Seismic Ambient Noise Analysis of the Indian Subcontinent

Seismic ambient noise has three bands- cultural noise, microseism noise, and infra-gravity waves. In this study, we have considered two bands: cultural noise and microseism noise. Anthropogenic activities generate cultural noise(1-10Hz), whereas ocean, atmosphere, and solid earth interaction lead to the genesis of microseism noise (0.05-1Hz). Our study region is on the Indian subcontinent. We have taken continuous data from the National Center for Seismology, including stations from inland, island, and coastal parts of the subcontinent. A frequency-dependent polarization method is applied. From our observations, the seismic stations located in the busiest part of the city show a high amplitude of noise in the cultural noise band.   Diurnal variations are also observed in this band. However, for stations located in the crowded part of the city, the noise level remains high even at night due to the active nightlife in the cities.  Seasonal variations are not observed in the cultural noise band. In the microseism band, seasonal variations are observed in both the direction of the noise source and the amplitude of noise due to the significant contribution of the southwest monsoon to the Indian subcontinent. For island stations, the peak in the noise is observed in the microseism band, while in the land stations, cultural noise dominates. Sudden increases in the amplitude of microseism noise are detected in the coastal stations because of the disturbed sea-state conditions during the cyclone period. Overall, our study provides a comprehensive idea about the distribution of seismic ambient noise in the Indian sub-continent.