Magnitude studies from ultra-long-period records

Summary. Records from the ultra-long-period seismometer at UCLA were used for finding magnitude formulas valid at longer periods, longer distances and greater depths of focus than the formulas used routinely. For Rayleigh waves from shallow focus events M = log( A/T )+ 1.66–0.9 log(T/20)] logΔ+ 13.3 +0.65 +2.9 log(T/20)] was found to be consistent with the data over a wide range of periods and distances. The same formula, with only a small change, was found to be applicable also for deep focus events, down to a depth of over 600 km. A preliminary formula for long-period body-wave magnitudes was found as well.