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No. 111: May-Jun 1997

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Exotic Seismic Signals

Not all terrestrial tremors emanate from buckling crust and slipping tectonic plates. The crashing of large waves on a seashore sends "microseisms" to sensitive instruments hundreds of kilometers away. The bubblings of Old Faithful geyser give rise to an enduring and engaging "harmonic tremor."

As for the more "exotic" sources of seismic signals, they had an entire session devoted to them at the Fall 1996 meeting of the American Geophysical Union. Here are two of the unusual seismic events presented there.

July 10, 1996. Yosemite National Park.

"At 6:52 pm PDT Wednesday, July 10, 1996, a large block of granite, with an estimated mass of 80,000 to 184,000 tons, detached from the cliff between Washburn Point and Glacier Point, in Yosemite Valley. The rock mass subsequently launched from the cliff and free-fell ballistically an estimated 550 m before impacting approximately 30 meters from the base of the cliff in the Happy Isles area of the valley floor in Yosemite National Park...This rock fall was well recorded by 3 UC Berkeley (BDSN) and Caltech (TERRAscope) broadband seismographic stations and 15 shortperiod seismographic stations (operated by the USGS in Menlo Park and the University of Nevada, Reno). In fact, it is the largest vertical rock free-fall ever recorded seismically and it registered on seismographs up to 200 km distant."

(Uhrhammer, R.A.; "Seismic Analysis of the Yosemite Rock Fall of July 10, 1996," Eos, 77:508, 1996.)

December 9, 1995. Southern Ecuador.

"On the afternoon of December 9, 1995, a bolide exploded in the atmosphere over the Andes in southern Ecuador. Many people in nearby towns witnessed the event. They reported seeing a streaking meteor, which terminated in a loud and brilliant explosion. In some locales, the flash was noticeable even through cloud cover. The burst of light was observed by satellite optical sensors used to detect atmospheric nuclear tests. Three local seismic stations also recorded signals from the explosion...This bolide appears to be unique in that it was observed by eyewitnesses and located by both satellite and ground-based sensors."

The sound of the meteor's explosion was heard at least 56 kilometers away.

(Chael, Eric P.; "Seismic Signals from a Bolide in Ecuador," Eos, 77:508, 1996.)

From Science Frontiers #111, MAY-JUN 1997. 1997-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:

Quotes

  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987