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Synchronous Seismic Sequences and Slow Slip Events along the South America Subduction Zone

Session: Subduction Processes Along Latin America Subduction Zones I

Type: Oral

Date: 4/19/2021

Presentation Time: 09:45 AM Pacific

Description: 

While episodic tremor and slow slip events (ETS) downdip of the highly-locked portion of the subduction interface have been extensively studied, the South America subduction zone hosts a somewhat different strain release process where Slow Slip Events (SSE) are accompanied with intense micro-seismicity, that we hereafter referred as S5 (Synchronous Seismic Sequence and Slow Slip).

Such a S5 was first observed at shallow depth (10 km), where Vallée et al. (2013) document a one week long SSE of equivalent magnitude 6.1-6.3. Synchronous seismic swarm appears organized into families of repeating earthquakes, progressively activated as slow slip develops. A longer sequence was also documented at immediately north of the rupture of the Mw 7.8 2016 Pedernales earthquake (Vaca et al., 2018). For both events, seismicity accounts for only a few percent of the total moment release.

In northern Peru, a two months long sequence in 2009 generated several moderate earthquakes (Mw~6) that together account for about 25% of the total moment (Mw 6.7) released during the sequence (Villegas et al., 2016). A peculiar aspect of this sequence is that slow slip drastically accelerated after a Mw 5.8 earthquake, suggesting that successive interactions between seismic and aseismic slip controlled the evolution of the sequence.

Finally, a seismic sequence in the Atacama segment (Chile) initiated by a Mw 6.9 mainshock, (Klein et al., submitted). The sequence lasted several weeks with abnormally large aftershocks up to Mw 6.4 and was associated to unusually large post-seismic slip, equivalent to Mw 6.8 developing in low coupling areas.

Unlike ETS, S5 usually occur at seismogenic depth, but at the edges of large locked asperities. Therefore, these processes span lateral changes in friction properties, rather than a transition with depth as ETS do. S5 highlight the evolving interplay between seismic and aseismic slip during the sequence, making them good observational targets to understand the physics of slip at faults.

Presenting Author: Jean-Mathieu Nocquet

Student Presenter: No

Authors