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Distribution of earthquakes in and around the NCT Delhi during January 2001 - March 2020 is shown by the blue circles. The violet curvilinear line shows the Delhi boundary. The seismic stations (SMA and BBS) used in the recording recent events within NCT are depicted.
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An earthquake of small magnitude (ML3.5) occurred on 12 April 2020 near the east district boundary of NCT, Delhi with maximum PGA for the event observed to be 14.13 gals. A few smaller aftershocks also occurred in the area. The estimated fault plane solution of the mainshock suggests normal faulting with some strike slip component. The focal mechan...
Citations
... The mapped lineaments in the region are indicated by dashed lines. Singh et al., 2002;Shukla et al., 2007;Bansal et al., 2009;Pandey et al., 2020). Furthermore, it is undeniable that the Himalayan Thrust system and reactivation of the fault systems of Delhi Fold Belt are the prime causative sources of the seismic hazard in Delhi and adjoining regions (Chandra, 1992;Bilham et al., 2001;Gupta et al., 2013;Shukla et al., 2016). ...
... In a study,~26 bar stress drop was estimated for a relatively small magnitude earthquake (M w 3.5) that had occurred close to the northeastern part of the National Capital Territory of Delhi. Shearer et al. (2006) and Pandey et al. (2020) suggested even higher stress drops for the events of the intraplate origin with the focal mechanism showing relatively a dominant normal faulting. ...
... In the vicinity of the source zone, the prime deformation is observed along the NE-trending ridge fault system, i.e., DHR and MDSSF, characterized by a normal fault with the strike-slip component (Prakash and Shrivastava, 2012). The Sohna and Mathura faults in the region, located to the east of the source zone, were also found to be quite active (Chouhan, 1975;Pandey et al., 2020). The activity might have upsurged the transfer of stresses and their accumulation along the minor active faults/lineaments mapped in the region. ...
Two significant earthquakes (M4.6 and 4.2) occurred close to a NE–SW-trending lineament in the southwestern part of the Delhi NCR (National Capital Region) within a short time span of about 5 months in 2020. These events were located to the north of the Alwar district in Rajasthan and generated a significant ground shaking in and around Delhi. In the present study, we tried to understand a causal relationship between the events and a nearby source in the region, geologically demarcated as the lineament. We analyzed the broadband waveform data from 26 seismic stations that recorded the recent events of 03 July 2020 (M4.6) and 17 December 2020 (M4.2). Typically, the epicentral area has been devoid of significant earthquakes since the past six decades; however, a few minor events (M < 4.0) have been recorded till date. Analysis of the earthquake database for two decades (2000–2022) revealed low seismicity (nearly quiescent-like situation) in ∼100 sq km area around the epicentral zone, unlike considerable seismicity along faults/lineaments close to the Delhi region. The full-waveform inversion analyses of the events indicate normal faulting with a minor strike–slip components. The source parameters, viz., source radius, stress drop, and seismic moment, were estimated to be 6 km, 166 bars, and 8.28E+15 Nm, respectively, for the 03 July 2020 event and 4 km, 138 bars, and 2.29E+15 Nm, respectively, for the 17 December 2020 event. The causative source of these events is ascertained based on the stress inversion modeling that indicated a NW–SE tensile stress corroborating well with the NE–SW-trending lineament mapped in the study region. The static Coulomb stress modeling indicated that the event which occurred on 3 July 2020 had advanced the triggering process of the event in the northeast segment of the same source that occurred on 17 December 2020. We further emphasize that the aforementioned lineament probably activated due to the regional tectonics of the study area. The causative source of these events with strike 48°, dip 86°, and rake −60° is found to be in the conformity with the local tectonics and is well-supplemented by a high stress ratio (0.70 ± 0.05) and low friction coefficient (0.5).
... The April 12 and May 10 quakes occurred on the eastern outskirts of the Delhi NCR region, while the May 29 quake occurred near Rohtak and MDF. The estimated fault plane solutions for the mainshocks of the April 12 and May 10 events indicate normal faulting with a strike-slip component (Pandey et al., 2020;Bansal et al., 2021a). (Figure 3). ...
