Export 2 results:
Sort by: Author Title Type [ Year  (Desc)]
Wolfe, CJ, Solomon SC, Laske G, Collins JA, Detrick RS, Orcutt JA, Bercovici D, Hauri EH.  2011.  Mantle P-wave velocity structure beneath the Hawaiian hotspot. Earth and Planetary Science Letters. 303:267-280.   10.1016/j.epsl.2011.01.004   AbstractWebsite

Three-dimensional images of P-wave velocity structure beneath the Hawaiian Islands, obtained from a network of seafloor and land seismometers, show an upper-mantle low-velocity anomaly that is elongated in the direction of the island chain and surrounded by a high-velocity anomaly in the shallow upper mantle that is parabolic in map view. Low velocities continue downward to the mantle tansition zone between 410 and 660 km depth and extend into the topmost lower mantle, although the resolution of lower mantle structure from this data set is limited. Comparisons of inversions with separate data sets at different frequencies suggest that contamination by water reverberations is not markedly biasing the P-wave imaging of mantle structure. Many aspects of the P-wave images are consistent with independent tomographic images of S-wave velocity in the region, but there are some differences in upper mantle structure between P-wave and S-wave velocities. Inversions without station terms show a southwestward shift in the location cif lowest P-wave velocities in the uppermost mantle relative to the pattern for shear waves, and inversions with station terms show differences between P-wave and S-wave velocity heterogeneity in the shallow upper mantle beneath and immediately east of the island of Hawaii. Nonetheless, the combined data sets are in general agreement with the hypothesis that the Hawaiian hotspot is the result of an upwelling, high-temperature plume. The broad upper-mantle low-velocity region beneath the Hawaiian Islands may reflect the diverging "pancake" at the top of the upwelling zone; the surrounding region of high velocities could represent a downwelling curtain; and the low-velocity anomalies southeast of Hawaii in the transition zone and topmost lower mantle are consistent with predictions of plume tilt. (C) 2011 Elsevier B.V. All rights reserved.

Tolstoy, M, Vernon FL, Orcutt JA, Wyatt FK.  2002.  Breathing of the seafloor: Tidal correlations of seismicity at Axial volcano. Geology. 30:503-506.   10.1130/0091-7613(2002)030<0503:botstc>;2   AbstractWebsite

Tidal effects on seafloor microearthquakes have been postulated, but the search has been hindered by a lack of continuous long-term data sets. Making this observation is further complicated by the need to distinguish between Earth and ocean tidal influences on the seafloor. In the summer of 1994, a small ocean-bottom seismograph array located 402 microseismic events, over a period of two months, on the summit caldera of Axial volcano on the Juan de Fuca Ridge. Harmonic tremor was also observed on all instruments, and Earth and ocean tides were recorded on tiltmeters installed within the seismometer packages. Microearthquakes show a strong correlation with tidal lows, suggesting that faulting is occurring preferentially when ocean loading is at a minimum. The harmonic tremor, interpreted as the movement of superheated fluid in cracks, also has a tidal periodicity.