Long-Period Long-Duration Events Detected by the IRIS Community Wavefield Demonstration Experiment in Oklahoma: Tremor or Train Signals?

In this study, we apply a recently developed local similarity method to detect long‐period long‐duration (LPLD) seismic events using 1‐month continuous waveforms recorded by a nodal array from the Incorporated Research Institutions for Seismology (IRIS) community wavefield experiment in Oklahoma. The local similarity method detects seismic events by correlating waveforms at each station with its neighboring stations. Using this method, we visually identify 21 potential tremor‐like LPLD events lasting more than 300 s during the 1‐month period. However, with beamforming analysis, we find that the source locations and waveform characteristics of these events are consistent with train‐generated seismic signals from the nearby Union Pacific railway. Additional evidence includes amplitude decay away from the railway track, and similarities in frequency–time contents with other confirmed train‐generated seismic signals. This case study highlights the need of dense‐array observations to distinguish between natural and anthropogenic LPLD seismic signals.