Publications
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Assessment of models proposed for the 1985 revision of the international geomagnetic reference field
Geomagnetic measurements from land, marine and aerial surveys conducted in the years 1945-1964 were used to test the 14 models proposed as additions, for that period, to the series of definitive geomagnetic reference field (DGRF) models. Overall, NASA's 'SFAS' models and the BGS (British Geological Survey) models agree best with these data. Comparisons of the two proposed definitive main-field mod
Authors
N. W. Peddie, A. K. Zunde
The geomagnetic jerk of 1969 and the DGRFs
Cubic spline fits to the DGRF/IGRF series indicate agreement with other analyses showing the 1969-1970 magnetic jerk in the h ??12 and g ??02 secular change coefficients, and agreement that the h ??11 term showed no sharp change. The variation of the g ??01 term is out of phase with other analyses indicating a likely error in its representation in the 1965-1975 interval. We recommend that future d
Authors
D. Thompson, J.C. Cain
A model of geomagnetic secular variation for 1980-1983
We developed an updated model of the secular variation of the main geomagnetic field during 1980 through 1983 based on annual mean values for that interval from 148 worldwide magnetic observatories. The model consists of a series of 80 spherical harmonics, up to and including those of degree and order 8. We used it to form a proposal for the 1985 revision of the International Geomagnetic Reference
Authors
N. W. Peddie, A. K. Zunde
On the interpretation of the geomagnetic energy spectrum
Two recent high-degree magnetic energy spectra, based mostly on MAGSAT data, are compared and found to agree very well out to order and degree n = 15, but the spectrum remains somewhat uncertain for higher degrees. The hypothesis that a primary break in the slope of the spectrum, plotted semi-logarithmically, is due to a transition from dominance by core sources to dominance by crustal magnetizati
Authors
E.R. Benton, L.R. Alldredge
Rainfall, ground-water flow, and seasonal movement at Minor Creek landslide, northwestern California: Physical interpretation of empirical relations
Simple ground-water flow analyses can clarify complex empirical relations between rainfall and landslide motion. Here we present detailed data on rainfall, ground-water flow, and repetitive seasonal motion that occurred from 1982 to 1985 at Minor Creek landslide in northwestern California, and we interpret these data in the context of physically based theories. We find that landslide motion is clo
Authors
R. M. Iverson, J. J. Major
On regional geomagnetic charts
When regional geomagnetic charts for areas roughly the size of the United States were compiled by hand, some large local anomalies were displayed in the isomagnetic lines. Since the late nineteen sixties, when the compilation of charts using computers and mathematical models was started, most of the details available in the hand drawn regional charts have been lost. One exception to this is the Ca
Authors
L.R. Alldredge
Valles Marineris, Mars: Wet debris flows and ground ice
Detailed study of the Valles Marineris equatorial troughs suggests that the landslides in that area contained water and probably were gigantic wet debris flows: one landslide complex generated a channel that has several bends and extends for 250 km. Further support for water or ice in debris masses includes rounded flow lobes and transport of some slide masses in the direction of the local topogra
Authors
Baerbel K. Lucchitta
Recent mafic volcanism on Mars
The evidence for volcanism on Mars is commonly accepted, but none has been documented in the Valles Marineris equatorial rift system. A recent survey of the troughs in this valley revealed dark patches that are interpreted to be volcanic vents. The configuration and association of these patches with tectonic structures suggest that they are of internal origin; their albedo and color ratios indicat
Authors
Baerbel K. Lucchitta
Current loops fitted to geomagnetic model spherical harmonic coefficients.
One hundred-sixty circular current loops with radial axes were fitted by least squares to the 899 spherical harmonic coefficients of a 29th degree model. In the first case, the parameters that were fitted for each loop were the normalized magnetic moment, the distance from the center of the Earth to the current element, the colatitude and E. longitude of the loop axis, and one-half of the central
Authors
L.R. Alldredge
On predicting changes in the geomagnetic field
The present method of using constant secular variation rates to forecast magnetic components at a given site or to forecast spherical harmonic coefficients is known to be inaccurate. A new predictive method using trend and trigonometric functions fitted to known past values is used to extrapolate for a few years into the future. This provides an improvement over the usual linear extrapolation meth
Authors
L.R. Alldredge
Reflections from midcrustal rocks within the Mesozoic subduction complex near the eastern Aleutian Trench
Seismic reflection data collected in 1973 by Western Geophysical Company show that highly reflective rocks make up the midcrust of the convergent margin adjacent to the eastern Aleutian Trench. These rocks form an arch that strikes obliquely across the strongly expressed northeast-southwest structural grain of exposed Mesozoic rocks. In an earlier report we proposed that the deep events mark the l
Authors
M. A. Fisher, Roland E. von Huene, G.L. Smith
The crustal structure of the axis of the Great Valley, California, from seismic refraction measurements
In 1982 the U.S. Geological Survey collected six seismic refraction profiles in the Great Valley of California: three axial profiles with a maximum shot-to-receiver offset of 160 km, and three shorter profiles perpendicular to the valley axis. This paper presents the results of two-dimensional raytracing and synthetic seismogram modeling of the central axial profile. The crust of the central Great
Authors
W.S. Holbrook, Walter D. Mooney