The steeply subducting edge of the Cocos Ridge: Evidence from receiver functions beneath the northern Talamanca Range, south‐central Costa Rica

Abstract

The deep structure of the south‐central Costa Rican subduction zone has not been studied in great detail so far because large parts of the area are virtually inaccessible. We present a receiver function study along a transect of broadband seismometers through the northern flank of the Cordillera de Talamanca (south Costa Rica). Below Moho depths, the receiver functions image a dipping positive conversion signal. This is interpreted as the subducting Cocos Plate slab, compatible with the conversions in the individual receiver functions. In finite difference modeling, a dipping signal such as the one imaged can only be reproduced by a steeply (80°) dipping structure present at least until a depth of about 70–100 km; below this depth, the length of the slab cannot be determined because of possible scattering effects. The proposed position of the slab agrees with previous results from local seismicity, local earthquake tomography, and active seismic studies, while extending the slab location to greater depths and steeper dip angle. Along the trench, no marked change is observed in the receiver functions, suggesting that the steeply dipping slab continues until the northern flank of the Cordillera de Talamanca, in the transition region between the incoming seamount segment and Cocos Ridge. Considering the time predicted for the establishment of shallow angle underthrusting after the onset of ridge collision, the southern Costa Rican subduction zone may at present be undergoing a reconfiguration of subduction style, where the transition to shallow underthrusting may be underway but still incomplete.

Rapid pulses of uplift, subsidence, and subduction erosion offshore Central America: Implications for building the rock record of convergent margins

“…If half the embayment formed by such underthrusting, estimates of subduction erosion would be halved. However, recent seismic studies do not indicate fl at subduction (Dinc et al, 2010;Dzierma et al, 2011). Moreover, the Osa Peninsula Quaternary deformation does not involve signifi cant subhorizontal shortening (Sak et al, 2009), while Fila Costeña is actively deforming (Sitchler et al, 2007).…”

“…Additional forearc material has also been removed arcward of the embayment (Item DR4). To estimate this, we consider where the upper plate reaches 15 km thickness, ~15 km arcward of the trench (Dzierma et al, 2011) at the place of maximum removal. The triangular pyramidal geometry yields an additional 13,125 km 3 of forearc removal, for a total of 118,125 km 3 .…”

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

“…Arrival time estimations range from 5-1 Ma, but the latest researches place the event at the early Pleistocene (Vannucchi et al, 2013) or late Pliocene (Morell et al, 2014). Hypothesis about the tectonic style include collision (LaFemina et al, 2009), flat subduction (Kolarsky et al, 1995), and steep angle subduction (Arroyo et al, 2003;Dzierma et al, 2011). Shallow or flat subduction is still commonly referred to explain forearc shortening, regional uplift, and Pleistocene decrease and termination of volcanic activity in southeastern Costa Rica (e.g., Fisher et al, 2004;Sitchler et al, 2007).…”

“…Like Protti et al (1994), Husen et al (2003b) also observe a gradual decrease in the maximum depth of the intraslab seismicity from northern to southern Costa Rica, but they did not find evidence of a slab tear. More recently, Dzierma et al (2011) modeled a steeply dipping slab to a depth of approximately 70 to 100 km based on receiver function analysis for the northwestern part of the Talamanca region. Furthermore, local earthquake data from a temporal network show evidence of a steep slab down to ∼ 70 km in southern Costa Rica (Arroyo, 2001;Arroyo et al, 2003).…”

Estado de esfuerzos estáticos en la interface de placas Coco-Caribe en Costa Rica: Interpretación mecánica para el origen de asperezas en la zona sismogénica

“…For central Costa Rica, where the seamount segment of the Cocos plate subducts, local earthquake seismic tomography data by Husen et al (2003), Arroyo et al (2009) and Dinc et al (2010) show a shallower subduction angle. The deep structure of the subduction zone for the Cocos Ridge segment is less constrained with receiver function data by Dzierma et al (2011) and earthquake hypocenter data by Arroyo (2001) and Arroyo et al (2003), showing the presence of a steeply subducting slab down to a depth of 70 km.…”