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Rapid Migration of Seismic Swarms in the Central-north Ecuadorian Subduction Zone Revealed by Deep Learning and Dense Seismic Arrays

Description: 

The Ecuadorian subduction zone has hosted multiple Mw 7.7–8.8 megathrust earthquakes (1906, 1942, 1958, 1979, 2016), with the 2016 event re-rupturing the 1942 patch. Many seismic swarms and slow-slip events related to structures in the subducting and the overriding plates have occurred along this margin. During 2016-2017, swarm-like aftershocks were recorded by temporary and permanent stations up to ~90 km inland. Nodal arrays were deployed in 2020 and 2022, and 59 broadband stations operated in 2021-2022 from the coast to the Andes foothills. Between 15 March and 9 April 2022, we detected and located more than 200 earthquakes (excluding the 2022 Atacames mainshock–aftershock sequence) using deep-learning-based methods. These events were further refined in a high-resolution 3D velocity model derived from the nodal arrays and relocated with the HypoDD algorithm, producing an unprecedentedly detailed image of local seismicity.

Offshore seismicity occurred in both the southern and northern 2016 slip patches. On 16 March, a two-hour swarm (M < 2) began at shallow depths (< 5 km) in the overriding plate, then extended to 10–25 km in the subducting plate, migrating northward over time. On 17 March, a 2.5-hour swarm (M < 4) occurred in the northern slip patch of the 2016 rupture area, with events deepening with time from ~10 to 30 km across the plate interface and migrating north. The northern swarm follows a U-shaped pattern similar to the near-trench re-entrant scarp of the Atacames seamounts, above and on the eastern front of a high-velocity zone (Vp 7.6–8.0 km/s), likely reflecting the roots of the seamounts. Migration velocities of the events (~9 km/hr southern swarm and ~6 km/hr northern swarm) over short durations indicate slow-slip-driven behavior near the threshold for fluid-driven mechanisms. Neither sequence fits a hydraulic diffusion model; instead, they appear self-driven, with each new rupture nucleating near the high-stress tip of the previous one. Rapid swarm migration likely reflects stress transfer between adjacent ruptures, likely aided by aseismic slip.

Session: Advanced Geophysical Observations, Analytical Methods, and New Insights for Earthquake Swarms [Poster]

Type: Poster

Date: 4/15/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Gabriela

Student Presenter: Yes

Invited Presentation: 

Poster Number: 117

Authors