The use of body-wave spectra in the determination of seismic-source parameters

abstract Teleseismic determinations of body-wave (P, S) spectra, interpreted in terms of the Brune (1970) seismic-source model, are used to estimate the parameters seismic moment (Mto) and source dimension (r) for three large, shallow, strike-slip earthquakes occurring on nearly vertical fault planes and for which the same parameters can be determined from field (F) data. These earthquakes are (1) the Borrego Mountain, California, earthquake (April 9, 1968) for which Mo(P) = 10, Mo(S) = 6.6, and Mo(F) = 3.6 × 1025 dyne-cm and r(p) = 14, r(S) = 23, and L/2(F) = 17 km; (2) the Mudurnu Valley, Turkey, earthquake (July 22, 1967) for which -Mo(P) = 9.1, Mo(S) = 8.5, and Mo(F) = 7.4 × 1026 dyne-cm, and r(P) = 39, r(S) = 48, and L/2(F) = 40 km; and (3) the Dasht-e-Bayāz, Iran, earthquake (August 31, 1968) for which Mo(P) = 4.8, Mo(S) = 8.6, and Mo(F) = 18 × 1026 dyne-cm, and r(P) = S1, r(S) = 48, and L/2(F) = 40 km. The Brune (1970) model is well-calibrated with respect to the determination of these parameters for the earthquakes considered. A minimum estimate for the radiated energy can be expressed in terms of Mo and r; this estimate is low by a factor of 10 with respect to the estimate obtained from energy-magnitude relations for these three earthquakes. The stress drops of these events are of the order of 10 bars.