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.

EARTHQUAKE MAGNITUDE

Amplitude

Digital Units

from AS-1/AmaSeis

Distance

Degrees

Period

Seconds

Magnitude

MS

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°.

Developed by Lawrence W. Braile & Saptarshi Dasgupta, Purdue University, May, 2003

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