... The fault plane solution of the last 2 decades is also suggesting that the earthquakes that occurred towards the western side of MDF show strike slip with reverse component (Compression), and the eastern side shows strike slip with Frontiers in Earth Science frontiersin.org normal component (Extensional) (Bansal et al., 2009;Singh et al., 2010;Bansal and Verma, 2012;Pandey et al., 2020;Bansal et al., 2021a) ( Figure 3). Shukla et al. (2007) suggested that the DAFB is bounded towards the west by a prominent strike-slip faults, i.e., Mahendragarh Dehradun Fault (MDF). ...
In recent years, the National Capital Region (NCR) of Delhi has experienced several earthquakes ranging in magnitude from 1.0 to 6.7. According to the last 50 years of earthquake data, the majority of earthquakes in the NCR have occurred near the Mahendragarh Dehradun Fault (MDF) and the Sohna Fault (SF). The region is bounded by a number of subsurface Ridges, Faults, and Lineaments, which are also influenced by the active plate boundary of the Indian and Eurasian plates. Active fault mapping is critical for the precise identification and marking of active fault traces in the NCR area for a precise seismic hazard assessment. We used high resolution Cartosat-1 stereopair data obtained from NRSC, Hyderabad, and Anaglyph (A 3D representation of the surface) and DEM prepared with ENVI software to map the active faults. We identified 12 sites in the NCR region based on satellite data interpretation, primarily along the MDF and Sohna Fault and their extensions. The presence of tectono-geomorphic markers along the MDF and Sohna Fault, such as warped surfaces indicative of fault scarps, stream offsets, gully erosion, and sag ponds, suggests active tectonic movement along these faults, most likely in the recent geological past. We believe the MDF is a right-lateral strike-slip fault with a compressional component on the western side and an extensional component on the eastern side. It acts as a segment boundary between compressional and extensional boundaries. We also identified the right lateral Nuh-Jhirka fault (NJF), which can be the Sohna Fault’s southern extension from Nuh to Jhirka. The western limb of the Delhi Mega fold has also seen a few right-lateral strike-slip movements that have extended up to the eastern bank of the Yamuna River, where the river reflects the base-level change and tight meandering on its upward side and a straight pattern on its downward side. This fault is known as the Delhi Fault (DF). The findings are preliminary, and further research would be required to create a detailed active fault map of the Delhi-NCR region to conduct a precise Seismic Hazard Assessment (SHA) of the region.
... Consequently, our knowledge of the seismicity of the region has improved, revealing a prolific activity of small earthquakes. The seismicity, at least at a small magnitude level, is diffused (Pandey et al. 2020). For this reason, it is not possible to relate events with specific tectonic features; rather the seismicity suggests an active source volume. ...
... These earthquakes were strongly felt in the NCR region and caused panic among the public. Regional moment tensor inversion and source spectrum of the 12 April earthquake as well as an analysis of the ground motion is presented by Pandey et al. (2020). The 12 April and 10 May events were nearly collocated. ...
... According to U.S. Geological Survey Community Internet Intensity Map, which was based on 245 responses, the felt area extended ~35 km south of the NCS epicenter (Table 1). This small magnitude earthquake was felt by a relatively large number of persons considering perhaps because it occurred in the locked-down period of the Covid-19 pandemic when most people were indoors (Pandey et al. 2020;Singh 2020). The earthquake of 10 May occurred near the 12 April hypocenter and had almost the same magnitude. ...
