Ambient noise levels in Gujarat State (India) seismic network

Abstract

The Gujarat state seismic network (GSNet), comprising of 50 broadband seismograph (BBS) stations and 40 strong motion accelerographs (SMAs), has been operated and maintained by the Institute of Seismological Research (ISR) since 2006. Nineteen permanent BBS stations are connected through VSAT and the rest are kept in an offline mode. The local geology beneath seismic stations varies from Mesozoic to Quaternary formations. The seismic background noise (SBN) at these stations was calculated and found that it varies widely as a function of period, time and geographic location. We have studied the SBN variation along these three parameters for 14 online BBS stations of the GSNet. It was found that the stations located on the Deccan trap and Mesozoic formations are good sites with low SBN while stations on Quaternary, Tertiary and soft soil are noisy. The comparison between day and night noise spectra shows that SBN increases during the daytime at most of the stations. Three typical noisy peaks at three different periods were recorded at all of the stations, which is a global phenomenon. The results of this study will be helpful in selecting sites for future earthquake observations.

Appraisal of seismic noise scenario at national seismological network of India in COVID-19 lockdown situation

“…At higher frequencies body waves make a significant contribution to seismic noise (e.g., Roux et al 2005;Koper et al 2010;Landes et al 2010;Wang et al 2010). Various researchers have also observed short period noise well recorded on vertical component, and long period noise prominent on horizontal components of the seismic records (Webb 2002;Kumar et al 2012;Jana et al 2017). De Angelis (2008, however, argued that the horizontal components are noisier than the vertical components due to its sensitivity to the tilts of the seismometers, as the gravity effect is coupled to the horizontal components only.…”

Comparison of earthquake source characteristics in the Kachchh Rift Basin and Saurashtra horst, Deccan Volcanic Province, western India

“…The Deccan trap sites show lesser noise levels, while sites on Jurassic, Cretaceous, and Tertiary formations show moderate noise levels. An earlier study by Kumar et al (2012) using data from 14 broadband seismic stations revealed that stations on soft soils are noisier. A careful comparison between the previous seismic noise level analysis based on data from limited stations and the present analysis with larger amount of data recorded by more seismograph stations for longer duration, provides detailed information about the background noise level of the Gujarat seismic network.…”

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

“…2b and 3a). Previously, large seismic background noise values in the 2-5 Hz frequency range for stations located on the Quaternary and Tertiary formations were reported 20 , and explained in terms of a combined effect of predominant frequencies and cultural activities. Here, the predominant frequency corresponds to the frequency at which the maximum value of site amplification is observed for a station/site.…”