- Calculate distance and azimuth to BDSN stations ans also the appropriate time window that spans the required Rayleigh waves.
- Determine when sufficient time has elapsed since the origin time for the Rayleigh wave to propagate to the BDSN stations then extract the BK.LHZ data.
- Bandpass filter (6PBP @ 17-23 sec) each trace and deconvolve to ground displacement.
- For each trace, determine the maximum trace amplitude (A) in microns and the corresponding period (T) in seconds.
- Calculate
*M*_{s}for each BDSN station using the Prague formula: . - Calculate median and interquartile range. With
20 BDSN broadband stations, the median and interquartile range provide the most robust estimate of
*M*_{s}and its uncertainty.

*bdsn_ms 1999.229,00:01 40.702 29.987 17. *

The *bdsn_ms* results for the major earthquake that occurred in Turkey on August 18, 1999 are given in Table 27.2. The file name is: 199908170001.Ms. The resulting BDSN *M*_{s} estimate of 7.87
0.088 is compatable with the NEIC *M*_{s} estimate of 7.8.

During the past five years, 673 teleseisms occurred which had *M*_{s} determined independently by both the NEIC and BDSN. Empirically, we have found that the BDSN estimates are most robust when data from at least 14 BDSN stations are used for determining *M*_{s}. The resulting *M*_{s} estimates are compared in Figure 27.1. The standard error between the two estimates is 0.17. The differences between the two estimates is primarily attributed to the fact that the aperture spanned by the BDSN stations is generally much smaller than the aperture spanned by stations used by the NEIC. The median interquartile range for the 14+ station BDSN estimates is 0.073.

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