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Communication Dans Un Congrès Année : 2022

Seismic imaging across a slow slip event area, along the Ecuadorian subduction zone

Alexandra Skrubej
A. Galvé
Mireille Laigle
Alessandra Ribodetti
  • Fonction : Auteur
  • PersonId : 1127751
Laure Schenini
L. Combe
  • Fonction : Auteur
  • PersonId : 752975
  • IdHAL : laure-combe
Davide Oregioni
  • Fonction : Auteur
Hans Agurto‐detzel

Résumé

The Mw 8.8 1906 earthquake that occurred at the Ecuador-Colombia subduction zone is the 7th largest event ever recorded worldwide, and one of several large earthquakes that have affected the region since then. At its southern border, episodes of aseismic slip have been recorded at the shallow updip part of the subduction interplate fault, in the form of both slow slip events (Vaca et al., 2018) and afterslip in the aftermath of the 2016 Mw 7.8 Pedernales earthquake (Rolandone et al., 2018). During the geophysical experiment HIPER, in march 2020, 47 Ocean Bottom Seismometers (OBS) have been densely deployed along a 93-km-long trench-normal profile, crossing the supposed area of the SSE event below the margin. These OBSs recorded the shots produced by 4990 cu.in. airguns, with the R/V Atalante, in order to obtain a high-resolution P-velocity 2D profile. A coincident Multi-Channel Seismic (MCS) profile was acquired, providing information on the structure of the oceanic crust (see companion abstract by Schenini et al.). The combined inversion of the first-arrival and oceanic Moho reflection PmP phases, using the traveltime tomography Tomo2D code (Korenaga et al., 2000), provides both the P-velocity structure of the subducting and upper plates as well as the oceanic Moho geometry down to 20 km depth. The obtained velocity model displays a low-velocity anomaly within the Nazca plate’s oceanic crust at the trench together with a strong increase of the oceanic crust thickness over a distance of only 50 km (from 5.5 km to 16 km thick). The thickened crust in our profile shares a clear seismic signature affinity with the nearby aseismic Carnegie Ridge, resulting from the interaction between the Galapagos hotspot and the Cocos-Nazca Spreading Center (CNSC), 20 Myr ago. Taking this into account, our results nevertheless show a low-velocity anomaly of 11% at the trench which is higher than Vp anomalies observed before the trench in other subduction zones, that have been related to oceanic crust hydration, favored by bending faults. This may thus be an indication of excessive fracturing and hydration of this thicker oceanic crust portion of the Carnegie aseismic ridge. Next steps will be to better understand the influence of this feature on the slipping behavior, by observing the coincident and adjacent MCS profiles.

Domaines

Tectonique
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Dates et versions

insu-04288486 , version 1 (16-11-2023)

Identifiants

  • HAL Id : insu-04288486 , version 1

Citer

Alexandra Skrubej, A. Galvé, Mireille Laigle, Andreas Rietbrock, Alessandra Ribodetti, et al.. Seismic imaging across a slow slip event area, along the Ecuadorian subduction zone. American Geophysical Union, Fall Meeting 2022 (AGU 2022), American Geophysical Union, Dec 2022, Chicago, United States. pp.T53B-02. ⟨insu-04288486⟩
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