Abstract
<title>Abstract</title> <p>Whether driven by fluids or aseismic slip, seismic swarms release stress. In the Ecuadorian subduction zone, the 2016 Pedernales Mw7.8 megathrust earthquake caused aftershocks associated with afterslip. It also triggered distant seismic swarms several months after the mainshock. 82 stations were temporarily deployed following the megathrust earthquake. A seismic swarm, approximately 60 kilometers north of the 2016 epicenter, was triggered by the megathrust rupture and occurred 8 months after the mainshock. This upper plate swarm consists of three bursts, each larger in terms of number of events and magnitude. While pore fluid diffusion can explain the migration of the entire sequence, the third burst of seismicity initiated with the largest event (Mw5.4) of the swarm. This event triggered nearby seismicity by stress change and enhanced fluid diffusivity. This event also produced a pressure back front, preventing the occurrence of seismicity near its hypocenter. In northern Ecuador, several Mw5.9 + megathrust events between 2015 and 2025 have loaded the region where a Mw7.7 megathrust earthquake occurred in 1958. Although large megathrust ruptures may result from stress release due to accumulated slip deficit on the plate interface, loading caused by intermediate-sized earthquakes may also contribute to the triggering of larger events.</p>