Sources of Long‐Range Anthropogenic Noise in Southern California and Implications for Tectonic Tremor Detection

Asaf Inbal, Tudor Cristea-Platon, Jean-Paul Ampuero, Gregor Hillers, Duncan Agnew, & Susan E. Hough

Published October 16, 2018, SCEC Contribution #8204

We study anthropogenic noise sources seen on seismic recordings along the central section of the San Jacinto fault near Anza, southern California. The strongest signals are caused by freight trains passing through the Coachella Valley north of Anza. Train-induced transients are observed at distances of up to 50 kilometers from the railway, with durations of up to 20 minutes, and spectra that are peaked between 3 and 5 Hz. Additionally, truck traffic through the Coachella Valley generates a sustained hum with a similar spectral signature as the train transients, but with lower amplitude, and wind turbines in northern Baja California introduce a seasonal modulation of 1 to 5 Hz energy across the Anza network. We show that the observed train-generated transients can be used to constrain shallow attenuation structure at Anza. Using the results from this study as well as available borehole data, we further evaluate the
performance of approaches that have been used to detect non-volcanic tremor at Anza. We conclude that signals previously identified as spontaneous tremor were either generated by other identifiable sources, including trains, or were likely false detections.

Citation
Inbal, A., Cristea-Platon, T., Ampuero, J., Hillers, G., Agnew, D., & Hough, S. E. (2018). Sources of Long‐Range Anthropogenic Noise in Southern California and Implications for Tectonic Tremor Detection. Bulletin of the Seismological Society of America,. doi: 10.1785/0120180130.