Use of long-period surface waves for rapid determination of earthquake source parameters 2. Preliminary determination of source mechanisms of large earthquakes (M_S ⩾ 6.5) in 1980

Abstract

An inversion method for fast retrieval of earthquake source parameters developed earlier has been applied to 28 large (M_S ⩾ 6.5), shallow earthquakes which occurred in 1980. Rayleigh waves recorded by the IDA (International Deployment of Accelerographs) network were used for the analysis. For very shallow events, the inversion is ill-conditioned and two of the moment-tensor elements, M_(zx) and M_(zy), are unresolvable. Of the 28 events, a solution is obtained for 25 with the constraints M_(zx) = M_(zy) = 0. Although these constraints limit the solution to be either vertical strike-slip or 45° dip-slip, the method provides a useful first approximation to the mechanism solution. For deeper events, all of the elements of the moment tensor can be determined. After the seismograms have been retrieved, the solution can be obtained in ∼10 min for most events. The method would be adequate for preliminary cataloging purposes.

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