence model) influence the results significantly. Using analysis tools such as density maps of earthquake epicentres, seismic strain and energy release support this. Oversizing of areal sources leads to underestimation of seismic hazard and should therefore be avoided. Large location errors of historical earthquakes on the other hand are represented by several alternative areal sources with final superimposition of the different results. In a very similar way information known from macroseismic observations interpreted as source rather than as site effects are taken into account in order to achieve a seismic hazard assessment as realistic as possible. In very local cases the meaning of source effects exceeds those of site effects very likely. The influence of attenuation parameter variations on the result of estimated local seismic hazard is relatively low. Generally, the results obtained by the seismic hazard assessment coincide well with macroseismic observations from the thoroughly investigated largest earthquake in the region.     

Probabilistic seismic hazard at the archaeological site of Gol Gumbaz in Vijayapura,south India

Probabilistic seismic hazard analysis (PSHA) is carried out for the archaeological site of Vijayapura in south India in order to obtain hazard consistent seismic input ground-motions for seismic risk assessment and design of seismic protection measures for monuments, where warranted. For this purpose the standard Cornell-McGuire approach, based on seismogenic zones with uniformly distributed seismicity is employed. The main features of this study are the usage of an updated and unified seismic catalogue based on moment magnitude, new seismogenic source models and recent ground motion prediction equations (GMPEs) in logic tree framework. Seismic hazard at the site is evaluated for level and rock site condition with 10% and 2% probabilities of exceedance in 50 years, and the corresponding peak ground accelerations (PGAs) are 0.074 and 0.142 g, respectively. In addition, the uniform hazard spectra (UHS) of the site are compared to the Indian code-defined spectrum. Comparisons are also made with results from National Disaster Management Authority (NDMA 2010), in terms of PGA and pseudo spectral accelerations (PSAs) at T = 0.2, 0.5, 1.0 and 1.25 s for 475- and 2475-yr return periods. Results of the present study are in good agreement with the PGA calculated from isoseismal map of the Killari earthquake, \({\hbox {M}}_{\mathrm{w}} = 6.4\) (1993). Disaggregation of PSHA results for the PGA and spectral acceleration (\({\hbox {S}}_{\mathrm{a}}\)) at 0.5 s, displays the controlling scenario earthquake for the study region as low to moderate magnitude with the source being at a short distance from the study site. Deterministic seismic hazard (DSHA) is also carried out by taking into account three scenario earthquakes. The UHS corresponding to 475-yr return period (RP) is used to define the target spectrum and accordingly, the spectrum-compatible natural accelerograms are selected from the suite of recorded accelerograms.     

Sensitivity analysis of seismic hazard for the northwestern portion of the state of Gujarat, India

We test the sensitivity of seismic hazard to three fault source models for the northwestern portion of Gujarat, India. The models incorporate different characteristic earthquake magnitudes on three faults with individual recurrence intervals of either 800 or 1600 years. These recurrence intervals imply that large earthquakes occur on one of these faults every 266–533 years, similar to the rate of historic large earthquakes in this region during the past two centuries and for earthquakes in intraplate environments like the New Madrid region in the central United States. If one assumes a recurrence interval of 800 years for large earthquakes on each of three local faults, the peak ground accelerations (PGA; horizontal) and 1-Hz spectral acceleration ground motions (5% damping) are greater than 1 g over a broad region for a 2% probability of exceedance in 50 years' hazard level. These probabilistic PGAs at this hazard level are similar to median deterministic ground motions. The PGAs for 10% in 50 years' hazard level are considerably lower, generally ranging between 0.2 g and 0.7 g across northwestern Gujarat. Ground motions calculated from our models that consider fault interevent times of 800 years are considerably higher than other published models even though they imply similar recurrence intervals. These higher ground motions are mainly caused by the application of intraplate attenuation relations, which account for less severe attenuation of seismic waves when compared to the crustal interplate relations used in these previous studies. For sites in Bhuj and Ahmedabad, magnitude (M) 7 3/4 earthquakes contribute most to the PGA and the 0.2- and 1-s spectral acceleration ground motion maps at the two considered hazard levels.     

