Accomplishments - IRIS

Mantle Shear-Wave Velocity Structure beneath the Hawaiian
Hotspot
Cecily Wolfe (University of Hawaii at Manoa), Sean Solomon (Carnegie Institution of Washington), Gavi Laske (Scripps
Institution of Oceanography), Robert S. Detrick (Woods Hole Oceanographic Institution), John A. Orcutt (Scripps
Institution of Oceanography), David Bercovici (Yale University), Erik H. Hauri (Carnegie Institution of Washington)
Hawaii is the archetypal hotspot and has been suggested to be the
surface expression of a mantle plume, a localized upwelling of hot buoyant
material from Earth’s deep mantle, although such an origin has been
debated. One of the most straightforward indications of whether a hotspot
is the result of a plume is the presence of a narrow, vertically continuous
zone of low seismic velocities in the underlying mantle, indicative
of higher-than-normal temperatures, anomalous mantle composition,
or partial melt. Defining the mantle structure that lies beneath hotspots
such as Hawaii is thus important for revealing the origin of such features.
The Hawaiian Plume-Lithosphere Undersea Melt Experiment (PLUME)
was a multidisciplinary program whose centerpiece was a large network
of four-component broadband ocean-bottom seismometers and threecomponent
portable broadband land stations [Laske et al., 2009]. Data
from IRIS Global Seismic Network stations KIP and POHA were used
in this study, and all of the collected data were archived at the IRIS Data
Management Center.
Three-dimensional images of shear-wave velocity beneath the
Hawaiian Islands obtained from the PLUME records show an uppermantle
low-velocity anomaly that is elongated in the direction of the
island chain and surrounded by a high-velocity anomaly that is parabola-shaped
in map view [Wolfe et al., 2009]. Low velocities continue
downward to the mantle transition zone between 410 and 660 kilometers
depth, a result that is in agreement with prior observations of transition-zone
thinning at this location. The inclusion of SKS observations
extends the imaging resolution downward to a depth of 1500 kilometers
and reveals a several-hundred-kilometer-wide region of low velocities
beneath and southeast of Hawaii. These images support the hypothesis
that the Hawaiian hotspot is the result of an upwelling high-temperature
plume from the lower mantle.
Top plot: Upper mantle shear-wave velocity heterogeneity at 200
km depth. Station locations are indicated by squares. The scale
is given at the upper right and ranges ±3%. Bottom plot: Vertical
cross section. The scale ranges over ±1%.
References
Laske, G., J. A. Collins, C. J. Wolfe, S. C. Solomon, R. S. Detrick, J. A. Orcutt, D. Bercovici, and E. H. Hauri, Probing the Hawaiian hotspot with
new broadband ocean bottom instruments, Eos Trans. AGU, 90, 362-363, 2009.
Wolfe, C. J., S. C. Solomon, G. Laske, J. A. Collins, R. S. Detrick, J. A. Orcutt, D. Bercovici, and E. H. Hauri, Mantle shear-wave velocity structure
beneath the Hawaiian hotspot, Science, 326, 1388-1390, 2009.
Acknowledgements: This project was supported by the U.S. National Science Foundation. We also acknowledge the crews of the research vessels
Melville, Ka’imikai-O-Kanaloa, and Kilo Moana, the Jason remotely operated vehicle team, the Ocean Bottom Seismograph Instrument
Pool, the Carnegie Institution’s portable seismology laboratory, IRIS, and the hosts of temporary stations on the Hawaiian Islands.
IRIS Core Proposal 2010 | Volume II | Upper Mantle Structure and Dynamics | II-221