Long-Period Seismological Research Program

Abstract

In the past 6 months, research has concentrated on the development and application of a surface-wave magnitude scale based on the amplitude of higher-mode Rayleigh waves. A relatively high ratio of higher mode to fundamental mode energy can be produced when an unusual combination of source depth and focal mechanism leads to poor excitation of the fundamental mode Rayleigh wave, in which case, the amplitude of the higher mode yields a more reliable estimate of the size of the event than the amplitude of the fundamental mode. Several anomalous events in central Asia, which are characterized by unusually low M(s):m(b) ratios and hence could be suspected to be nuclear explosions, are reclassified as earthquakes when the new, higher-mode scale, M(s)h, is employed. The focal depth and mechanism of these anomalous events apparently causes poor excitation of the fundamental mode Rayleigh wave without significantly affecting the amplitude of the higher mode. Elimination of these source related factors from traditional M(s):m(b) discriminants is an essential tool for reliable discrimination between earthquakes and nuclear underground tests.

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Document Details

Document Type
Technical Report
Publication Date
Dec 31, 1975
Accession Number
ADA108522

Entities

People

  • Donald W. Forsyth
  • Lynn R. Sykes
  • William J. Best

Organizations

  • Lamont–Doherty Earth Observatory

Tags

Communities of Interest

  • Energy and Power Technologies
  • Materials and Manufacturing Processes

DTIC Thesaurus Topics

  • Amplitude
  • Asia
  • Central Asia
  • Contracts
  • Data Analysis
  • Discrimination
  • Earthquakes
  • Excitation
  • Explosions
  • Frequency
  • High Gain
  • Nuclear Explosions
  • Rayleigh Waves
  • Recording Systems
  • Surface Waves
  • Underground Explosions
  • Waves

Readers

  • Atmospheric Science / Meteorology, specifically Wind Wave Turbulence.
  • Seismology