Assessment of the potential for bank filtration in a water-stressed megacity (Delhi,India)

In the densely populated semi-arid territory around Delhi, the water demand is rising continuously, while the surface- and groundwater resources are threatened by contamination and overexploitation. This is a typical scenario in many newly industrialising and developing countries, where new approaches for a responsible resources management have to be found. Bank filtration holds a great potential, thus being a low tech method and benefiting from the storage and contaminant attenuation capacity of the natural soil/rock. For this study, three field sites have been constructed to investigate bank filtration in different environments in and around the megacity with a main focus on inorganic contaminants. Hydraulic heads, temperature gradients and hydrochemistry of surface water and groundwater were analysed in three different seasons. Depending on site-specific conditions, distinct hydrogeological conditions were observed and both positive and negative effects on water quality were identified. Most concerning issues are the impact of anthropogenic ammonia, the mixing with ambient saline groundwater and the mobilisation of arsenic during the reductive dissolution of manganese- and iron-(hydr)oxides. Positive aspects are the dilution of contaminants during the mixing of waters from different sources, the sorption of arsenic, denitrification, and the precipitation of fluoride under favourable conditions.     

First Order Seismic Microzonation of Delhi,India Using Geographic Information System (GIS)

A first order seismic microzonation map of Delhi is prepared using five thematic layers viz., Peak Ground Acceleration (PGA) contour, different soil types at 6 m depth, geology, groundwater fluctuation and bedrock depth, integrated on GIS platform. The integration is performed following a pair-wise comparison of Analytical Hierarchy Process (AHP), wherein each thematic map is assigned weight in the 5-1 scale: depending on its contribution towards the seismic hazard. Following the AHP, the weightage assigned to each theme are: PGA (0.333), soil (0.266), geology (0.20), groundwater (0.133) and bedrock depth (0.066). The thematic vector layers are overlaid and integrated using GIS. On the microzonation theme, the Delhi region has been classified into four broad zones of vulnerability to the seismic hazard. They are very high (> 52%), high (38–52%), moderate (23–38%) and less ( < 23%) zones of seismic hazard. The “very high” seismic hazard zone is observed where the maximum PGA varies from 140 to 210 gal for a finite source model of M_w 8.5 in the central seismic gap. A site amplification study from local and regional earthquakes for Delhi region using Delhi Telemetry Network data shows a steeper site response gradient in the eastern side of the Yamuna fluvial deposits at 1.5 Hz. The ‘high’ seismic hazard zone occupies most of the study area where the PGA value ranges from 90 to 140 gal. The ‘moderate’ seismic hazard zone occurs on either side of the Delhi ridge with PGA value varying from 60 to 90 gal. The ‘less’ seismic hazard zone occurs in small patches distributed along the study area with the PGA value less than 60 gal. Site response studies, PGA distribution and destruction pattern of the Chamoli earthquake greatly corroborate the seismic hazard zones estimated through microzonation on GIS platform and also establishes the methodology incorporated in this study.     

Stable Isotopic Compositions of Carbonates from the Mesoproterozoic Delhi Supergroup,Northwestern India

Marine carbonate rocks from the Delhi Supergroup show little deviation in whole-rock δ¹³Ccarb values, which are generally around 0% PDB. This narrow range and almost constant δ¹³Ccarb values persist despite close sampling through long, geographically widespread sections. The data suggest that, in contrast to the Neoproterozoic, the global rate of organic carbon burial was probably constant during deposition of the Delhi Supergroup, and perhaps generally during the Mesoproterozoic, as was the redox state of the atmosphere and hydrosphere.     

Kappa (k) derived from accelerograms recorded in the 2008 Wenchuan mainshock,Sichuan, China

High-frequency spectral decay factor, kappa (k), in the accelerograms of the Wenchuan mainshock was measured using strong motion data from 52 stations within 311 km of the epicenter. The derived k range from 0.0034 s to 0.0468 s. The correlation of k versus fault distance was given, which is k = 0.01288 + 5.9068 × 10^–5 R for the N-S component, k = 0.01881 + 1.4219 × 10^–5 R for the E-W component, and k = 0.00855 + 5.6086 × 10^–5 R for the U-D component. The analysis on the spatial variation of k demonstrates that k relates to source effect and propagation effect besides local site effect. Ground motions for the 52 stations were simulated using derived k and compared to actual recordings in terms of waveforms, amplitude spectra and response spectra. The results show agreement at shorter periods (<1 s), but a slight overestimation at longer periods (1–7 s).     

