Body-Wave Magnitude 1
Body-Wave Magnitude 1 : Earthquake magnitude calculated from amplitude/period ratios of body waves. mB and mb are based on data recorded by relatively broadband and short-period seismographs, respectively. The original body-wave magnitude introduced by B. Gutenberg (1945) and Gutenberg and Richter (1956) is denoted by m B. It has been determined by measuring the largest ratio of displacement amplitudes and periods of vertical and/or horizontal component P and PP waves as well as horizontal component S waves. Different from this, the more or less equivalent new IASPEI (2011) standard, denoted mB (BB) or mB_BB, is based only on direct measurement of the largest vertical component broadband velocity amplitude in the whole P-wave train (Bormann and Saul, 2008).Body-wave magnitudes assigned by USGS and ISC were up to 2011 only short-period mb (denoted Mb by the ISC), however, both agencies will in future additionally determine mB_BB. Also mb has been re-defined in a unique way (IASPEI 2005 and 2011) in order to avoid the sometimes significant differences between the mb values issued by different agencies. See: Chapter 3 and IS 3.3 in this Manual, Bormann et al. (2009) and Bormann (2011)
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