Evidence for a continental lithospheric mantle earthquake in northern South America

Abstract:

An isolated Mw = 5.7 earthquake, followed by a not very productive aftershock sequence with the largest one having a Mw = 4.2, occurred in a complex tectonic region of northern Southamerica. The mainshock was located at depths between 40-70 km depth, highlighting the question whether the earthquake occurs in the lower crust or the lithospheric mantle. Mantle earthquakes have been observed in the continental lithosphere in various regions (The Himalayas and the Tibetean Plateau, or cratonic areas in the US), but not often in regions of convergence with oceanic lithosphere.

The tectonic setting in northern Southamerica is complex, with an expected flat subduction of the Caribbean plate beneath the Southamerican Plate (SA), and a collision of the oceanic affinity Panama-Choco block about 23 Ma ago against northwestern continental SA with accreted Caribbean affinity terranes. We try to constrain the depth of the Mw = 5.7 earthquake using regional seismic stations, depth phases at regional distances (sP) and teleseismic distances (pP). Our results suggest that the earthquakes are located within the continental lithospheric mantle, below the Moho.

Using other geophysical observables, we evaluate plausible geotherms in the region and study the source process of this earthquake, to help constrain the rheology of the continental lithosphere and tectonic controls of deformation in the region.