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51.
D.W.G. Arthur 《Icarus》1976,27(4):571-573
This note reviews the nature of the traditional (Mädler) lunar nomenclature and the recent developments based on the use of more than 2000 named provinces. It appears that the new nomenclature is less efficient than the old in many cases and may lead to an impossible publication situation. The unnecessary break with the past is especially critized. 相似文献
52.
Ian Main, Bruce Malamud, Chris Bean and John McCloskey summarize the presentations and lively debate at the British Geophysical Association's annual British Discussion Meeting on Scale-Invariance and Scale-Dependence in Earth Structure and Dynamics. 相似文献
53.
Arthur Rodgers Hrvoje Tkalcic David McCallen Shawn Larsen Catherine Snelson 《Pure and Applied Geophysics》2006,163(1):55-80
We report site response in Las Vegas Valley (LVV) from historical recordings of Nevada Test Site (NTS) nuclear explosions
and earthquake recordings from permanent and temporary seismic stations. Our data set significantly improves the spatial coverage
of LVV over previous studies, especially in the northern, deeper parts of the basin. Site response at stations in LVV was
measured for frequencies in the range 0.2–5.0 Hz using Standard Spectral Ratios (SSR) and Horizontal-Vertical Spectral Ratios
(HVR). For the SSR measurements we used a reference site (approximately NEHRP B ``rock' classification) located on Frenchman
Mountain outside the basin. Site response at sedimentary sites is variable in LVV with average amplifications approaching
a factor of 10 at some frequencies. We observed peaks in the site response curves at frequencies clustered near 0.6, 1.2 and
2.0 Hz, with some sites showing additional lower amplitude peaks at higher frequencies. The spatial pattern of site response
is strongly correlated with the reported depth to basement for frequencies between 0.2 and 3.0 Hz, although the frequency
of peak amplification does not show a similar correlation. For a few sites where we have geotechnical shear velocities, the
amplification shows a correlation with the average upper 30-meter shear velocities, V30. We performed two-dimensional finite difference simulations and reproduced the observed peak site amplifications at 0.6 and
1.2 Hz with a low velocity near-surface layer with shear velocities 600–750 m/s and a thickness of 100–200 m. These modeling
results indicate that the amplitude and frequencies of site response peaks in LVV are strongly controlled by shallow velocity
structure. 相似文献
54.
55.
Arthur H. Lachenbruch 《Pure and Applied Geophysics》1978,117(1-2):34-50
In regions of tectonic extension, vertical convective transport of heat in the lithosphere is inevitable. The resulting departure of lithosphere temperature and thickness from conduction-model estimates depends upon the mechanical mode of extension and upon how rapidly extension is (and has been) taking place. Present knowledge of these processes is insufficient to provide adequate constraints on thermal models. The high and variable regional heat flow and the intense local heat discharge at volcanic centers in the Basin and Range province of the United States could be accounted for by regional and local variations in extensional strain rate without invoking anomalous conductive heat flow from the asthenosphere. Anomalous surface heat flow typical of the province could be generated by distributed extension at average rates of about 1/2 to 1%/m.y., similar to rates estimated from structural evidence. To account for higher heat flow in subregions like the Battle mountain High, these rates would be increased by a factor of about 3, and locally at active bimodal volcanic centers, by an order of magnitude more. 相似文献
56.
Frank E. Senftle Arthur N. Thorpe Charles Briggs Corrine Alexander Jean Minkin David L. Griscom 《Earth and Planetary Science Letters》1975,26(3):377-386
The magnetic susceptibility of a terrestrial, synthetic and lunar ilmenite specimen has been measured from 4 to 300 K. All specimens had a single Néel temperature transition which ranged from 56 to 57.7 K. In one case the powdered specimen was partially aligned in the magnetic field prior to the susceptibility measurements and the Néel transition was observed to shift to 60 K indicating magnetic anisotropy. A study of several magnetic parameters calculated from the experimental data showed gross impurities in the terrestrial specimen, single-domain to multi-domain metallic iron in the synthetic specimen, and a small amount of superparamagnetic metallic iron in the lunar sample. No multidomain iron was observed in the lunar ilmenite. The results of electron spin resonance measurements were also in general agreement with these findings. Because of the absence of Fe3+ compared to most terrestrial samples it is suggested that the anisotropic magnetic parameters be determined on lunar ilmenite when a large enough single crystal becomes available. 相似文献
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60.
J.Arthur Snoke I.Selwyn Sacks Hiromu Okada 《Physics of the Earth and Planetary Interiors》1974,9(3):199-206
Various workers have constructed models to explain a class of anomalous arrivals at Peruvian and Chilean stations from deep-focus South American earthquakes. These arrivals are shear waves with a later arrival time, a higher frequency content, a longer duration and a lower apparent velocity than direct S. Our models assume that there is a sufficiently sharp discontinuity at the upper interface of the descending lithospheric slab between depths of 80 and 250 km to provide efficient reflection (≈0.1) for S-waves incident from below. The observed travel times require a single S-to-S reflection at this interface if the J-B velocity-depth model is modified to allow for 7% higher velocities down to a depth of 300 km (excluding the crust). The locus of required reflection points correlates well with the upper boundary of the observed seismicity (strike and dip angles within 5°) and Q for the proposed path is consistent with the frequency content of the anomalous arrivals. Thus the existence of these arrivals requires a dipping interface down to about 250 km, but, contrary to the wave-guide model of Isacks and Barazangi, cannot be used to infer a continuous lithospheric slab down to the deep-focus earthquakes (h #62; 500 km). 相似文献