An assessment of surface versus underground vault installations of broadband seismometers in the hard-rock terrain of the Deccan Volcanic Province, India

Devapriyan Devapriyan, Mrinmoy Tamuli, Arjun Datta, Bivas Das, Vivek Kumar, Rajendra Kumar Dash, Gokul Kumar Saha, Ashish Chaudhary, Dipak Kumar Chaubey, Imtiyaz A Parvez

Surface or ground-level installations of broadband seismic stations are routinely used in temporary seismic networks deployed in the Deccan Volcanic Province (DVP) of peninsular India. In this study, we assess the feasibility and utility of a shallow vault installation in this region, by installing a broadband station in an urban environment, with the sensor placed $\sim 1$ m below ground level. The noise characteristics of this station are compared with those of a co-located station installed at ground level, as well as a temporary station array deployed in rural areas of the DVP during 2024-25. The temporary array is shown to meet international standards of data quality, in terms of observed noise characteristics. However, at periods longer than $\sim 10$ s, the underground vault station, situated in the heart of Pune city, exhibits lower noise levels than all other stations. The difference in noise levels is up to $\approx 17$ dB, and is predominantly seen on the horizontal components of motion, pointing to reduced pressure-induced tilt noise for the vault installation. These findings, though not surprising, serve to quantify the performance enhancement that can be achieved with a small departure from established practices in the field installation of seismic stations.