Abstract. The objective of this work is to analyse the density structure of the continental forearc in the northern segment of the 1960 Mw 9.6 Valdivia earthquake. Regional 2D and local 3D density models have been obtained from available gravity data in the area, complemented with new gravimetric stations. Models are constrained by independent geophysical/geological information and new TEM and MT soundings. The results show a segmentation of the continental wedge along and perpendicular to the margin, highlighting a high density anomaly, below the onshore forearc basin, that limits the Late Paleozoic-Early Mesozoic metamorphic basement in the region where Chaitenia terrain has been proposed. A progressive landward shift of this anomaly correlates with the high slip patch of the giant 1960 Mw 9.6 Valdivia earthquake. Based on these results, we propose that the horizontal extension of the less rigid basement units conforming the marine wedge and Coastal Cordillera domain could modify the process of stress loading during the interseismic periods, and also that changes in position and extension of the Late Paleozoic-Early Mesozoic accretionary complex could be linked with the frictional properties of the interplate boundary. This analysis provides new evidence of the role of the overriding plate structure on the seismotectonic process in subduction zones.

中文翻译：

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1960年瓦尔迪维亚大地震北部上覆板块弧前密度结构

摘要。这项工作的目的是分析 1960 年 Mw 9.6 瓦尔迪维亚地震北段大陆前弧的密度结构。区域 2D 和局部 3D 密度模型已从该地区可用的重力数据中获得，并辅以新的重力站。模型受到独立的地球物理/地质信息和新的 TEM 和 MT 探测的约束。结果显示大陆楔沿和垂直于边缘的分割，突出了陆上弧前盆地下方的高密度异常，限制了已提出 Chaitenia 地形的地区的晚古生代-早中生代变质基底。这种异常逐渐向陆地移动与 1960 Mw 9.6 Valdivia 大地震的高滑动斑块相关。基于这些结果，我们提出，符合海楔和沿海山脉域的刚性较低的基底单元的水平延伸可以改变震间期应力加载过程，并且晚古生代-早中生代增生杂岩的位置和伸展的变化可以与板间边界的摩擦特性有关。这一分析为上覆板块结构对俯冲带地震构造过程的作用提供了新的证据。此外，晚古生代-早中生代增生杂岩位置和伸展的变化可能与板间边界的摩擦性质有关。这一分析为上覆板块结构对俯冲带地震构造过程的作用提供了新的证据。此外，晚古生代-早中生代增生杂岩位置和伸展的变化可能与板间边界的摩擦性质有关。这一分析为上覆板块结构对俯冲带地震构造过程的作用提供了新的证据。