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Subducted oceanic relief locks the shallow megathrust in central Ecuador
Author(s) -
Collot JeanYves,
Sanclemente Eddy,
Nocquet JeanMathieu,
Leprêtre Angélique,
Ribodetti Alessandra,
Jarrin Paul,
Chlieh Mohamed,
Graindorge David,
Charvis Philippe
Publication year - 2017
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2016jb013849
Subject(s) - subduction , geology , seismology , episodic tremor and slip , seamount , bathymetry , trench , tectonophysics , seafloor spreading , tectonics , geophysics , paleontology , oceanography , chemistry , organic chemistry , layer (electronics)
Whether subducted oceanic reliefs such as seamounts promote seismic rupture or aseismic slip remains controversial. Here we use swath bathymetry, prestack depth‐migrated multichannel seismic reflection lines, and wide‐angle seismic data collected across the central Ecuador subduction segment to reveal a broad ~55 km × 50 km, ~1.5–2.0 km high, low height‐to‐width ratio, multipeaked, sediment‐bare, shallow subducted oceanic relief. Owing to La Plata Island and the coastline being located, respectively, ~35 km and ~50–60 km from the trench, GPS measurements allow us to demonstrate that the subducted oceanic relief spatially correlates to a shallow, ~80 km × 55 km locked interplate asperity within a dominantly creeping subduction segment. The oceanic relief geometrical anomaly together with its highly jagged topography, the absence of a subduction channel, and a stiff erosive oceanic margin are found to be long‐term geological characteristics associated with the shallow locking of the megathrust. Although the size and level of locking observed at the subducted relief scale could produce an M w >7+ event, no large earthquakes are known to have happened for several centuries. On the contrary, frequent slow slip events have been recorded since 2010 within the locked patch, and regular seismic swarms have occurred in this area during the last 40 years. These transient processes, together with the rough subducted oceanic topography, suggest that interplate friction might actually be heterogeneous within the locked patch. Additionally, we find that the subducted relief undergoes internal shearing and produces a permanent flexural bulge of the margin, which uplifted La Plata Island.