| Abstract Submission No. | ABS-3.1-0212 |
| Title of Abstract | Preliminary Characterization of Noise Conditions and Variable Site Effects in Uttara Kannada, Karnataka, Using Ambient Noise Analysis |
| Authors | Ch Varun*, K Jahnavi*, Dr. R Thandan Babu Naik, Dr. A Akilan, Dr. HVS Satyanarayana, Dr. B Pradeep Naick, G Vasudevan |
| Organisation | CSIR-NGRI |
| Address | Flat no 105, Parimala Prabhat Apartments, Prabhat Nagar, Chaitanyapuri, Hyderabad Hyderabad, Telangana, India Pincode: 500060 E-mail: chvarun.geo@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Accurate assessment of local seismic site conditions is often constrained in regions with limited earthquake activity and insufficient ground motion data. In such cases, ambient noise analysis offers an effective alternative for understanding shallow subsurface characteristics and potential amplification behaviour. Among available techniques, Power Spectral Density (PSD) and Horizontal-to-Vertical Spectral Ratio (HVSR) methods are widely used to evaluate background noise and site response characteristics. Together, these methods provide a comprehensive understanding of seismic tomography and hazard evaluation. This study examined noise conditions and site effects across Uttara Kannada District, Karnataka. Continuous seismic data from six microseismic stations operated by CSIR-NGRI were used. PSD quantified the amplitude and frequency content of background noise, while HVSR determined the fundamental resonance frequency (f0) and amplification factor (A0), reflecting impedance contrast between shallow layers and bedrock. Continuous waveform data recorded between October 2024 and August 2025 were pre-processed to remove instrumental effects, with each component (Z, N, E) tapered using a cosine function. Data were divided into overlapping segments, and PSD was computed using the Welch method. HVSR was computed as the ratio of horizontal to vertical spectral amplitudes. PSD and HVSR results were compiled for each station, and summary statistics generated to assess spatial variations in noise conditions and local site response. Preliminary results provide insights into ambient noise and site response across the district. PSD shows significant spatial variation in background noise, distinguishing sites based on installation and location. HVSR analysis indicates f0 varies between 0.1 Hz and 19.7 Hz, while A0 varies from 5.0 to 14.0, suggesting heterogeneous subsurface conditions. Temporal analysis reveals seasonal variations in both A0 and f0, with a spike in amplification during monsoon onset, likely due to soil moisture and near-surface velocity contrasts. |
| Keywords | Seismic noise tomography, Power Spectral Density, Amplification, Fundamental frequency |