Ms_20 is the surface wave magnitude measured on the vertical component at around 20 s period in accordance with the IASPEI standards.



The Ms_20 amplitudes are calculated on vertical-component displacement seismograms corrected for the instrument response of a WWSSN_LP seismograph.

Station Magnitude

Ms_20 is the surface-wave magnitude at 20 s period based on the recommendations by the IASPEI magnitude working group issued on 27 March, 2013.

M_s = \log \left(\frac{A}{T}\right) + 1.66 \log(\Delta) + 0.3


A: WWSSN_LP corrected ground displacement in nm measured on the vertical-component seismogram as the maximum absolute trace amplitude of a surface wave at periods between 18 s and 22 s,

T: period of the surface wave in seconds.

The term Ms_20 is chosen in accordance with the IASPEI standard as of 2013. Alternatively, the term Ms(20) may be used.

Network magnitude

By default, the trimmed mean is calculated from the station magnitudes to form the network magnitude. Outliers below the 12.5% and above the 12.5% percentiles are removed before the calculation.


Adjust the configurable parameters in global bindings in the Ms_20 section.