Influence of Incoming Plate Relief on Overriding Plate Deformation and Earthquake Nucleation: Cocos Ridge Subduction (Costa Rica)

Abstract

We present a 2-D P wave velocity model and a coincident multichannel seismic reflection profile characterizing the structure of the southern Costa Rica margin and incoming Cocos Ridge. The seismic profiles image the ocean and overriding plates from the trench across the entire offshore margin, including the structures involved in the 2002 Osa earthquake. The overriding plate consists of three domains: Domain I displays thin-skinned deformation of an imbricate thrust system composed of fractured rocks. Domain II shows~15-km-long landward dipping reflection packages and active deformation of the shelf sediment. Domain III is little fractured and appears to be dominated by elastic deformation, overlain bỹ 2-km-thick landward dipping strata. The velocity structure supports the argument that the bulk of the margin is highly consolidated rock. Thick-skinned tectonics probably causes the uplift of Domains II and III. The oceanic plate shows crustal thickness variations from~14 km at the trench (Cocos Ridge) to 6-7 km beneath the shelf. We combine (1) interplate geometry and fracturing degree, (2) tectonic stresses and brittle strain, and (3) earthquake locations, to investigate relationships between structure and earthquake generation. The 2002 Osa sequence nucleated at the leading flank of subducting seamounts in the area of highest tectonic overpressure. Both estimated rock fracturing and modeled brittle strain steadily increase from the leading flank of the subducting seamounts to their top, reflecting the progressive damage caused by the seamount. Therefore, the seismicity and structural-mechanical evolution of the upper plate reflect the downward propagation of the leading edge of seamounts. Key Points:• Costa Rica Osa margin has three across-strike domains based on structural and physical properties • The bulk of the margin is consolidated rock, fronted by a 20-to 30-km-wide accreted prism • Subducting seamounts correlate with upper-plate strain, overpressure, and earthquakes Supporting Information:• Supporting Information S1

Transient stripping of subducting slabs controls periodic forearc uplift

“…related to glacial/interglacial periods) and the subduction of topographic highs (e.g. seamounts, ridges [46][47][48][49] ) also affect forearc deformation and make the surface evolution difficult to decipher as it interferes with the aforementioned periodic topographic signal obtained despite constant kinematic and boundary conditions (Fig. 3).…”

Geometría de la zona sismogénica interplacas en el Sureste de Costa Rica a la luz de la secuencia de Golfito del 2018

“…Husen et al, 2002;DeShon et al, 2003;Chaves et al, 2017), modelado geodésico (Feng et al, 2012;Kobayashi et al, 2014;Protti et al, 2014) y otros fenómenos sísmicos (Outerbridge et al, 2010). En la transición entre los segmentos Central y Sureste existen solamente un estudio de una secuencia sísmica (Arroyo et al, 2014b) y dos trabajos de sísmica activa (Bangs et al, 2015;Martínez-Loriente et al, 2019). Sin embargo, el segmento Sureste es aún el menos estudiado, debido principalmente a la relativa escasez de cobertura con estaciones sísmicas en el pasado y a la alta dificultad de acceso a la cordillera de Talamanca.…”

Seismic images of the Northern Chilean subduction zone at 19°40′S, prior to the 2014 Iquique earthquake

“…They further suggest that the geological structures found offshore Costa Rica were deformed during seismic slip-to-the-trench events instead of aseismic creep. Post-stack time migration of multichannel seismic data, interpreted together with velocity models from wide-angle seismic profiling, bathymetry and earthquake data (Martínez-Loriente et al 2019) have revealed a clear image of subducted seamounts 18 and 40 km away from the trench, and well resolved tectonic structures in the overriding plate. Here, the M w 6.4 2002 Osa earthquake nucleated at the seamount's leading flank.…”