Seismic Monitoring in Gujarat, India, during 2020 Coronavirus Lockdown and Lessons Learned

Abstract

The Gujarat region, situated in the westernmost part of India, experienced a deadly intraplate 2001 Mw 7.6 Bhuj earthquake. In the aftermath of the disaster, the Institute of Seismological Research established the Gujarat (India) seismic network in 2006. The network is being operated in online and offline modes, whereas, seismicity monitoring is being done in near-real-time, using data received from the online seismic stations. The Coronavirus disease-19 lockdown provided an opportunity to assess the network reliability in a difficult and challenging scenario. The positive aspect of the lockdown is reflected in signal-to-noise ratio, which improved significantly at all the sites during the lockdown, with more prominent being at sites located on top of the Quaternary sediments due to the absence of high-frequency anthropogenic noise. A sharp fall in the seismic background noise is noticed at most of the stations during the lockdown period, with respect to the prelockdown period. We used the lockdown data to identify other natural sources of noise, besides anthropogenic. The lockdown helped in solving the enigma of seismicity in certain pockets, which turned out to be related to quarry blasts.

Effect of coronavirus lockdowns on the ambient seismic noise levels in Gujarat, northwest India

“…Moreover, in Surendranagar region of Saurashtra, an interesting pattern of no or few seismic events during the lockdown period (Fig. S3 in supplementary material), affirms ISR's claims of quarry blast activity 12 . Thus, the cultural noise reduction due to the lockdown provided a rare opportunity to investigate the effect of anthropogenic noise on the seismic signals in terms of frequency and amplitude.…”

“…The Gujarat State Seismic Network (GSNet), operated and maintained by ISR since July 2006, comprises a dense network of 60 digital BBS and 54 digital strong motion accelerographs (SMA) in the seismically active northwestern region of India 12 . Out of these, 49 permanent seismic stations, equipped with 120 s triaxial broadband sensors connected to 24-bit digitizers, record data at 50 samples per second (sps), and transmit in real time to the data center in ISR, through very small aperture terminal (VSAT) transmission.…”

“…The GSNet was initiated in the aftermath of the disastrous 2001 Bhuj earthquake (Mw 7.7), to monitor seismic activity. This was strengthened in a phased manner with the addition of BBS and SMA stations to the original network of 22 BBS and 43 SMA 12,13 . At present, 25 broadband seismographs (BBS) are operating in a continuous mode in the seismically active zone of Kutch region (popularly called as Kutch Seismic Zone, KSZ), and 10 of these stations are located at an epicentral distance of ~ 50 km from the 2001 Bhuj earthquake (Figure S1).…”

“…At present, 25 broadband seismographs (BBS) are operating in a continuous mode in the seismically active zone of Kutch region (popularly called as Kutch Seismic Zone, KSZ), and 10 of these stations are located at an epicentral distance of ~ 50 km from the 2001 Bhuj earthquake (Figure S1). All stations are located in the same environmental conditions and have the same technical specifications [12][13][14] .…”

“…The lockdown measures taken worldwide led to a reduction in the seismic background noise, enabling better detection of microearthquakes using surface seismometers 1,3 . Similarly, during the lockdown in India, many microearthquakes in the magnitude range of 0.6 to 1.5 have been detected in the seismically active Kutch seismic zone (KSZ), Gujarat, using data recorded by the Institute of Seismological Research (ISR) seismic network 12 , as shown in supplementary Figures S1 and S2. Moreover, in Surendranagar region of Saurashtra, an interesting pattern of no or few seismic events during the lockdown period (Fig.…”