Body Wave Magnitude (25 deg < D < 90 deg , T~1-3 s)

Calculation for the AS-1 Seismograph

Fig. (a) AmaSeis 24-hr record showing the Iceland Earthquake. Fig. (b) Extracted seismogram for the Iceland earthquake showing the P wave and the surface waves. Fig. (c) Close-up of the P-wave arrival. Click on the image for an enlarged view and an example of the measuring the amplitude and period.

Supply the first three inputs in the Calculator and click on <Calculate> to find the mb Magnitude.

EARTHQUAKE MAGNITUDE

Amplitude

Digital Units

from AS-1/AmaSeis

Distance

Degrees

Period

Seconds

Magnitude

mb

mb = log10(A/T) + 0.01*D + 5.9 (Compressional Body Wave (P-wave) Magnitude) defined by Gutenberg and Richter (1956) except that T, the period in seconds, is restricted to 1 to 3 s and A, the ground amplitude in micrometers, is not necessarily the maximum in the P group. D, the epicentral distance should be in the range 25° - 90°. Use only the following values of T : 1, 1.5, 2, 3, 5 seconds.

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

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