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Structural Controls on Postseismic Deformation Following the Mw 7.8 Pedernales, Ecuador Megathrust Earthquake: Insights from Joint Tomographic Inversion and Aftershock Relocation
  • +12
  • Mariah Hoskins,
  • Anne Meltzer,
  • Josh Stachnik,
  • Hans Agurto-Detzel,
  • Alexandra Alvarado,
  • Susan Beck,
  • Philippe Charvis,
  • Yvonne Font,
  • Stephen Hernandez,
  • Clinton Koch,
  • Sergio Leon Rios,
  • Colton Lynner,
  • Marc Regnier,
  • Andreas Rietbrock,
  • Mario Ruiz
Mariah Hoskins
Lehigh University

Corresponding Author:mac716@lehigh.edu

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Anne Meltzer
Lehigh University
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Josh Stachnik
Lehigh University
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Hans Agurto-Detzel
Géoazur - Université Nice Sophia Antipolis
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Alexandra Alvarado
Instituto Geofísico de la Escuela Politécnica Nacional
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Susan Beck
University of Arizona
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Philippe Charvis
Géoazur - Université Nice Sophia Antipolis
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Yvonne Font
Géoazur - Université Nice Sophia Antipolis
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Stephen Hernandez
Escuela Politécnica Nacional
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Clinton Koch
University of Arizona
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Sergio Leon Rios
Karlsruhe Institute of Technology
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Colton Lynner
University of Arizona
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Marc Regnier
Géoazur - Université Côte d'Azur - IRD - CNRS - Observatoire de la côte d'Azur
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Andreas Rietbrock
Karlsruhe Institute of Technology
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Mario Ruiz
Escuela Politécnica Nacional
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Abstract

The north Ecuador subduction zone exhibits segmentation and clustering of seismicity through megathrust, interseismic, and aftershock seismicity. In 1906, a Mw 8.8 megathrust event ruptured a 500 km segment, portions of which were re-ruptured in ’42 (Mw 7.8), ’58 (Mw 7.7), ’79 (Mw 8.2) and 2016 (Mw 7.8 Pedernales event). Segmentation between the ruptures is caused in part by subducting topography and upper plate structure. Upper plate structure in north Ecuador includes major faults, sedimentary basins and accreted terranes. An international aftershock deployment and the Ecuador permanent network (RENSIG) recorded aftershocks of the 2016 Pedernales event. We performed finite difference tomography in a joint inversion for 3D velocity and earthquake location, using body wave arrivals of aftershocks. The Manabi, Manta-Jama and Borbon sedimentary basins are observed as high Vp/Vs features with the Manabi basin seen as a low Vp and Vs feature. High Vp and Vs are associated with accreted forearc terranes. Relocation of aftershocks in the 3D velocity results in previously described “bands” of seismicity collapsing to smaller clusters ranging from ~8-40 km across. South of the rupture area, a cluster near Manabi collapsed landward, and a cluster appeared west of the trench. Three clusters between the trench and directly south of the rupture contain lower plate and plate interface events. The cluster within the rupture area between the patches of greater slip became more focused, and a cluster became defined on the north side of the northern patch of slip. Two clusters outline subducting Atacames seamounts, with events in the lower plate and interface beneath and in front of the seamounts. North of the rupture, the clusters offshore and onshore near Galera contain mostly interface with some upper plate events. The onshore cluster focused around major faults in a transition from north/south to northeast/southwest structures along the coastal range. Events in the cluster near Atacames relocated mainly in the upper plate, and events in the cluster near Esmeraldas remained in the upper plate. Interseismic events cluster in the same locations as aftershock events. Existing features including upper plate structure and subducting features control and focus both postseismic and interseismic deformation across megathrust cycles.