Abstract
Hawaii is one of the best-known examples of hotspot volcanism in the
world. The insulated position in the central Pacific keeps away additional
tectonic effects. Hence, in the context of mantle plumes Hawaii is
a site of special interest. Until now neither the depth of the plume
source nor the exact position of its conduit in the mantle are well-known.
Answers to these questions may also bring new cognition linked to
the dynamical processes of the mantle such as convection. Within
this work the receiver function technique has been applied to image
seimic velocity structures down to the uppermost part of the lower
mantle beneath Hawaii. Data from eleven temporary broadband seismic
stations located on the four biggest Hawaiian islands have been investigated.
Supplementary data have been available from permanent broadband stations.
A couple of observations have been made in different depths. Moho
depths between 12 - 17 km have been derived. Underneath the younger
part of the island chain from the Big Island to Oahu an additional
converted phase beeing generated within the crust. To the younger
part it is occuring systematically earlier in the seismic section.
The lithosphere-asthenosphere boundary was clearly observed in the
area under investigation. The thickness of the lithosphere is decreasing
to the older part of the island chain. Within the asthenosphere a
local low velocity zone has been verified underneath the Big Island.
The discontinuities of the mantle transition zone in 410 km and 660
km depth have also been identified. In some parts also converted
phases generated at 520 km and also greater depths have been found.
According to arrival times of the P410s and P660s phases the area
could have been devided into three regions: The southeast does not
show any influences of a mantle plume at all, while in the northwestern
part reduced S-wave velocities in the uppermost mantle are found.
Southwest of the Big Island, finally, thinning of the mantle transition
zone indicates the position of the plume conduit in this depths with
a core radius of about 120 km. urn:nbn:de:kobv:188-2004001722
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