Although train-induced vibrations are mainly regarded as a source of unwanted noise for classical seismological applications, these vibrations act as powerful sources for modern seismic methods that use ambient noise for seismic imaging and monitoring.
As part of PACIFIC – Passive seismic techniques for environmentally friendly and cost-effective mineral exploration – the Dublin Institute for Advanced Studies (DIAS) is investigating train-induced vibrations generated by (1) numerical modeling and (2) real data recorded using seismic sensors to better understand the nature of the signal and appropriate use of this signal for seismic imaging and monitoring.
In the first part, DIAS presented a simple approach for modeling train-generated seismic signals inspired from early work in the engineering community, which assumes that seismic waves are emitted by sleepers regularly spaced along the railway and excited by the passage of the train wheels. DIAS identified two end-member mechanisms that generate spectral signatures very similar to the two categories of observations mentioned in the seismological literature. For more details please refer to the following link on Research Gate.
In the second part, DIAS is trying to develop new environmentally friendly ways of monitoring ground integrity using ground vibrations made by passing trains. This part involves the recording and analysis in detail the seismic vibrations generated by trains to better understand the proprieties of the waves propagating from the railway trough the shallow underground.
As a pilot test, DIAS deployed 26 three-component seismographs along a railway (24 stations-50m spacing-deployed along and two stations perpendicular to the railway) and recorded ambient noise signals for three days. DIAS has been able to distinguish between different train types (e.g. cargo vs. passenger trains) and train lengths (3-4, 5-6, 7-9, and/or 10-11 wagons). Results of seismic interferometry applied on the pilot test data document a successful retrieval of reflection image and show interfaces consistent with nearby active seismic (~2km in the east of the study area) profile. For more details please refer to the following link on Research Gate.
Since the result of the pilot test train experiment documented a successful imaging of subsurface structure, DIAS is planning to carry out two additional phases in 2020. (1) Repeat the pilot test train experiment in the same location but with 5-10m station spacing and also execute the active hammer seismic in that location and (2) carry out another experiment with 5-10m station spacing in the location of existing active profile and boreholes, where the railway is in ~2km distance, but they do have some additional local noises (city traffic and industry park noises). 80-120 sensors, 1 and/or 3 component nodes in addition to the 26 short-period seismometers will be used.