Download Volume II Accomplisments (28 Mb pdf). - IRIS

Rayleigh Waves Observed During the Hawaiian Plume Deployment
Trace Anomalously Low Shear Velocities in the Lithosphere and
Asthenosphere
G. Laske (UC San Diego), J.A. Orcutt (UC San Diego), J.A. Collins (Woods Hole Oceanographic Institution), C.J. Wolfe
(University of Hawaii at Manoa), S.C. Solomon (Carnegie Institution of Washington), R.S. Detrick (Woods Hole
Oceanographic Institution), D. Bercovici (Yale University)
Hawaii has long been viewed as the textbook example of a plume-fed hotspot although other models such as a progressively
cracking lithospheric plate have been considered to explain Hawaii's island chain. The plume model has been heavily contested
by some as it has been difficult to obtain comprehensive and unambiguous geophysical observational constraints. One major
problem that seismology has faced has been its complete reliance on land stations. During two field campaigns from 2005 to
2007, the Plume-Lithosphere-Undersea-Mantle Experiment (PLUME) occupied 83 sites to provide continuous year-long seismic
records [Laske et al., 2009]. Nearly 70 of these sites were occupied by ocean bottom seismometers (OBSs), most of which
featured a broadband seismometer (a Guralp CMG-3T or a Nanometrics Trillium 240). To date, we have compiled two-station
Rayleigh wave phase velocity curves for over 600 paths across the 1000-km-wide network, and we have use these curves in
inversions for 3-dimensional (3-D) shear velocity structure. Our 3-D images in the lithosphere and asthenosphere reveal a pronounced
low velocity anomaly to the west of the island of Hawaii at depths of 80 km and greater. Toward shallower depths, the
anomaly appears to diminish in size and magnitude and is centered between the islands of Hawaii and Maui. We interpret this
anomaly as the likely source of melt that feeds Hawaii’s extensive volcanism.
References
Laske, G., J. A. Collins, C. J. Wolfe, S. C. Solomon, R. S. Detrick, J. A. Orcutt, D. Bercovici, and E.H. Hauri (2009), Probing the Hawaiian hotspot
with new broadband ocean bottom instruments, Eos Trans. AGU, 90, 362-363.
Vs Perturbations from N&F 52-100 Ma
Lithosphere and Asthenosphere
Nishimura, C.E. and D.W. Forsyth, (1989), The anisotropic structure of the upper mantle in the Pacific. Geophys. J., 96, 203-229.
Acknowledgements: The waveforms from this experiment are available at the IRIS-DMC. This research was financed by the National Science
Foundation under grants OCE-00-02470 and OCE-00-02819.
Vs=4.59km/s
26 26
Vs=4.23km/s
60 km 120 km
26 26
24 24
24 24
22 22
22 22
20 20
20 20
18 18
18 18
16 16
16 16
14 14 14 14
-162 -160 -158 -156 -154 -152 -150 -162 -160 -158 -156 -154 -152 -150
dV/Vs [%]
-4 -3 -2 -1 0 1 2 3 4
Model of shear velocity anomalies obtained from inverting Rayleigh wave phase velocity curves. The maps show percentage perturbations to reference velocities for
52-100 Ma old oceanic lithosphere (Nishimura and Forsyth, 1989).
II-222 | 2010 IRIS Core Programs Proposal | Volume II | Upper Mantle Structure and Dynamics