Separation of High‐ and Low‐Level Ambient Noise for HVSR: Application in City Conditions for Greater Toronto Area

The Nakamura method, which involves horizontal‐to‐vertical spectral ratio (HVSR) analysis, is widely used for seismic microzonation studies. The noise from local traffic in city conditions presents a challenge for the application of HVSR analysis. This article presents a technique developed for separation of the transient noise due to local traffic (high‐level noise) and background ambient noise (low‐level noise) and the application of the HVSR analysis to both partitions of the noise. This approach is applied to identify the predominant frequencies for almost 200 noise samples from the Greater Toronto area. The results demonstrated that the developed technique is effective and allows estimation of the fundamental resonant frequency in the HVSR in urban environment, even in the presence of intensive nearby traffic. The interpretation of the obtained results showed that, most probably, the lower (fundamental) frequency appears due to multiple reflections from the overburden/bedrock boundary. In some cases, a resonance with higher amplitude is dominant, and it is due to a contrast boundary between soil layers in the overburden.