1887
Volume 22, Issue 9
  • ISSN: 0263-5046
  • E-ISSN: 1365-2397

Abstract

John R. Stowell, president, Mount Sopris Instrument Company, Colorado reports on the near surface geophysics elements of the EarthScope project in the US, set up to study the structure, evolution and dynamics of the North American continent. The historical record is filled with striking reminders that the ‘terra firma’ upon which we live is far from firm. From the ancient eruptions at Pompeii to more contemporary events at Krakatoa, San Francisco, Mount St. Helens, and Kobe, an observer can easily assume that our earth’s near surface is a dynamic system. In the late 18th Century, Hutton and others startled the scientific (and theological) communities by proposing a completely new model of planet Earth. Based on observations and evidence on several continents, ideas about the age and composition of the subsurface took a dramatic turn. Over the next century, support of these radical propositions grew and became generally accepted by the scientific community. And in the last 30 years, Hess and others have applied global and extra-terrestrial observations in support of the general theory of plate tectonics. Not only was the earth an extremely old orb of layered material, but its crust was in constant, if extremely slow deformation. Oceans’ ridges were extruding new material while continent-sized plates were grinding old rock back down into the earth’s interior. Catastrophes like Mount St. Helens and Kobe have shown that sudden changes in the ‘near surface’ can cause serious economic and environmental consequences. So it is not surprising that national and international political bodies have asked the global scientific community for help in minimizing the effects of such activity. In Japan and the US, several programmes have been funded to meet this challenge. In the US, the National Science Foundation (NSF) is responsible for a programme called EarthScope. NSF is an independent agency of the US government established by the National Science Foundation Act of 1950. The mission of EarthScope is to apply modern observational, analytical and telecommunications technologies to investigate the structure and evolution of the North American continent and the physical processes controlling earthquakes and volcanic eruptions. EarthScope includes a multi-purpose array of instruments and observatories that will greatly expand the observational capabilities of the earth sciences and permit better understanding of the structure, evolution and dynamics of the North American continent. Two components of EarthScope deal with near-surface geophysics. One, called the San Andreas Fault Observatory at Depth (SAFOD) is well under way. SAFOD (Fig. 1) is designed to directly sample fault zone materials (rock and fluids), measure a wide variety of fault zone properties, and monitor a creeping and seismically active fault zone at depth. A 3.2 km deep hole will be drilled through the San Andreas fault zone close to the hypocentre of the 1966 M~6 Parkfield earthquake, where the San Andreas fault slips through a combination of small-to-moderate magnitude earthquakes and a seismic creep. As of early August, drilling had reached ~1450 m where 13 3/8 in casing had been set in preparation for the next drilling phase. At a depth of approximately 3 km, the hole will be kicked off in an attempt to drill through the fault system.

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/content/journals/0.3997/1365-2397.22.9.26013
2004-09-01
2024-03-28
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  • Article Type: Research Article
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