The Costa Rican convergent margin has been considered a type erosive margin, with erosional models suggesting average losses up to −153 km³/km/m.y. However, three‐dimensional (3D) seismic reflection and Integrated Ocean Drilling Program data collected offshore the Osa Peninsula images accretionary structures and vertical motions that conflict with the forearc basal erosion model. Here we integrate such data to do an in‐situ accounting of material transfer at the plate boundary across the outermost 10 km of the forearc, characterized by active and inactive megathrusts. Our in‐situ budget finds an approximate balance between sediment recycling via accretion and underplating, 0.7–2.3 km³/km/m.y., and basal erosion, 0.7 km³/km/m.y., while subducting sediment volumes, 7.8 km³/km/m.y., greatly outpace either material transfer volumes. These budget results differ significantly from published estimates based on simple proxies of trench axis deflection and slope subsidence. These budget results are the summation of thin incoming hemipelagic sediments that variably accrete along the deformation front, underplating of hemipelagic sediments on the upthrown‐side and basal erosion on the downthrown‐side of active plate bending faulting landward of the trench axis, and sediment subduction primarily composed of pelagic sediments.

中文翻译：

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现场质量平衡估算哥斯达黎加近海

哥斯达黎加的会聚边缘被认为是一种侵蚀性边缘，侵蚀模型表明平均损失高达−153 km ³ / km / my。但是，三维（3D）地震反射和海洋钻探计划综合数据在奥萨半岛海上采集影像与前臂基底侵蚀模型相冲突的增生结构和垂直运动。在这里，我们整合这些数据，对前臂最外侧10 km处板块边界处的物质转移进行原位计算，其特征为活动和不活动的大推力。我们的现场预算发现，在通过吸积和垫层进行的沉积物再循环（0.7-2.3 km ³ / km / my）与基础侵蚀（0.7 km ^3）之间存在着近似的平衡/ km / my，但扣除沉积物体积7.8 km ³ / km / my时，大大超过了任何一种物质的输送量。这些预算结果与基于沟槽轴挠度和坡度沉降的简单近似值的已发布估算值明显不同。这些预算结果是沿变形锋线逐渐增加的稀薄的半海岸沉积物的总和，活动板弯曲的上向侧的半海岸沉积物的下沉和下侧的基底侵蚀的总和，从而使沟槽轴的断层向地面弯曲，沉积物俯冲主要由浮游沉积物组成。