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 the ground motions produced by these events. Moment rate spectra of the earthquakes retrieved from the recordings at hard sites after applying corrections for geometrical spreading (1/R, R ≤ 100 km), anelastic attenuation (Q = 253f0.8) and cutoff frequency (fm = 35 Hz) are reasonably well fit by the Brune ω2-source model with stress drop ranging between 0.9 and 13 MPa. Neglecting the outlier low-stress drop value, the average stress drop is 6 MPa. We apply a modified standard spectral ratio technique to estimate site effect at 38 soft sites in the NCR as well as the geometrical mean site effect with respect to a reference hard site. Application of the stochastic method, with source characterized by the Brune ω2- model with stress drop of 6 MPa and the mean site effect for soft sites, yields peak horizontal ground acceleration and velocity curves that are in good agreement with the observed values. These results provide the parameters needed for the application of the stochastic method to predict ground motions at hard and soft sites in the NCR during postulated \(M_{w}\) ≤ 5.5 earthquakes.
... Shukla et al. 46 used 6 to 10 first motions for estimating the focal mechanism of small-magnitude earthquakes which are insufficient/ and are often difficult to read and focal mechanisms may not be well-constrained 5 . Though Singh et al. 6 emphasized that the focal mechanism estimated by Bansal Table 1 along with the FPS of 12th April 2020 determined by Pandey et al. 48 . Only those stations with cut-off signal to noise ratio >2 in the frequency range of interest are used for estimation of fault plane solutions of these events (Fig. 2). ...
... Fault plane solutions and structural trendsRecently, three earthquakes occurred on 12th April, 10th May and 29th May 2020 were recorded by the more than 22 stations of the National Seismological Network (NSN), distributed in the northern part of India. The fault plane solution (FPS) of the event of 12thApril 2020 event has been estimated by Pandey et al.48 . The NSN has also reported two more earthquakes of M>3.0 on 29th May 2011 and 01st June 2017. ...
Delhi region in northern India experiences frequent shaking due to both far-field and near-field earthquakes from the Himalayan and local sources, respectively. The recent M3.5 and M3.4 earthquakes of 12th April 2020 and 10th May 2020 respectively in northeast Delhi and M4.4 earthquake of 29th May 2020 near Rohtak (~ 50 km west of Delhi), followed by more than a dozen aftershocks, created panic in this densely populated habitat. The past seismic history and the current activity emphasize the need to revisit the subsurface structural setting and its association with the seismicity of the region. Fault plane solutions are determined using data collected from a dense network in Delhi region. The strain energy released in the last two decades is also estimated to understand the subsurface structural environment. Based on fault plane solutions, together with information obtained from strain energy estimates and the available geophysical and geological studies, it is inferred that the Delhi region is sitting on two contrasting structural environments: reverse faulting in the west and normal faulting in the east, separated by the NE-SW trending Delhi Hardwar Ridge/Mahendragarh-Dehradun Fault (DHR-MDF). The WNW-ESE trending Delhi Sargoda Ridge (DSR), which intersects DHR-MDF in the west, is inferred as a thrust fault. The transfer of stress from the interaction zone of DHR-MDF and DSR to nearby smaller faults could further contribute to the scattered shallow seismicity in Delhi region.
... The fault plane solutions provide the geometry and mechanism of the fault from the synthesis of seismic waves generated during the earthquake. The fault plane solutions of both NE Delhi earthquakes (12 th April 2020 of magnitude M w 3.5 and 10 th May 2020 of magnitude M w 3.4) were obtained by Pandey et al. (2020) and Bansal et al. (2020) using the ISOLA software package ( Table 1). The fault plane solutions of both earthquakes have suggested an NNE-SSW trending causative normal fault with a minor strike-slip component. ...
... C2_A and C1_A. The knick zone The NE Delhi earthquakes of 12 th April 2020 and 10 th May 2020 had occurred at a depth of ~ 16km Pandey et al.,2020). The static Coulomb stress changes at a depth of 16 km has been calculated assuming the elastic half-space uniform slip model and considering fault plane solutions of the 12 th April 2020 and 10 th May 2020 earthquakes of magnitude M w 3.5 and M w 3.4, respectively. ...
... The recent aftershocks superimposed over the Coulomb stress largely fall on a high-stress regime, which indicates an NNE-SSW causative source of the 12 th April and 10 th May 2020 events (Figs.5 and 6). The fault plane solutions reported by Pandey et al. (2020) and Bansal et al. (2020) for these earthquakes largely show steep dipping normal faulting with strike-slip component (Fig.7). with strike direction of NNE-SSW (Table 1), corroborating well with the findings of the present study. ...
