Publication Date:
2018-07-10
Description:
The structure and seismicity of the subduction zone of centralCosta Rica have been investigated
with local earthquake tomography down to ca. 50 km depth. Seismic traveltime data sets of
three on- and offshore seismic networks were combined for a simultaneous inversion of
hypocentre locations, 3-D structure of P-wave velocity and Vp/Vs ratio using about 2000 highquality
events. The seismicity and slab geometry as well as Vp and Vp/Vs show significant
lateral variation along the subduction zone corresponding to the changes of the incoming plate
which consists of serpentinized oceanic lithosphere in the northwest, a seamount province
in the centre and the subducting Cocos Ridge in the southeast of the investigation area.
Three prominent features can be identified in the Vp and Vp/Vs tomograms: a high-velocity
zone with a perturbation of 4–10 per cent representing the subducting slab, a low-velocity
zone (10–20 per cent) in the forearc crust probably caused by deformation, fluid release and
hydration and a low-velocity zone below the volcanic arc related to upwelling fluids and
magma. Unlike previously suggested, the dip of the subducting slab does not decrease to the
south. Instead, an average steepening of the plate interface from 30◦ to 45◦ is observed from
north to south and a transition from a plane to a step-shaped plate interface. This is connected
with a change in the deformation style of the overriding plate where roughly planar, partly
conjugated, clusters of seismicity of regionally varying dip are observed. It can be shown that
the central Costa Rica Deformation Belt represents a deep crustal transition zone extending
from the surface down to 40 km depth. This transition zone indicates the lateral termination
of the active part of the volcanic chain and seems to be related to the changing structure of the
incoming plate as well.
Type:
Article
,
PeerReviewed
Format:
text
DOI:
10.1111/j.1365-246X.2010.04717.x
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