TY - JOUR

T1 - The 3-D Velocity Models and Seismicity Highlight Forearc Deformation Due to Subducting Features (Central Vanuatu)

AU - Foix, O.

AU - Crawford, W. C.

AU - Koulakov, I.

AU - Baillard, C.

AU - Régnier, M.

AU - Pelletier, B.

AU - Garaebiti, E.

PY - 2019/6/1

Y1 - 2019/6/1

N2 - The central Vanuatu forearc is characterized by a reduced convergence rate at the trench, significant uplift of the overriding plate, and the presence of large forearc islands. Volcanic activity and intermediate-depth seismicity behind the forearc are among the highest on Earth. These features are presumed to be associated with the subduction of a large seamount chain and an immersed ridge. We used a catalog of P and S arrivals from a local seismological network to construct the first 3-D velocity model of the region and to relocate earthquakes beneath the forearc. The 3-D model reveals a highly heterogeneous velocity distribution in the first 40 km beneath the surface. Trench-parallel low P and S velocity zones in the upper tens of kilometers beneath the western edges of the two largest forearc islands correlate to the major features entering into subduction and suggest highly fractured and probably water-infiltrated features. Trench-parallel high-velocity zones at 5–15-km depth, further to the east, may be part of a continuous consolidated rock structure that acts as a backstop. Thick overriding plate crust (29 ± 3 km) in the forearc is consistent with the presence of continental remnants. The earthquake distribution is generally heterogeneous, suggesting a complex fault structure and variable stress. Earthquakes are, however, well aligned at the plate interface in between the subducting features, where they constrain the angle of subduction to be 15° on average, down to 10–15-km depth.

AB - The central Vanuatu forearc is characterized by a reduced convergence rate at the trench, significant uplift of the overriding plate, and the presence of large forearc islands. Volcanic activity and intermediate-depth seismicity behind the forearc are among the highest on Earth. These features are presumed to be associated with the subduction of a large seamount chain and an immersed ridge. We used a catalog of P and S arrivals from a local seismological network to construct the first 3-D velocity model of the region and to relocate earthquakes beneath the forearc. The 3-D model reveals a highly heterogeneous velocity distribution in the first 40 km beneath the surface. Trench-parallel low P and S velocity zones in the upper tens of kilometers beneath the western edges of the two largest forearc islands correlate to the major features entering into subduction and suggest highly fractured and probably water-infiltrated features. Trench-parallel high-velocity zones at 5–15-km depth, further to the east, may be part of a continuous consolidated rock structure that acts as a backstop. Thick overriding plate crust (29 ± 3 km) in the forearc is consistent with the presence of continental remnants. The earthquake distribution is generally heterogeneous, suggesting a complex fault structure and variable stress. Earthquakes are, however, well aligned at the plate interface in between the subducting features, where they constrain the angle of subduction to be 15° on average, down to 10–15-km depth.

KW - earthquake locations

KW - forearc deformation

KW - New Hebrides

KW - passive tomography

KW - seismogenic zone

KW - subduction

KW - TECTONICS

KW - HEBRIDES-ISLAND-ARC

KW - GEODETIC MEASUREMENTS

KW - TOMOGRAPHIC INVERSION

KW - SEISMOTECTONICS

KW - DENTRECASTEAUX ZONE

KW - CONVERGENCE

KW - COLLISION ZONE

KW - BENEATH

KW - EMERGED CORALS

UR - http://www.scopus.com/inward/record.url?scp=85067413462&partnerID=8YFLogxK

U2 - 10.1029/2018JB016861

DO - 10.1029/2018JB016861

M3 - Article

AN - SCOPUS:85067413462

VL - 124

SP - 5754

EP - 5769

JO - Journal of Geophysical Research: Solid Earth

JF - Journal of Geophysical Research: Solid Earth

SN - 2169-9313

IS - 6

ER -