Determination of seismic moment and related source parameters of shallow local earthquakes from Wellington records

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Gibowicz, S.J. 1975 Determination of seismic moment and related source parameters of shallow local earthquakes from Wellington records. [s.l.]: [s.n.]. Report / Geophysics Division 99 32 p.

Abstract: Simple but sufficiently accurate methods are needed for routine determination of the seismic moment and source dimension of local earthquakes. These specify other source characteristics: average displacement, stress drop and seismic energy. The seismic moment of shallow earthquakes can be calculated from the long-period parameter AR, which measures the excitation of surface waves as recorded by standard Press-Ewing seismographs. The details of a simple routine method of estimating AR are given. The source dimension, usually expressed as the radius of an equivalent circular fault surface, can be estimated from the difference between the logarithm of seismic moment and local magnitude ML, which is itself a spectral parameter of the source. This estimate can be made for earthquakes with source radii greater than about 0.5 km. This restriction is of practical concern for micro- earthquakes but not for larger events. Appropriate formulae are stated, and diagrams and tables to facilitate routine calculation are given. A list giving these parameters for 346 New Zealand earthquakes, for the most part obtained by the methods described, is included, together with a brief discussion of their regional variations in space and local variations in time. (auth.)