Triggered crustal earthquake swarm across subduction segment boundary after the 2016 Pedernales, Ecuador megathrust earthquake

Mariah Hoskins (1) , Anne Meltzer (1) , Yvonne Font (2) , Hans Agurto-Detzel (2) , Sandro Vaca (3) , Frédérique Rolandone (4) , Jean-Mathieu Nocquet (2) , Lillian Soto-Cordero (1) , Joshua Stachnik (1) , Susan Beck (5) , Colton Lynner (6, 5) , Mario Ruiz (3) , Alexandra Alvarado (7, 3) , Stephen Hernandez (3) , Philippe Charvis (2) , Marc Regnier (2) , Sergio Leon-Rios (8) , Andreas Rietbrock (8)

1 Department of Earth and Environmental Sciences [Bethlehem]
2 GEOAZUR 7329 - Géoazur
3 INSTITUTO GEOFISICO AT THE ESCUELA POLITECNICA NACIONAL
4 iSTeP - Institut des Sciences de la Terre de Paris
5 Department of Geosciences [University of Arizona]
6 Department of Earth Sciences [University of Delaware]
7 EPN - Escuela Politécnica Nacional
8 GPI - Geophysikalisches Institut [Karlsruhe]

Megathrust ruptures and the ensuing postseismic deformation cause stress changes that may induce seismicity on upper plate crustal faults far from the coseismic rupture area. In this study, we analyze seismic swarms that occurred in the north Ecuador area of Esmeraldas, beginning two months after the 2016 Mw7.8 Pedernales, Ecuador megathrust earthquake. The Esmeraldas region is 70 km from the Pedernales rupture area in a separate segment of the subduction zone. We characterize the Esmeraldas sequence, relocating the events using manual arrival time picks and a local a-priori 3D velocity model. The earthquake locations from the Esmeraldas sequence outline an upper plate fault or shear zone. The sequence contains one major swarm and several smaller swarms. Moment tensor solutions of several events include normal and strike-slip motion and non-double-couple components. During the main swarm, earthquake hypocenters increase in distance from the first event over time, at a rate of a few hundred meters per day, consistent with fluid diffusion. Events with similar waveforms occur within the sequence, and a transient is seen in time series of nearby GPS stations concurrent with the seismicity. The events with similar waveforms and the transient in GPS time series suggest that slow aseismic slip took place along a crustal normal fault during the sequence. Coulomb stress calculations show a positive Coulomb stress change in the Esmeraldas region, consistent with seismicity being triggered by the Pedernales mainshock and large aftershocks. The characteristics of the seismicity indicate that postseismic deformation involving fluid flow and slow slip activated upper plate faults in the Esmeraldas area. These findings suggest the need for further investigation into the seismic hazard potential of shallow upper plate faults and the potential for megathrust earthquakes to trigger slow-slip and shallow seismicity across separate segments of subduction zones.

Mots clés: triggered seismicity; upper plate deformation; megathrust rupture; postseismic deformation; earthquake swarm; aftershocks

Domaines: Planète et Univers [physics]; Sciences de la Terre

Mariah Hoskins, Anne Meltzer, Yvonne Font, Hans Agurto-Detzel, Sandro Vaca, et al.. Triggered crustal earthquake swarm across subduction segment boundary after the 2016 Pedernales, Ecuador megathrust earthquake. Earth and Planetary Science Letters, 2021, 553, pp.116620. ⟨10.1016/j.epsl.2020.116620⟩. ⟨hal-02966727⟩