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During the recent period of relative seismic quiescence along the Parkfield segment of the San Andreas fault (late 1986-late 1988), the average magnitude of earthquakes was lower than usual. Throughout 1989, however, it was back to normal. This pattern has been observed before other mainshocks and, by comparison, suggests that the mainshock expected at Parkfield should occur "in the near future." M. Wyss, "Changes of mean magnitude of Parkfield seismicity: a part of the precursory process?" Ge

The Scientist Staff

During the recent period of relative seismic quiescence along the Parkfield segment of the San Andreas fault (late 1986-late 1988), the average magnitude of earthquakes was lower than usual. Throughout 1989, however, it was back to normal. This pattern has been observed before other mainshocks and, by comparison, suggests that the mainshock expected at Parkfield should occur "in the near future."

M. Wyss, "Changes of mean magnitude of Parkfield seismicity: a part of the precursory process?" Geophysical Research Letters, 17, 2429-32, December 1990. (University of Colorado, Boulder)

Simple ("Ediacaran") fauna have been found at about 25 sites around the world, in all cases above the tillites of the Varanger glacial epoch. However, simple biogenic annuli and discs have now been discovered in Canada below the uppermost glacial layer. These not only are probably the oldest metazoan fossils yet found, but also throw doubt on the hypothesis that the evolution of...

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