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Development of Improved Magnitude Measures for the International Data Centre

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Conference paper

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Many of the most important issues in nuclear test monitoring at the International Data Centre IDC, such as event screening, depend critically on the details of the definitions of the various magnitude measures to be employed by the IDC and their relations to the classical National Earthquake Information Center, International Seismological Centre, and Air Force Technical Application Center magnitude measures, which have historically been used to assess seismic verification capability. Therefore, it is important that these IDC magnitude measures be well understood and carefully calibrated. During the past year, we have been continuing to refine the IDC mb and MS magnitude measures and have initiated an effort to implement an automated Lg-based magnitude measure for application to small, continental seismic events. The effort on mb has been directed toward incorporation of PKP observations into the generalized mb determination. A GLM statistical analysis has now been performed on the large sample of PKP amplitude measurements determined from the PIDC IMS station observations to obtain new distance corrections applicable over the PKP distance range. The resulting distance corrections have been compared both with those currently being employed at the IDC and with those previously derived by Lilwall 1987 and some significant differences have been noted. Moreover, the estimated uncertainties in these derived epicentral distance correction factors for PKP have been found to be comparable to or smaller than those previously estimated for the normal teleseismic P distance range. Thus it appears that incorporation of PKP data, will significantly reduce the nominal uncertainties in the network-averaged generalized mb values for at least some events. Current effort on this task is directed toward the evaluation of the applicability of the previously derived teleseismic P-wave station corrections to PKP observations at those same stations.

Subject Categories:

  • Seismology
  • Statistics and Probability
  • Seismic Detection and Detectors

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