Characterizing the Forearc Basement and Subducting Structures of the Northern Ecuadorian Margin

Abstract

We present 2D P‐wave velocity (Vp) models from the northern Ecuadorian subduction zone, north of the Carnegie Ridge. Data were collected during the HIPER2 3D wide‐angle seismic experiment, both onshore and offshore. Key seismic profiles were manually picked to determine P‐wave first‐arrival times, which were used for a traveltime tomographic inversion based on a Bayesian approach. Interpreting these 2D Vp models jointly with existing multi‐channel seismic (MCS) data reveals a high vertical Vp gradient (>0.85 km/s/km) consistent with the position of the forearc basement defined by MCS data, allowing us to map the basement along the margin. In addition, two notable low‐velocity zones are identified. The first zone observed across all profiles within the inner margin wedge, is interpreted as resulting from rock fracturation and/or alteration near the trench. The second one present in the subducting oceanic crust, is characterized by a Vp reduction of 0.5–1.0 km/s relative to the surrounding areas and marks the northern termination of a previously identified trench‐parallel velocities anomaly. As a possible origin of this distinctive anomaly, we propose the entry into subduction of an unmapped fracture zone (FZ), potentially reactivated by the increased plate bending due to the presence of the 2 km‐high Carnegie Ridge. Three FZ are proposed as possible sources of this anomaly that would southwards extend fossil transform faults for 100–150 km.