Definition
The formula to calculate surface wave magnitude is:
where A is the maximum particle displacement in surface waves (vector sum of the two horizontal displacements) in μm, T is the corresponding period in s, Δ is the epicentral distance in °, and
According to GB 17740-1999, the two horizontal displacements must be measured at the same time or within 1/8 of a period; if the two displacements have different periods, weighed sum must be used:
where AN is the north-south displacement in μm, AE is the east-west displacement in μm, TN is the period corresponding to AN in s, and TE is the period corresponding to AE in s.
Read more about this topic: Surface Wave Magnitude
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