Surface Wave Magnitude (20 deg < D < 160
deg, T~20 s)
Calculation for the AS-1 Seismograph
Fig. (a) AmaSeis
24-hr record of the August 4, 2000, MS 7.1 Sakhalin Island
earthquake. Fig. (b) Extracted seismogram of the Sakhalin Island earthquake showing the P arrival
and the surface wave arrivals. Fig. (c) Close-up of
the surface wave arrivals. Click on the image for an enlarged view and an
example of measuring the amplitude and period.
Supply the first three inputs in the Calculator
and click on <Calculate> to find the MS Magnitude.
Ms = log (A/T) + 1.66 log D + 3.3 where A is the maximum
ground amplitude in micrometers (microns) of the vertical component of the
surface wave within the period range 18 to 22 s. T is the period in seconds.
Use T=20s for the calculator. D is the distance in geocentric degrees (station
to epicenter) and 20° <= D <= 160°.
by Lawrence W. Braile & Saptarshi
Dasgupta, Purdue University, May, 2003
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main AS-1 magnitude calculator page