.. _global_ms_20: ##### Ms_20 ##### Surface wave magnitude measured at around 20 s Description =========== Ms_20 is the surface wave magnitude measured on the vertical component at around 20 s period in accordance with the IASPEI standards. Amplitude --------- The Ms_20 amplitudes are calculated on vertical-component displacement seismograms corrected for the instrument response of a :term:`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 (:cite:t:`iaspei-2013`). .. math:: M_s = \log \left(\frac{A}{T}\right) + 1.66 \log(\Delta) + 0.3 with A: :term:`WWSSN_LP` corrected ground displacement in units of 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 (:cite:t:`iaspei-2013`). Alternatively, the term *Ms(20)* may be used. * Amplitude unit in |scname|: **nanometer** (nm) * Time window: 0 s - distance (km) / 3.5 km/s + 30 s * Period range: 18 s - 22 s, configurable: :confval:`magnitudes.Ms_20.lowerPeriod`, :confval:`magnitudes.Ms_20.upperPeriod` * Default distance range: 20 - 160 deg, configurable: :confval:`magnitudes.Ms_20.minDist`, :confval:`magnitudes.Ms_20.maxDist` * Depth range: <= 100 km, configurable: :confval:`magnitudes.Ms_20.maxDepth` Network magnitude ----------------- By default, the trimmed mean is calculated from the station magnitudes to form the :term:`network magnitude`. Outliers below the 12.5% and above the 12.5% percentiles are removed before the calculation. Configuration ------------- Adjust the configurable parameters in global bindings in the Ms_20 section. Add Ms_20 to the list of computed amplitudes and magnitudes in the configuration of :ref:`scamp` and :ref:`scmag` and in :ref:`scesv` or :ref:`scolv` for visibility.