汶川和芦山地震前后浅部应力对深部应力的响应及地震危险性分析

活动断层上盘浅部的高应力异常通常被认为是强震前兆之一,而低应力一般认为不会发生地震是安全的。然而多个震例表明,低应力状态下的地震危险性具有多解性。为进一步探讨强震前的应力异常特征,本研究利用2008年汶川M_S8.0级地震和2013年芦山M_S7.0级地震前的地应力测量结果和地震活动性参数b值,在考虑深部应力对浅部应力影响强度的基础上,建立了浅部应力对深部应力的响应模式,并对强震发生前不同的应力状态与地震危险性的关系进行了讨论。结果表明：活动断层上盘低b值对应浅部高地应力为潜在地震危险区,而对应低地应力则为地震危险性不确定区,需要借助更多的手段进一步确定;2008年汶川M_S8.0级地震前的低应力状态可能反映了区域应力存在较强的调整。本研究对运用断层浅部应力状态评估断层地震危险性具有一定的启示意义。     

Earthquake scenarios: a practical way to handle alternative solutions to historical earthquakes and to increase the transparency of seismic hazard assessment

This study presents a way to handle historical earthquakes whose parameters are based on sparse documentary materials. It is recommended that discrete earthquake scenarios should be constructed in such cases. Scenarios are possible sets of parameters for a past earthquake, reconstructed on the basis of the macroseismic data available. A probability value is to be attached to each of them using expert judgment. This means that uncertainties associated with historical earthquakes become discrete instead of continuous. Assigning a probability value to each scenario and including alternative solutions in the catalogue makes decision-making more transparent. The current state of the art of the research on a given historical earthquake is documented. It is illustrated how seismic histories of a given place are altered when different scenarios of historical key earthquakes are taken into account. The seismic histories consequently have different probabilities. The choice of an appropriate seismic history could be governed by the need: For example, for a high-risk facility, the high-intensity histories have to be considered. Different earthquake scenarios included in the catalogue would permit to evaluate also the uncertainty of the activity rate and to construct the final logic tree.     

Landslide hazard zonation using analytical hierarchy process along National Highway-3 in mid Himalayas of Himachal Pradesh,India

Landslide zonation studies emphasize on preparation of landslide hazard zonation maps considering major instability factors contributing to occurrence of landslides. This paper deals with geographic information system-based landslide hazard zonation in mid Himalayas of Himachal Pradesh from Mandi to Kullu by considering nine relevant instability factors to develop the hazard zonation map. Analytical hierarchy process was applied to assign relative weightages over all ranges of instability factors of the slopes in study area. To generate landslide hazard zonation map, layers in geographic information system were created corresponding to each instability factor. An inventory of existing major landslides in the study area was prepared and combined with the landslide hazard zonation map for validation purpose. The validation of the model was made using area under curve technique and reveals good agreement between the produced hazard map and previous landslide inventory with prediction accuracy of 79.08%. The landslide hazard zonation map was classified by natural break classifier into very low hazard, low hazard, moderate hazard, high hazard and very high landslide hazard classes in geographic information system depending upon the frequency of occurrence of landslides in each class. The resultant hazard zonation map shows that 14.30% of the area lies in very high hazard zone followed by 15.97% in high hazard zone. The proposed model provides the best-fit classification using hierarchical approach for the causative factors of landslides having complex structure. The developed hazard zonation map is useful for landslide preparedness, land-use planning, and social-economic and sustainable development of the region.     

(Re-)Conceptualizing water inequality in Delhi, India through a feminist political ecology framework

This article demonstrates how a feminist political ecology (FPE) framework can be utilized to expand scholarly conceptualizations of water inequality in Delhi, India. I argue that FPE is well positioned to complement and deepen urban political ecology work through attending to everyday practices and micropolitics within communities. Specifically, I examine the embodied consequences of sanitation and ‘water compensation’ practices and how patterns of criminality are tied to the experience of water inequality. An FPE framework helps illuminate water inequalities forged on the body and within particular urban spaces, such as households, communities, streets, open spaces and places of work. Applying FPE approaches to the study of urban water is particularly useful in analyzing inequalities associated with processes of social differentiation and their consequences for everyday life and rights in the city. An examination of the ways in which water practices are productive of particular urban subjectivities and spaces complicates approaches that find differences in distribution and access to be the primary lens for viewing how water is tied to power and inequality.