Density structure and geometry of the Costa Rican subduction zone from 3-D gravity modeling and local earthquake data

Abstract

Abstract. The eastern part of the oceanic Cocos Plate presents a heterogeneous crustal structure due to diverse origins and ages as well as plate-hot spot interactions which originated the Cocos Ridge, a structure that converges with the Caribbean Plate in southeastern Costa Rica. The complex structure of the oceanic plate directly influences the dynamics and geometry of the subduction zone along the Middle American Trench. In this paper an integrated interpretation of the slab geometry is presented based on three-dimensional density modeling of combined satellite and surface gravity data, constrained by available geophysical and geological data and seismological information obtained from local networks. The results show the continuation of steep subduction geometry from the Nicaraguan margin into Northwestern Costa Rica, followed by a moderate dipping slab under the Central Cordillera toward the end of the Central American Volcanic Arc. To the southeast end of the volcanic arc, our preferred model shows a steep, coherent slab that extends up to the landward projection of the Panama Fracture Zone. Overall, a gradual change in the depth of the intraplate seismicity is observed, reaching 220 km in the northwestern part, and becoming progressively shallower toward the southeast, where it reaches a terminal depth of 75 km. The changes in the terminal depth of the observed seismicity correlate with the increased density in the modeled slab. The absence of intermediate depth intraplate seismicity in the southeastern section and the higher densities for the subducted slab in this area, support a model in which dehydration reactions in the subducted slab cease at a shallower depth, originating an anhydrous and thus aseismic slab.

Supplemental Material: Evidence for Caribbean plate subduction in southern Costa Rica

“…Bottom: Transect of seismicity, RF results, and Cocos Plate slab top models. White circles are +3.0 magnitude earthquake events (Linkimer et al, 2018) and red circles are well-relocated earthquakes from Lücke and Arroyo (2015). Green and orange lines are slab tops from Slab2 (Hayes et al, 2018) and Lücke and Arroyo (2015).…”

“…White circles are +3.0 magnitude earthquake events (Linkimer et al, 2018) and red circles are well-relocated earthquakes from Lücke and Arroyo (2015). Green and orange lines are slab tops from Slab2 (Hayes et al, 2018) and Lücke and Arroyo (2015). Black and gold circles show depths of boundaries.…”

Deep Structure of the Continental Plate in the South‐Central Chilean Margin: Metamorphic Wedge and Implications for Megathrust Earthquakes

“…Several studies in recent decades suggest a possible relationship between the structure of the upper plate and the rupture process of megathrust earthquakes in subduction zones. Worldwide, reflection seismic studies (e.g., Bangs & Cande, 1997; Bangs et al., 2020; Geersen et al., 2018; Kodaira et al., 2012; Kopp et al., 2001; Ranero et al., 2006; Tsuji et al., 2013), tomographic inversion of seismic velocities (e.g., Contreras‐Reyes et al., 2012; Klingelhoefer et al., 2010; Martínez‐Loriente et al., 2019; Nakanishi et al., 2002; Sallarès et al., 2013), and density models (e.g., Fleming & Tréhu, 1999; Hackney et al., 2006; Lücke & Arroyo, 2015; Maksymowicz et al., 2015, 2018; Wang et al., 2004; Zhang et al., 2020) show important variations (or segmentation) in the structure of the continental wedge, along the strike and dip direction of the subduction zone. This segmentation seems to control, at least partly, the rate and clustering of the seismicity and the rupture of large earthquakes, including heterogeneities of slip and the distribution of foreshocks and aftershocks (Contreras‐Reyes et al., 2010; Hicks et al., 2014; Maksymowicz et al., 2018; Moscoso et al., 2011; Tsuji et al., 2017; Wang et al., 2004).…”