T054-0012
Regional geodetic displacements resulting from the 6.1 Mw Santa Elena Peninsula Subduction Earthquake, 31 March 2019, Ecuador

Wednesday, 16 December 2020
Poster
Patricia A Mothes, National Polytechnical University Ecuador EPN, Quito, Ecuador, Marco Yepez, National Polytechnical University Ecuador EPN, Instituto Geofisico, Quito, Ecuador, Jean Mathieu Nocquet, Université Côte d'Azur, IRD, CNRS, Observatoirede la Côte d'Azur, Géoazur, IRD, CNRS, Valbonne, France, Frederique Rolandone, Sorbonne Université, CNRS-INSU, Institut des Sciences de la Terre Paris, Paris, France and Monica Segovia, Instituto Geofísico, Escuela Politécnica Nacional, Quito, Ecuador
Abstract:
A shallow subduction earthquake struck 15 km offshore of the Ecuadorian resort of Salinas, Santa Elena Province, on 31 March/2019 at 02h04LT, provoking displacements observed in GPS and InSAR interferograms. The thrust movement on the fault plane had a 10 km depth and a 6.1 Mw magnitude. Shaking was widely felt throughout Ecuador, and about 40 aftershocks occurred. Mild building damage in the region resulted. The earthquake is due to strain release at the interface of the subducting Nazca plate.

Co-seismic displacements and continuing afterslip were well registered on the E-W component of permanent GPS stations along the littoral, between 1.7° and 2.5° S. The strongest displacements were registered nearest to the epicenter and showed a robust W-NW trend which continued through 07 Abril, 2019. A ~3 cm displacement was recorded by both Ayangue and Salinas GPS station, both about 30 km from the epicenter. Stations Salango (SLGO) and La Plata (ISPT), 70 km up-coast, registered similar trends with a cumulative 1 cm W-NW displacement. Comparatively, the vertical component is only 60% of that of the horizontal.

InSAR interferometry, using ESA Sentinel-1 satellite images spanning 25 March to 06 April for ascending images and 28 March to 09 Abril for descending images, shows an evident 3 cm westward displacement of the land surface, complementary to GPS trends.

Around early June/2019 three aseismic slow slip episodes registered at five regional GPS stations. This anomaly suggests strong relaxation upon the subduction interface, involving a continuous westward "creep," but not accompanied by marked seismicity.

The Santa Elena Peninsula has experienced earlier class 6 - 7 Mw shallow earthquakes since 1990 (Yepes et al., 2016, Tectonics). In 1933, a 6.9 Mw event struck at La Libertad. However, this is the first geodetic excursion that we have registered in the area.

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