The 2016 Muisne Earthquake and Ecuador's Subduction Zone Geology

Ecuador lies along the convergent boundary where the Nazca Plate subducts beneath the South American Plate at rates of approximately 5–7 cm per year. This tectonic setting, part of the Andean margin, generates frequent seismicity and volcanic activity throughout the country. The coastal region near Muisne experiences elevated hazard due to its position above the locked portion of the subduction interface.

On 16 April 2016 at 23:58 UTC, a magnitude 7.8 earthquake struck 27 km south-southeast of Muisne at a depth of 20.5 km. The event ruptured a segment of the plate interface and produced intense ground shaking along the northern coast. It remains the only magnitude 7.8 or greater earthquake recorded in Ecuador since 1 January 2000.

The rupture occurred within the Ecuador–Colombia subduction segment, a zone that has hosted great earthquakes in the historical record, including the 1906 event estimated above magnitude 8. The 2016 mainshock was followed by an extensive aftershock sequence that illuminated the geometry of the subducting slab. Depth and location data indicate slip on a shallowly dipping thrust fault consistent with the regional plate convergence vector.

Geological studies of the margin highlight the presence of sedimentary basins and accreted oceanic terranes that influence rupture propagation. The relatively shallow hypocenter contributed to significant coastal deformation and tsunami generation, underscoring the tsunami risk associated with interface earthquakes in this region.

Long-term monitoring by regional seismic networks continues to track strain accumulation along the Ecuadorian trench. The 2016 earthquake released a portion of the accumulated elastic strain but left adjacent segments potentially stressed, maintaining the area's elevated seismic potential.

References

USGS Earthquake Catalog
Global CMT Project
Instituto Geofísico Escuela Politécnica Nacional Earthquake Reports