A widely felt Tremor (M_L3.5) of 12 April 2020 in and around NCT Delhi in the backdrop of prevailing COVID-19 pandemic lockdown: analysis and observations

Abstract

An earthquake of small magnitude (M L 3.5) 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 mechanism corroborates with the NE-SW orienting lineaments mapped in the region near the epicenter. The source parameters of the event, namely, seismic moment, stress drop, corner frequency, and source radius are estimated to be 1.15 x 1014 N-m, 25.7 bars, 5.7 Hz and 300 m, respectively. The decay rate of acceleration with epicentral distance suggests a regression relation PGA ¼ 474 D À1.347, which may be useful for understanding the ground motion in the region. A noise analyses at NDI rock and UJWA soil sites clearly suggest a significant reduction in ambient noise by $10 dB in the frequency band (1.0-10.0) Hz at the respective sites, during the COVID-19 lockdown situation. The reductions of the noise level improve the signal to noise ratio substantially at all the seismic stations located in the urban agglomerations, which enabled the recording of clear phases of the event and hence improved the analysis.

COVID-19 lockdown effect on land surface temperature and normalized difference vegetation index

“…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.…”

Delineation of the Causative Fault of Recent Earthquakes (April-May 2020) in Delhi from Seismological and Morphometric Analysis

“…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).…”

“…C2_A and C1_A. The knick zone (Bansal et al, 2020;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 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.…”

A holistic seismotectonic model of Delhi region

“…Recently, 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.…”