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Event Location and Characterisation,

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The accurate location and subsequent characterisation of seismic events is a primary requirement of any verification regime for a test ban treaty. Such procedures depend on the use of good models for the propagation of seismic waves and also accurate picks for identified seismic phases. An improved radial model of Earth structure has been developed, model ak135 which provides a very good fit to the empirical travel times for a wide range of seismic phases. The improvements in fit to S phases and core phases compared with tasp91 or sp6 should improve the accuracy of location procedures exploiting later phases. This representation of the major contribution to teleseismic arrivals needs to be supplemented by correction procedures to allow for the main sources of lateral heterogeneity within the Earth. Ellipticity corrections have been developed for the ak135 model for a very wide range of phases. A regionalised model for upper mantle corrections is under development as part of a hierarchical scheme of corrections to allow for different influences on the travel times of a wide range of seismic phases. Precision location requires a good representation of the Earth and also accurate and correctly identified time picks for seismic phases. We have been developing automatic phase detection and recognition procedures which can help with the association of seismic arrivals for use in the location procedures. A pattern recognition approach has allowed the extraction of phase wavelets whose character can be recognised through the interaction of a number of energy measures applied to three component waveforms. Subsequent activity will be directed to try to improve the estimation of the depth of seismic events by integrating knowledge of waveform characteristics with estimation of source character.

Subject Categories:

  • Government and Political Science
  • Seismology
  • Seismic Detection and Detectors
  • Nuclear Weapons
  • Geology, Geochemistry and Mineralogy

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