Aftershocks of the 2016 Mw 7.8 Ecuador Earthquake Reveal Earthquake Cycle is Controlled by Long-Lived Structures
Abstract
Subduction zones produce the largest and most destructive earthquakes on Earth. Moreover, many subduction zones such as the Ecuadorian margin present a diversity of deformation processes including seismic and aseismic slip. The high rate of seismicity that follows a megathrust earthquake allow us to use that seismicity to get a better insight into the seismotectonic processes that take place in such settings. 0n April 2016, a Mw 7.8 megathrust earthquake struck the coast of Ecuador causing vast human and material losses. This earthquake ruptured a ∼100 km-long segment, similar to a previous rupture in 1942. Shortly after the mainshock, we deployed an international temporary network of +60 land and ocean-bottom seismometers that joined the already in-place National Seismic Network of the Instituto Geofisico, to capture the aftershock sequence for the subsequent year. Here we present the results of the processing of this dataset, including the detection and location of more than 10,000 aftershocks and the computation of moment tensors for selected events. Aftershock magnitudes range between 1 to 6.9, and completeness is down to 2.5. As expected, moment tensors show mostly thrust faulting at the interface, but we also observe sparse normal and strike-slip faulting at shallow depths in the marine forearc. The spatial distribution of seismicity delineates the co-seismic rupture area, but extends well beyond it over a +300 km long segment. Main features include three seismicity streaks perpendicular to the trench, at the north, center and south of the mainshock rupture. Notably, a similar seismicity pattern is found during the interseismic period. We observe that this seismicity is spatio-temporally modulated by aseismic slip both during the interseismic and postseismic periods. This common pattern suggests that seismic and aseismic processes are somehow controlled by long-lived features that persist over the earthquake cycle. We propose a bimodal slip model for the Ecuadorian margin, in which the subduction of rough oceanic relief, in this case, the Carnegie Ridge, controls the occurrence of fast and slow slip both in the along-strike and along-dip directions. Our results shed a light on the processes that modulate the earthquake cycle and the occurrence of diverse slip processes in subduction zones.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T52B..04A
- Keywords:
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- 1207 Transient deformation;
- GEODESY AND GRAVITYDE: 7215 Earthquake source observations;
- SEISMOLOGYDE: 8123 Dynamics: seismotectonics;
- TECTONOPHYSICSDE: 8170 Subduction zone processes;
- TECTONOPHYSICS