3-D Seismic Velocity Structure of the Hawaii Hotspot from Joint Inversion of Body Wave and Surface Wave data
Abstract
The Hawaii hotspot and the associated chain of islands have been long regarded as the case example of a deep-rooted mantle plume. However the efforts to detect a thermal plume seismically have been inconclusive. In this study we combine the complementary sensitivities of body- and surface-waves in order to improve resolution of mantle structure beneath Hawaii. Adding surface-wave constraints to the body wave inversion improves the resolution of the crustal and upper mantle structure. We used data from the deployment of temporary broadband ocean-bottom seismometers (OBS) of the Hawaiian Plume-Lithosphere Undersea Melt Experiment (PLUME) together with data from the on-shore stations in order to make the most complete dataset available. In a first step, we obtained stable and reliable OBS orientations over a range of earthquake back-azimuths using teleseismic P-wave particle motions. Due to the high noise of the OBS data in some frequency bands, we began by filtering in the period band of 0.04-1Hz. Using the proper channel orientations, we measured ~800 S-wave relative arrival times (direct S and SKS phases) on the SV component using muti-channel cross correlation. We applied the two-plane wave tomography method to generate surface wave phase velocity information. We use surface waves from 71 events with magnitude greater than 5.8 to generate phase velocity maps from 25 sec to 100 sec. These maps clearly show the low velocities beneath the islands surrounded by relatively high phase velocity. The pure S wave inversion result shows the 3-D structure beneath the PLUME array to a depth of 1000km and reveals a several-hundred-kilometer-wide region of low velocities beneath Hawaii that dips to the southeast. The low velocities continue downward through the mantle transition zone and extend into the uppermost lower-mantle where our resolution begins to degrade. These images are consistent with the interpretation that the Hawaiian hotspot is the result of an upwelling high-temperature plume from the lower mantle. The broader upper-mantle low-velocity region immediately beneath the Hawaiian Islands likely reflects the horizontal spreading of the plume material beneath the lithosphere. We also obtain result from the joint body-wave and surface-wave inversion. The same shallow low velocity zone is imaged along the island chain and the deeper part is identical to the body-wave inversion image. The low velocity to the southwest of the island is also clear to a depth of 600km. However, this low velocity limb is relatively small compared to the one from the southeast. This suggests this southwest limb is the result of spreading and interaction of the plume with the lithosphere. If the observation here is true, it will provide a hot environment for the 660km discontinuity to the west of the Hawaii and may give a new perspective to the plume origin debate.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMDI53A2355C
- Keywords:
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- 7270 SEISMOLOGY / Tomography