Recently, amid the pandemic of COVID-2019, the north-east Delhi region experienced two small earthquakes in a short span of 1 month; the first occurred on 12th April 2020 (Mw 3.5) and the other on 10th May 2020 (Mw 3.4). These events were followed by 4 aftershocks of magnitude Mw ≤ 3.0. We carried out morphotectonic (high stream length-gradient index) and static Coulomb stress failure analyses to delineate the hidden causative fault(s) in the region. In the study, ASTER DEM data of 30 m resolution and Survey of India (SoI) toposheets on 1:50,000 scales were used for morphotectonic analysis. The analysis depicted a very high stream length-gradient (SL) and fall in elevation in the epicentral area, suggesting the area to be tectonically active with a NE-SW trending fault line. In addition, the nature of static Coulomb failure stress contours for both the main events, Mw 3.5 and Mw 3.4, suggests an NNE-SSW trending high Coulomb stress regime. Such a high coulomb stress regime is obvious at the location where a high SL index and fall in elevation were marked, which clearly indicates the presence of NNE-SSW trending a causative fault, named ‘Khanpur-Japti fault’.
... The lockdown process slows down the environmental pollution and develops a less polluted ecologically rich society (Bashir et al. 2020;Chakraborty and Maity 2020;Garg et al. 2020;Gupta et al. 2020;Mandal and Pal 2020;Mollalo et al. 2020;€ Ocal et al. 2020;Pandey et al. 2020aPandey et al. , 2020bSaadat et al. 2020;Şahin 2020;Sharma et al. 2020;Shi et al. 2020;Yunus et al. 2020;Zambrano-Monserrate et al. 2020). The restricted transportation system and industrial activities reduce the air pollution level and enhance air quality. ...
Coronavirus disease (COVID-19) has changed the human lifestyle just like a disaster in 2020. Many people died throughout the world due to its severe attack. Lockdown is the most common term used in today's life to prevent the adverse effect of COVID-19. However, during the lockdown period, a significant improvement in the urban environment was noticed in almost every part of the world. During the lockdown period, the decrease in the number of running vehicles and moving people on the road lowers the pollution level and it has a direct positive impact on the urban environment. The study examines the changes found in land surface temperature (LST) and normalized difference vegetation index (NDVI) during the lockdown period in Raipur city, India with the earlier periods (2013–19) to compare the environmental status. The results indicate that the LST is reduced and NDVI is increased significantly during the lockdown period, and the negativity of the LST-NDVI correlation is increased remarkably. The study also shows a better ecological status of the city during the lockdown period. The study is useful for environmental strategists and urban planners.
... We believe that the prevailing lockdown might have reduced the SBN significantly due to sudden pause of countrywide man-made activities. As a result, micro (M1.3, M1.7 and M2.0) to small (M 2.7 and M3.5) earthquakes could be detected accurately at seismic stations (Pandey et al. 2020;Singh 2020). Amidst all the chaos, the planet Earth appears to have got some time to rejuvenate itself. ...
... Similar observations in seismic noise reduction during COVID-19 lockdown are reported globally (Lecocq et al. 2020;Xiao et al. 2020). In the recent Delhi earthquake sequence in April-May 2020, seismic phases from a small magnitude event M3.5 were recorded at more than 29 seismic stations and Latur (LAT) was the farthest station located at about 1100 km away from the source (Pandey et al. 2020). From a close comparison between before and during lockdown situations, we observed a reduction of ambient noise in the short period range during the lockdown. ...
