Swarms of similar long-period earthquakes in the mantle beneath Mauna Loa Volcano     

Paul G. Okubo  Cecily J. Wolfe 《Journal of Volcanology and Geothermal Research》2008

We present analyses of two swarms of long-period (LP) earthquakes at > 30 km depth that accompanied the geodetically observed 2002–2005 Mauna Loa intrusion. The first LP earthquake swarm in 2002 consisted of 31 events that were precursory and preceded the start of Mauna Loa inflation; the second LP swarm of two thousand events occurred from 2004–2005. The rate of LP earthquakes slowed significantly coincident with the occurrence of the December 26, 2004 M_w 9.3 Sumatra earthquake, suggesting that the seismic waves from this great earthquake may have had a dynamic triggering effect on the behavior of Mauna Loa's deep magma system. Using waveform cross correlation and double difference relocation, we find that a large number of earthquakes in each swarm are weakly similar and can be classified into two families. The relocated hypocenters for each family collapse to compact point source regions almost directly beneath the Mauna Loa intrusion. We suggest that the observed waveform characteristics are compatible with each family being associated with the resonance of a single fluid filled vertical crack of fixed geometry, with differences in waveforms between events being produced by slight variations in the trigger mechanism. If these LP earthquakes are part of the primary magma system that fed the 2002–2005 intrusion, as indicated by the spatial and temporal associations between mantle seismicity and surface deformation, then our results raise the possibility that this magma system may be quite focused at these depths as opposed to being a diffuse network. It is likely that only a few locations of Mauna Loa's deep magma system met the geometric and fluid dynamic conditions for generating LP earthquakes that were large enough to be recorded at the surface, and that much of the deep magma transfer associated with the 2002–2005 intrusion occurred aseismically.  相似文献   

The whaling issue: [Marine Policy 2000;24(3):179–91]     

William Aron  William Burke  Milton M.R. Freeman 《Marine Policy》2000,24(6):501

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Determination of structure coefficients from splitting matrices     

Freeman Gilbert  & John H. Woodhouse 《Geophysical Journal International》2000,142(1):1-3

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High resolution absorption cross-section measurements of ozone at 195 K in the wavelength region 240–350 nm     

D.E. Freeman  K. Yoshino  J.R. Esmond  W.H. Parkinson 《Planetary and Space Science》1984,32(2):239-248

Cross-sections of the Hartley-Huggins bands of 03 at the temperature 195 K have been obtained from photoabsorption measurements at column densities in the range 2 × 10¹⁷?1 × 10²¹ cm^?2 throughout the wavelength region 240–350 nm with a 6.65 m photoelectric scanning spectrometer equipped with a 2400 lines mm^?1 grating and operated at an instrumental width (FWHM) of 0.003 nm. The assumptions made in putting the measured relative cross-sections on an absolute basis are discussed. Fine structure in the cross-section observed in the Huggins bands is illustrated in the region 323–327 nm where shallow features of width 0.01–0.02 nm occur superposed on a stronger apparent continuum exhibiting broader wavy structure.  相似文献   

Monitoring changes of ice streams using time series of satellite-altimetry-based digital terrain models     

Ute C. Herzfeld  Craig S. Lingle  Cecily Freeman  Chris A. Higginson  Michael P. Lambert  Li-Her Lee  Vera A. Voronina 《Mathematical Geology》1997,29(6):859-890

The Antarctic Ice Sheet plays a major role in the global system, and the large ice streams discharging into the circumpolar sea represent its gateways to the world’s oceans. Satellite radar altimeter data provide an opportunity for mapping surface elevation at kilometerresolution with meteraccuracy. Geostaristical methods have been developed for the analysis of these data. Applications to Seasat data and data from the Geosat Exact Repeat Mission indicate that the grounding line of Lambert Glacier/Amery Ice Shelf, the largest ice stream in East Antarctica, has advanced 10–12 km between 1978 and 1987–89. The objectives of this paper are to explore possibilities and limitations of satellite-altimetry-based mapping to capture changes for shorter time windows and for smaller areas, and to investigate some methodological aspects of the data analysis. We establish that one season of radar altimeter data is sufficient for constructing a map. This allows study of interannual variation and is the key for a limeseries analysis approach to study changes in ice streams. Maps of the lower Lambert Glacier and the entire Amery Ice Shelf are presented for austral winters 1978, 1987, 1988, and 1989. As a first step toward understanding the dynamics of the ice-stream/iceshelf system, elevation changes are calculated for grounded ice, the grounding zone, and floating ice. In the absence of (sufficient) surface gravity control for the Lambert Glacier/Amery Ice Shelf area, altimetry-based maps may facilitate improvement of geoid models as they provide constraints on the terrain correction in the inverse gravimetric problem.  相似文献   

