Roles of subway speed and configuration on subway-induced seismic noises in an urban region

Underground traffic systems are a major generator of high-frequency ground vibrations in urban regions. Subway-induced ground vibrations are identified from seismic records at a seismic station on a designed monitoring site with curved railroad tracks. Subway-induced ground vibrations appear in diffusive and periodic wavelet packets. The ground vibrations are mainly composed of harmonic energy that appears at frequencies in integer multiples of fundamental frequencies. Wheel rotations are a primary source of impulsive signals. The separation distances of wagon wheels lead to the production of periodic time signals. The frequency contents of ground vibrations are controlled by subway speed. The frequency contents are different between outer-circle and inner-circle tracks due to differences in subway speeds, which is consistent over time. The ground vibrations at frequencies >60 Hz are highly affected by ambient noises and vary seasonally. The railway-vehicle configuration and subway speeds modulate the spectral contents. Subway-induced signals are a consequence of various combinations of signals from regularly distributed wagon wheels. The subway speed and wagon configuration can be inferred from the subway-induced signals.