Subducted Seamount Locks the Shallow Megathrust in Central Ecuador
Abstract
Among the factors that have been proposed to control the stress accumulation at subduction zones, the role of subducted seamounts is still disputed. Mechanical models suggest that subducted seamounts locally increase the inter-seismic coupling (ISC) along the megathrust and act as seismic asperities. Conversely, seamount subduction has also been associated with weak inter-plate coupling, and highly fractured media, a situation that favors aseismic slip and relatively small earthquakes. However, correlating the location of a subducted seamount with a shallow locked zone has remained a challenge because, where shallow subducted seamounts (< 15 km depth) are imaged, ISC is usually poorly resolved due to the absence of near-trench geodetic data. Here, we use seismic imaging offshore Central Ecuador and detect a shallow, rugged, low-drag shape subducted seamount. Owing to an island and a coastline located respectively 35 km and 50-60 km from the trench, we demonstrate using GPS measurements that the subducted seamount spatially correlates to a local highly coupled asperity within an otherwise dominantly creeping subduction segment. We show that the highly jagged subducted seamount-topography, the absence of a seismically imaged subduction channel and a stiff erosive oceanic margin are the principal long-term characteristics associated with shallow locking of the megathrust. This model may have significant implications on tsunami hazard, and could be tested at worldwide subduction zones.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.G31C..02N
- Keywords:
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- 1209 Tectonic deformation;
- GEODESY AND GRAVITYDE: 1525 Paleomagnetism applied to tectonics: regional;
- global;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8158 Plate motions: present and recent;
- TECTONOPHYSICS