This study presents new seismic imaging of the Andean subduction zone through P-wave hybrid finite-frequency and ray-theoretical tomography. We measured both differential and absolute traveltimes using broadband seismic waveforms from stations in an array of ocean-bottom seismographs near the Chile Triple Junction (CTJ) and stations within 30° of the array. These data were combined with the global traveltime data set to obtain a global P-wave velocity structure with a focus on central to southern South America. The new tomographic image showed the Nazca slab geometry as a continuous fast anomaly, which is consistent with seismic activity and prior slab models. Furthermore, two notable structures were observed: a broad extension of the fast anomaly beneath the Nazca slab at 26–35°S and a slow anomaly east of the CTJ. The checkerboard resolution and recovery tests confirmed the reliability of these large-scale features. The fast anomaly, isolated from the Nazca slab, was interpreted as a relic Nazca slab segment based on its strong amplitude and spatial coincidence with the current Pampean and past Payenia flat slab segments. The slow anomaly near the CTJ was consistent with the previously inferred extent of the Patagonian slab window. Moreover, the active adakitic volcanoes are aligned with the southern edge of the anomaly, and the plateau basalts are located within the anomaly. Our model showed that the slow anomaly extended to a depth of up to 250 km, suggesting a depth limit that the asthenospheric window can influence.

中文翻译：

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通过有限频率层析成像拍摄的安第斯中部至南部俯冲带的地震图像


本研究通过 P 波混合有限频率和射线理论层析成像对安第斯俯冲带进行了新的地震成像。我们使用来自智利三重交界处 （CTJ） 附近海底地震仪阵列和阵列 30° 以内的站点的宽带地震波形测量了差分和绝对传播时间。这些数据与全球传播时间数据集相结合，获得了一个全球 P 波速度结构，重点是南美洲中部到南部。新的断层图像将 Nazca 板的几何形状显示为连续的快速异常，这与地震活动和之前的板模型一致。此外，还观察到两个值得注意的结构：南纬 26-35°的纳斯卡板块下方快速异常的广泛延伸和 CTJ 以东的缓慢异常。棋盘格分辨率和恢复测试证实了这些大规模特征的可靠性。从 Nazca 板中分离出来的快速异常被解释为遗迹 Nazca 板段，因为它与现在的 Pampean 和过去的 Payenia 平板段具有很强的振幅和空间重合。CTJ 附近的缓慢异常与先前推断的巴塔哥尼亚板窗范围一致。此外，活火山与异常的南部边缘对齐，高原玄武岩位于异常内。我们的模型显示，缓慢的异常延伸到高达 250 公里的深度，这表明软流圈窗口可以影响的深度限制。