Surface-wave magnitude

The surface wave magnitude (
 
 
 
 
 M
 
 s
 
 
 
 
 {\displaystyle M_{s}}
 
) scale is one of the <a href="/facts/Seismic_scale/g5uSHyQe">magnitude scales</a> used in <a href="/facts/Seismology/Lony1LYX">seismology</a> to describe the size of an <a href="/facts/Earthquake/NGjIzagw">earthquake</a>. It is based on measurements of <a href="/facts/Rayleigh_wave/QAlu9lQo">Rayleigh surface waves</a> that travel along the uppermost layers of the Earth. This magnitude scale is related to the <a href="/facts/Local_magnitude_scale/UDhqkAX1">local magnitude scale</a> proposed by <a href="/facts/Charles_Francis_Richter/rLoXEJSt">Charles Francis Richter</a> in 1935, with modifications from both Richter and <a href="/facts/Beno_Gutenberg/jTJqBeNs">Beno Gutenberg</a> throughout the 1940s and 1950s. It is currently used in People's Republic of <a href="/facts/China/lTjIXY5p">China</a> as a <a href="/facts/Guobiao/bUH1ggRa">national standard</a> (GB 17740-1999) for categorising earthquakes.

The successful development of the local-magnitude scale encouraged <a href="/facts/Beno_Gutenberg/jTJqBeNs">Gutenberg</a> and <a href="/facts/Charles_Richter/rLoXEJSt">Richter</a> to develop magnitude scales based on teleseismic observations of earthquakes. Two scales were developed, one based on surface waves, 
 
 
 
 
 M
 
 s
 
 
 
 
 {\displaystyle M_{s}}
 
, and one on body waves, 
 
 
 
 
 M
 
 b
 
 
 
 
 {\displaystyle M_{b}}
 
.
Surface waves with a period near 20 s generally produce the largest amplitudes on a standard long-period seismograph, and so the amplitude of these waves is used to determine 
 
 
 
 
 M
 
 s
 
 
 
 
 {\displaystyle M_{s}}
 
, using an equation similar to that used for 
 
 
 
 
 M
 
 L
 
 
 
 
 {\displaystyle M_{L}}
 
.— William L. Ellsworth, The San Andreas Fault System, California (USGS Professional Paper 1515), 1990–1991
Recorded magnitudes of earthquakes through the mid 20th century, commonly <a href="/facts/Richter_magnitude_scale/UDhqkAX1">attributed to Richter</a>, could be either 
 
 
 
 
 M
 
 s
 
 
 
 
 {\displaystyle M_{s}}
 
 or 
 
 
 
 
 M
 
 L
 
 
 
 
 {\displaystyle M_{L}}
 
.

Surface-wave magnitude open-in-new

Surface-wave magnitude