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BDSN Surface Wave Magnitude Calculation

Robert A. Uhrhammer

Introduction

A new algorithm, bdsn_ms, has been developed to expedite the calculation of surface wave magnitude Ms from BDSN vertical component broadband recordings. The algorithm was developed to aid the duty seismologist in the rapid calculation of Ms for significant earthquakes.


  
Table 27.1: bdsn_ms command line parameters.
\begin{table}
\begin{center}
\epsfig{file=bob00_4_1.eps, width=7cm}\end{center}\end{table}

Description

In order to facilitate the timely calculation of Ms a new algorithm, bdsn_ms, was developed which automates the calculation of Ms once the location of seismic source is known. The processing steps in the algorithm are:

Sample Input and Output

The command line arguments for bdsn_ms are given in Table 27.1and the command invoked to calculate Ms for the major earthquake that occurred in Turkey on August 18, 1999 is:

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 Ms estimate of 7.87 $\pm$0.088 is compatable with the NEIC Ms estimate of 7.8.


  
Table 27.2: Sample bdsn_ms output.
\begin{table}
\begin{center}
\epsfig{file=bob00_4_2.eps, width=7cm}\end{center}\end{table}

Comparison of NEIC Ms and BDSN Ms Estimates

During the past five years, 673 teleseisms occurred which had Ms 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 Ms. The resulting Ms estimates are compared in Figure 27.1. The standard error between the two estimates is $\pm$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 $\pm$0.073.


  
Figure 27.1: Comparison of NEIC and BDSN Ms Estimates. The dashed line has a slope of one.
\begin{figure}
\begin{center}
\epsfig{file=bob00_4_3.eps, width=7cm}\end{center}\end{figure}


next up previous contents
Next: New Constraints on the Up: Ongoing Research Projects Previous: Advances in InSAR Techniques

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