Articles by Peter Smith

PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. Silt layers in lake sediments up to 2,300 years old have been interpreted as the result of earthquakes that caused landslides on tributary streams and the resuspension of sediment. If this view is valid, the recurrence interval of large earthquakes in eastern North America must have been very variable--120 years between 300 B.C. and 800 A.D., and 75 years from 1500 A.D. to the present. The prospect of estimating se

Department of Earth Sciences Open University Milton Keynes, U.K. The great mystery of the 1985 Mexican earthquake is that, whereas 371 modern high-rise buildings collapsed, thousands of colonial masonry structures (many with tall steeples) in the same area remained standing. This puzzle may be solved. Theoretical calculations suggest that ultrashort surface waves (gravity waves) may have liquified the area's sediments to a shallow depth that would have included the foundations of modern buil

The Scientist has asked a group of experts to comment periodically upon recent articles that they have found noteworthy. Their selections, presented here in every issue, are neither endorsements of content nor the result of systematic searching. Rather, the list represents personal choices of articles the columnists believe the scientific community as a whole may also find interesting. Reprints of any articles cited here may be ordered through The Genuine Article, 3501 Market St., Philadelphia,

The Scientist has asked a group of experts to comment periodically upon recent articles that they have found noteworthy. Their selections, presented here in every issue, are neither endorsements of content nor the result of systematic searching. Rather, the list represents personal choices of articles the columnists believe the scientific community as a whole may also find interesting. Reprints of any articles cited here may be ordered through The Genuine Article, 3501 Market St., Philadelphia,

Author: PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. The Cleopatra structure on Venus, 100 kilometers in diameter, has the morphology of an impact crater but the distinctly different depth-diameter ratio of a volcanic crater. It is not yet possible to decide whether it is a very strange impact crater or a very strange volcanic crater. A.T. Basilevsky, B.A. Ivanov, "Cleopatra crater on Venus: Venera 15/16 data and impact/volcanic origin controversy," Geophys

GEOSCIENCES BY PETER J. SMITH Departmentof Earth Sciences Open University Milton Keynes, U.K. " Even as the final parts (south China and Cimmeria) were coming together to complete the construction of Pangea, the supercontinent was undergoing incipient rifting (leading to breakup) in eastern North America, in northwest and east Africa, and here. There was a major turning point 230 million years ago, when because of the first major loss of heat from the reservoir beneath Pangea there was a cha

GEOSCIENCES BY PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. " On 1 August 1986, a seismic disturbance occurred near the Novaya Zemlya, USSR, nuclear test sites at a time when the Soviet Union claimed to be observing a unilateral moratorium on nuclear testing. This caused some concern, because the area is relatively aseismic. Regional seismic data failed to answer the obvious question, but teleseismic data now show that the disturbance was indeed an earthquak

GEOSCIENCES BY PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. " To avoid the semantic confusion inherent in the use of the term “catastrophe” to describe mass extinctions, a scale has been devised to express the magnitude of such rare events. By partial analogy with the Richter earthquake-magnitude scale, extinction magnitude (Me) is defined as the natural logarithm of the ratio of accelerated extinction rate to background extinction rate over a

GEOSCIENCES BY PETER J. SMITH Department of Earth Science Open University Milton Keynes, U.K. " New seismic data from Australia combined with earlier world data indicate that, depending on the precise assumptions made about the earth’s outer liquid core, the solid inner core has an ellipticity of 1.9 x 10^-3 to 5.6 x 10^-3 . This corresponds to a polar flattening of 1.6 to 5.0 km. A. Souriau, M. Souriau, “Ellipticity and density at the inner core boundary from subcritical PKiKP a

GEOSCIENCES BY PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. " A new earthquake magnitude scale (Mm) based on the spectral amplitude of very-long-period Rayleigh waves can be determined from a single station and with no knowledge of focal mechanism or depth. Unlike classical magnitude scales, it bears a clear relationship to seismic movement—Mg—and is immune to interference saturation. EA. Okal, J. Talandier, “Mm: A variable-period mantle m

GEOSCIENCE BY PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. " Data from isotopes and incompatible elements show that the Kolar Schist Belt in southern India’s Dharwar Craton is a suture zone marking the accretion of distinct terrains during the Archean. Plate-tectonic processes were thus shaping the Earth’s crust as early as 2500 million years ago. EJ. Krogstad, S. Balakrishnan, D.K. Mukhopadhyay, V. Rajamani, G.N. Hanson, “Plate tectonics

GEOSCIENCES BY PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. " A new type of carbonate-platform margin has been recognized in the Gulf of Mexico and Caribbean regions. Named a “scalloped margin,” it comprises a series of irregular embayments, convex on the platform side, and is thought to be largely an erosional feature produced by large-scale failure triggered by earthquakes or resulting from undercutting by dissolution. H.T. Mullins, A.C. Hin

GEOSCIENCES BY PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. " A recent redetermination of solar composition showed that the Sun’s Fe abundance is 40% higher than previously thought and that Fe/Si and Ca/Al atomic ratios are 30% to 40% higher than chrondritic values. These new data require a fundamental re-evaluation of the. composition of the Earth’s mantle, which is likely to be chemically layered. The lower mantle, in particular, must be much r

GEOSCIENCES BY PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. " A recent redetermination of solar composition showed that the Sun’s Fe abundance is 40% higher than previously thought and that Fe/Si and Ca/A1 atomic ratios are 30% to 40% higher than chrondritic values. These new data require a fundamental re-evaluation of the composition of the Earth’s mantle, which is likely to be chemically layered. The lower mantle, in particular, must be much r

GEOSCIENCES BY PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. " Seismic reflection studies in the North Atlantic, southwest of Bermuda, show that the oceanic crust is not as uniform as hitherto supposed. In particular, dipping reflectors in the lower crust indicate either major fault zones or, more probably, chemical signatures of magma chambers once active on the mid-Atlantic ridge, note the authors of a new study. J. McCarthy, J.C. Mutter, J.L. Morton, N.H.