We evaluated seismic background noise at national network in India using PSD, Fourier spectra, Spectrogram, and HVSR approach, before and during the nationwide lockdown declared due to COVID-19 pandemic. The analyses were performed to understand characteristics of noise wave-field in such unprecedented situation and its effect on site response at the station. SBN in long period (> 20 s), primary microseism band (10–20 s) and secondary microseisms (1–10 s) performed well and the noise levels found within the new LNM and HNM. However, in short period (< 1 s) the variation in SBN performance found significant before and during the lockdown. We observed that the SBN at each site in short period (< 1 s) is found to be about 10–12 dB noisier in the time segment prior to the lockdown. The HVSR analysis of SBN at recording sites clearly indicates that the predominant frequency for the entire region remains stable and independent of seismic noise generated before or during lockdown. A substantial variation in amplification factor, however, observed in either situation. Most of the stations across the country experienced diminished cultural noise subsequent to declaration of lockdown on 25 March 2020. Such drastic decrease in cultural noise significantly enhanced the performance of noisy stations, and the best recording stations picked the seismic phases originated from micro to small earthquakes. We suggest installation of seismometers at some depth below the surface, particularly at disturbed sites, may substantially reduce short period noise in earthquake recording.
Northern India's seismic monitoring has advanced significantly in the past with the establishment of a dense and well-distributed network of seismometers. This has greatly enhanced the ability to detect and analyze seismic events in the region and provided a high-quality dataset within the study region. We use a 20-year dataset of 413 earthquakes comprising 3,191 P-arrivals and 2,986 S-arrivals to develop a one-dimensional velocity model for the region. The dataset is meticulously curated based on the azimuthal gap, minimum station requirements, and root mean square travel-time residual. A collection of preliminary models taken from previous studies conducted in and around the central north Indian region is subjected to random perturbations and utilized in a coupled hypocenter and one-dimensional seismic velocity inversion. The model exhibiting a reduced travel time residual in comparison to its predecessors is adopted as the final 1-D velocity model. This final five-layered model up to a depth of 100 km reveals a sediment thickness of 3.5 km with a P-wave velocity of 3.9 km/s and an upper crustal layer down to 20 km with a P-wave velocity of 6.01 km/s, and Moho depth of 42 km with P-wave and S-wave velocities at the Moho of 8.18 km/s and 4.71 km/s, respectively. In defining the local magnitude scale for Central Northern India, we analyzed 166 earthquakes, ensuring each event had at least three synthetic Wood-Anderson amplitudes, with a data set comprised of 1404 maximum amplitudes of S- and Lg waves. The derived ML scale, expressed as =log A (nm) + 0.752 log R (km) + 0.00129 R (km) -1.315+S, has been validated for earthquakes with magnitudes up to 4.6(Mw) over hypocentral distances of up to 1000 km.
The proximity of Delhi and the surrounding region to the active faults along with its geographical settings is a subject of discussion to comprehend the seismic resilience of the capital region of India. The region may be affected by the far-field earthquakes from the Himalayas as well as the near-field earthquakes associated with the local seismic activity. Considering the ordinary settings of this region, the present study is an insight to differentiate the damage potential of ground motion associated with near and far-field conditions to further see their consequences to understand the comprehensive seismic hazard of the region. The acceleration and velocity response analysis of recorded strong ground motions from far-field and near-field earthquakes exhibit a clear distinct behavior in the form of amplification and corresponding predominant period. The comparison of estimated normalized spectral accelerations with that of the seismic design code of the Bureau of Indian Standards (BIS), shows that the current Indian building design code is within the structural limits proposed for the seismic forces of long periods, however, exceeded amplitude of the normalized Spectral Acceleration for far-field earthquakes may be attributed towards the damage potential for the high rise buildings in the capital region of India. On the other hand, near-field earthquakes do not meet the criteria with the design code of BIS at lower periods from 0.02s to 0.09s along with the amplified Spectral acceleration. It also suggests that the structural heterogeneities within the subsurface of Delhi and the surrounding region have a strong bearing in contributing to the impact of seismic waves from near-field earthquakes producing short-period waves that may be disastrous for low-rise buildings. Based on the results, the study region affected by the distinct seismicity patterns is important to understand the shaking behavior of the different kinds of infrastructures/buildings in case of near-field and far-field earthquakes to appropriately utilize the information for constructing new buildings and strengthening the existing infrastructures in Delhi and the surrounding region of India.
