Magnitude determinations from coda duration of underground nuclear explosions.

The concept of determining magnitudes, M_Tau, of regional events (DELTA less than 1000 km) by means of coda-duration measurements is reexamined by using short-period vertical- component seismogram from Nevada Test Site explosions. The duration is specified as the time interval between the expected arrival of the S-wave and the time when coda waves fall and stay below 80 millimicrons peak-to-peak ground displacement. The suggested procedure requires that for M_Tau equals 4.0 the coda duration at a distance of 100 km is 120 seconds. The adaptivity of the method is examined in terms of the single-station magnitude scatter, and with respect to the potential accuracy of theyield simation of the explosions. The derival magnitude formula for underground nuclear explosions in granite is of the form M_Tau equals 0.18 + 0.001DELTA + 1.79 log Tau + C_s, where C_s is a station correction oefficient for non-WWNS stations-Author