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Seismic velocity structure of the slab and continental plate in the region of the 1960 Valdivia (Chile) slip maximum — Insights into fluid release and plate coupling

Dzierma, Yvonne ; Rabbel, Wolfgang ; Thorwart, Martin ; Koulakov, Ivan ; Wehrmann, Heidi ; Hoernle, Kaj ; Comte, Diana

Earth and planetary science letters, 2012-05, Vol.331-332, p.164-176 [Periódico revisado por pares]

Elsevier B.V

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  • Título:
    Seismic velocity structure of the slab and continental plate in the region of the 1960 Valdivia (Chile) slip maximum — Insights into fluid release and plate coupling
  • Autor: Dzierma, Yvonne ; Rabbel, Wolfgang ; Thorwart, Martin ; Koulakov, Ivan ; Wehrmann, Heidi ; Hoernle, Kaj ; Comte, Diana
  • Assuntos: Anomalies ; Fluid dynamics ; Fluid flow ; Fluids ; Fracture mechanics ; Global Positioning System ; local earthquake tomography ; plate coupling ; Seismic phenomena ; seismology ; south-central Chile ; subduction zones ; Valdivia Fracture Zone ; Volcanoes
  • É parte de: Earth and planetary science letters, 2012-05, Vol.331-332, p.164-176
  • Notas: ObjectType-Article-2
    SourceType-Scholarly Journals-1
    ObjectType-Feature-1
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  • Descrição: The south-central Chilean subduction zone has witnessed some of the largest earthquakes in history, making this region particularly important for understanding plate coupling. Here we present the results of a local earthquake tomography study from a temporary local seismic network in the Villarrica region between 39 and 40°S, where the largest coseismic displacement of the 1960 Valdivia earthquake occurred. A low-velocity anomaly and high Vp/Vs values occur under the coastal region, indicating mantle serpentinisation and/or underthrusting of forearc material. Further east, a high-velocity anomaly is observed, interpreted as “normal” high-velocity mantle. Under the active volcanic arc a low-velocity anomaly together with high Vp/Vs ratios (1.8 and higher) likely images fluid ascent beneath the volcanoes. Close to the subducting Valdivia Fracture Zone, the coastal low-velocity anomaly extends further inland, where it interrupts and shifts the high-velocity anomalies associated with “normal” fast mantle velocities. This may indicate enhanced fluid presence along this part of the margin, probably caused by a stronger hydration of the incoming plate along the Valdivia Fracture Zone. This is consistent with geochemical fluid proxies (U/Th, Pb/Ce, Ba/Nb) in young volcanic rocks displaying peak values along the volcanic front at Llaima and Villarrica Volcanoes, and with recent GPS measurements, which suggested a local reduction in plate coupling in this region. The shift in the high-velocity anomaly underlying the central part may be caused by a north to south decrease in plate age and hydration across the Valdivia Fracture Zone, and may explain why a Central Valley is absent in this segment of the margin. The low La/Yb ratios in the volcanic rocks from Villarrica and Llaima suggest that the high slab-derived fluid flux causes elevated degrees of melting beneath these volcanoes, providing an explanation as to why these are amongst the most active volcanoes in South America. ► Local earthquake tomography near 1960 Valdivia slip maximum (39–40°S), Chile. ► Typical subduction zone velocity structure interrupted along Valdivia Fracture Zone. ► Along the subducting VFZ, low mantle velocities and high Vp/Vs indicate fluid release. ► Agrees with geochemical fluid tracers in magmas of Villarrica and Llaima volcanoes. ► This may cause a local low in plate coupling.
  • Editor: Elsevier B.V
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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