Observably split multiplets—data analysis and interpretation in terms of large-scale aspherical structure     

Rudolf Widmer  Guy Masters  Freeman Gilbert 《Geophysical Journal International》1992,111(3):559-576

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Summary of conference     

David R. Criswell  John W. Freeman Jr. 《Earth, Moon, and Planets》1975,14(1):3-17

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Piltdown Man's ‘Treasure Map’          下载免费PDF全文

Eric F. Freeman 《Geology Today》2017,33(3):108-113

The ‘Maresfield Map’ is a map that purports to show features pertinent to the old iron industry in the Sussex Weald of southern England in 1724. It first appeared in a journal published by the Sussex Archaeological Society in early 1913, at roughly the same time as the formal publication by the Geological Society of London of papers introducing the discovery of the ‘remains’ of what became known as ‘Piltdown Man’ to the world. Piltdown Man was eventually revealed as fraudulent in 1953, followed by the Maresfield Map in 1974. Experiments in replication now show that the Maresfield Map is a sort of ‘treasure map’ (in a negative sense), which points fairly accurately to the supposed find‐spot of Piltdown Man, along with a coded accusation against Charles Dawson. The map's compiler is thought to have been L.F. Salzmann, the editor of the journal in which the map appeared. As such, the map represents the only such denunciation to have been published in the open literature in Dawson's lifetime, albeit a cryptic one. Mr Salzmann's possible motives are explored.  相似文献   

The Planetary Nebula Spectrograph elliptical galaxy survey: the dark matter in NGC 4494     

N. R. Napolitano †  A. J. Romanowsky  L. Coccato  M. Capaccioli †  N. G. Douglas  E. Noordermeer  O. Gerhard  M. Arnaboldi  F. De Lorenzi  K. Kuijken  M. R. Merrifield  E. O'Sullivan  A. Cortesi  P. Das  K. C. Freeman 《Monthly notices of the Royal Astronomical Society》2009,393(2):329-353

We present new Planetary Nebula Spectrograph observations of the ordinary elliptical galaxy NGC 4494, resulting in positions and velocities of 255 planetary nebulae out to seven effective radii (25 kpc). We also present new wide-field surface photometry from MMT/Megacam, and long-slit stellar kinematics from VLT/FORS2. The spatial and kinematical distributions of the planetary nebulae agree with the field stars in the region of overlap. The mean rotation is relatively low, with a possible kinematic axis twist outside  1 R _e  . The velocity dispersion profile declines with radius, though not very steeply, down to  ∼70 km s⁻¹  at the last data point.
We have constructed spherical dynamical models of the system, including Jeans analyses with multi-component Λ cold dark matter (CDM) motivated galaxies as well as logarithmic potentials. These models include special attention to orbital anisotropy, which we constrain using fourth-order velocity moments. Given several different sets of modelling methods and assumptions, we find consistent results for the mass profile within the radial range constrained by the data. Some dark matter (DM) is required by the data; our best-fitting solution has a radially anisotropic stellar halo, a plausible stellar mass-to-light ratio and a DM halo with an unexpectedly low central density. We find that this result does not substantially change with a flattened axisymmetric model.
Taken together with other results for galaxy halo masses, we find suggestions for a puzzling pattern wherein most intermediate-luminosity galaxies have very low concentration haloes, while some high-mass ellipticals have very high concentrations. We discuss some possible implications of these results for DM and galaxy formation.  相似文献   

The RAVE survey: constraining the local Galactic escape speed     

Martin C. Smith  Gregory R. Ruchti  Amina Helmi  Rosemary F. G. Wyse  J. P. Fulbright  K. C. Freeman  J. F. Navarro  G. M. Seabroke  M. Steinmetz  M. Williams  O. Bienaymé  J. Binney  J. Bland-Hawthorn  W. Dehnen  B. K. Gibson  G. Gilmore  E. K. Grebel  U. Munari  Q. A. Parker  R.-D. Scholz  A. Siebert  F. G. Watson  T. Zwitter 《Monthly notices of the Royal Astronomical Society》2007,379(2):755-772

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