Geometría de subducción y estructuras corticales: Implicaciones gravimétricas para la sismicidad en la costa ecuatoriana

Abstract

CONDITION FOR PUBLICATION OF PROJECT. The coastal region of Ecuador, located in the subduction zone between the Nazca and South American plates, is characterized by high seismicity due to its heterogeneous seismic coupling. This study aims to analyze the influence of interplate contact geometry, specifically subsurface discontinuities at depth and subduction angles, on the distribution of seismicity and tectonic coupling along the Ecuadorian coast. The methodology included the use of satellite gravimetric data, which were spectrally analyzed, processed in Oasis Montaj, and interpolated in ArcGIS Pro. The results defined different depth levels of the internal configuration of the Ecuadorian coast: The Moho with significant spatial variability, ranging from ~22 km beneath the northern segment to ~64 km in the southern margin, matches with moderate seismic events and weak seismic coupling (Mw. 4.5-4.9; ISC 0.2), particularly in the southeast segment; the Conrad discontinuity, ranging from ~15.6 km in the northern margin to ~37.9 km coincides with historical earthquakes concentrated in northern Manabí and Esmeraldas with high magnitude (Mw. ≥ 7.0) with hypocentral depths between 20 and 33 km suggesting partial decoupling between the upper and lower crust; the upper crustal base with depths between ~6 km and ~15 km, coincides with mapped crustal faults and high coupling indices (ISC > 0.6), indicates localized stress accumulation that might result in future ruptures. It is concluded that these surfaces act as mechanical boundaries governing seismic behavior at different crustal levels, controlling seismic behavior along the Ecuadorian subduction margin., High-magnitude seismicity is concentrated in Esmeraldas and Manabí, and deeper, lower-energy events prevail in Guayas, Santa Elena, and El Oro due to a steeper interplate geometry and weaker upper crustal stress transmission. This work also highlights the value of gravimetric-spectral data in identifying deep crustal discontinuities, providing a robust structural framework that complements GPS and seismological models. Keywords: Ecuadorian margin, Seismic coupling, Gravimetric spectral Analysis, Seismicity, Subduction zone.