Numerical Modelling of Train-Induced Seismic Noise: Implications for Passive Seismic Imaging and Monitoring
Abstract
Trains are now recognized as powerful sources for seismic interferometry, but the optimal use of these signals requires a precise understanding of their source mechanisms. Here we present a simple approach for modelling train-generated signals inspired by the engineering literature, assuming that seismic waves are emitted by crossties (or sleepers) regularly spaced along the railway and excited by the passage of train wheels. This approach results in tremor-like emergent signals with harmonic spectra, which reproduces well the main characteristics of seismological observations, although not their absolute amplitudes. We illustrate how the spectra are modulated by wheel spacing, and how their high-frequency content is controlled by the distribution of axle loads over the rail, which mainly depends on ground stiffness beneath the railway, an effective parameter that may reflect rail/ground coupling. We formulate a simple rule of thumb that predicts the frequency bands where most of train-radiated energy is expected, as a function of train speed and geometry. Furthermore, we identify two end-member mechanisms —single stationary source vs. single moving load— which depend on sleeper regularity (i.e. on the properties of the railway infrastructure) and that explain two types of documented observations, characterized by different spectral signatures. We compare our modelling results with experimental data acquired in a controlled configuration, in order to calibrate them in terms of absolute amplitudes. Finally, we discuss the parameters that control the amplitudes of the resulting signals, and therefore our capability to detect them. An important conclusion is that the frequency content of the signals is dominated by high-frequency harmonics and not by fundamental modes of vibrations. Consequently, most train traffic worldwide is expected to generate signals with a significant high-frequency content that can be used for seismic applications. By proposing a framework for predicting train-generated seismic wavefields over meters to kilometers distance from railways, this work paves the way for high-resolution passive seismic imaging and monitoring at different scales with applications to near-surface surveys, natural resources exploration, and natural hazard studies.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMS022...03L
- Keywords:
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- 7203 Body waves;
- SEISMOLOGY;
- 7255 Surface waves and free oscillations;
- SEISMOLOGY;
- 7270 Tomography;
- SEISMOLOGY;
- 7299 General or miscellaneous;
- SEISMOLOGY