The disturbing influence of small earthquakes on tectonic tremor synchronization

Gaspard Farge, & Emily E. Brodsky

Published September 8, 2024, SCEC Contribution #13745, 2024 SCEC Annual Meeting Poster #071

Tectonic tremor's activity locally displays strikingly regular patterns of recurrence in space and time. Those patterns reveal that tremorgenic faults can synchronously activate in hundreds-of-kilometer-wide segments, and with a consistent periodicity over many recurrence cycles. Tremor zones are often clearly segmented, some segments activating synchronously in large, regular bursts, others with less regularity, in desynchronized, smaller bursts.

Tremor activity is known to be sensitive to dynamic stresses from passing seismic waves of large amplitude from distant large earthquakes and smaller regional events. In rare places, it has been shown that small (M~2) earthquakes can trigger tectonic tremor activity. The relatively frequent activity of those small earthquakes therefore has the potential to significantly perturb the otherwise regular recurrence of tremor events.

We show that in the tremor zones across the world (Cascadia, Nankai, Eastern Alaska, Hikurangi, Parkfield) segments where tremor is most synchronized into regular, large-scale patterns coincide with low crustal earthquake activity. This correlation seems to explain about 10–20% of the spatial variance of tremor synchronization, especially when the earthquake activity is high, and outweighs other segmentation factors.

We interpret this result as emerging from the competition between the internal dynamics ruling tremor activity, pushing it towards synchronization, and the external perturbation by small earthquakes, locally throwing parts of the fault out of synchronicity, thus preventing larger-scale collective activation. We model this competition in a perturbed, pulse-coupled oscillator system, which reproduces well the anticorrelation between perturbation rate and synchronization intensity. Our results indicate that local earthquake activity should be considered as a significant factor shaping the segmentation of tremor intermittence. They paint the picture of complex interactions between seismic and aseismic processes in faults and across their close environment, where the activity of one generates a landscape of constraints for the other to develop.

Citation
Farge, G., & Brodsky, E. E. (2024, 09). The disturbing influence of small earthquakes on tectonic tremor synchronization. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology