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Seismic Image of the Central to Southern Andean Subduction Zone Through Finite-Frequency Tomography
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  • Yuko Kondo,
  • Masayuki Obayashi,
  • Hiroko Sugioka,
  • Hajime Shiobara,
  • Aki Ito,
  • Masanao Shinohara,
  • Hikaru Iwamori,
  • Masataka Kinoshita,
  • Matthew Miller,
  • Carlos Tassara,
  • Javier Ojeda
Yuko Kondo
Kobe University

Corresponding Author:[email protected]

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Masayuki Obayashi
Japan Agency for Marine-Earth Science and Technology
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Hiroko Sugioka
Kobe University
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Hajime Shiobara
University of Tokyo
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Aki Ito
Japan Agency for Marine-Earth Science and Technology
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Masanao Shinohara
University of Tokyo
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Hikaru Iwamori
The University of Tokyo
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Masataka Kinoshita
University of Tokyo
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Matthew Miller
Universidad de Concepción
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Carlos Tassara
Faculty of Science, Arturo Prat University
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Javier Ojeda
Departamento de Geofísica, Universidad de Chile
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Abstract

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° from the array. These data were combined with the global traveltime dataset 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.
02 Feb 2024Submitted to ESS Open Archive
02 Feb 2024Published in ESS Open Archive