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Seismic Wave Propagation in South America,

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The Comprehensive Test Ban Treaty, at present being negotiated in the Conference on Disarmament, requires an International Seismic Monitoring System and On-Site Inspections. Harjes has recalled three lessons learned from previous Group of Scientific Experts Technical Tests 1 The International Seismic Monitoring System needs to be calibrated with respect to standard travel time curves and amplitude-distance relations. 2 Provision of adequate surface wave detection and reporting should be included in the design of the International Seismic Monitoring System. 3 To detect and locate small events, the observation of the seismic wavefield at regional distances is essential. On-Site Inspection requires the location of events, whether earthquakes or explosions, to plus or minus 5 km. In the highly irregular region of northern and western South America, we cannot simply use uncorrected partial derivatives from standard travel-time curves. We have found the response curves of the seismographs that operated at La Paz from the years 1913 to 1962, thus revealing a considerable amount about South American seismicity. We have observed at La Paz that Lg waves of periods of 1.5 and 1.6 s arrive from the Caribbean Sea, north of northwestern Colombia, but not from the Chilean trench to the west of La Paz. We have constructed models of the structure below Iquique, Chile, and of structure below the oceanic trench off the coast from Iquique. For the model of the structure below the oceanic trench of f the coast of Iquique, the modes of the shorter periods travel practically entirely in the sediments in the trench assumed to be of thickness 1 km, while the mode of period 10 is travels predominantly in the low velocity zone at a depth of approximately 110 km.

Subject Categories:

  • Government and Political Science
  • Seismology
  • Seismic Detection and Detectors
  • Nuclear Weapons

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