Page 329 - Rock Mechanics For Underground Mining
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CHARACTERISATION OF SEISMIC EVENTS


                                          The magnitude and source mechanics of a seismic event can be conveniently rep-
                                        resented by a moment tensor. The moment tensor describes the magnitudes of the
                                        equivalent force singularities which simulates seismic point sources. It is made up of
                                        nine possible couples or dipole singularities, as illustrated in Figure 10.30. The mag-
                                        nitudes of the components of the moment tensor for a seismic event can be estimated
                                        from seismic records, but assumptions must be made about the properties of the rock
                                        mass. The properties and analysis of moment tensors are discussed in detail by Jost
                                        and Herrmann (1989).
                                          A commonly used model of seismic source mechanics is that due to Brune (1970,
                                        1971). This assumes a homogeneous stress drop over a circular section of a fault
                                        surface, of radius r 0 . The source radius is obtained from the corner frequency, f 0 ,
                                        identified in Figure 10.27 using the expression

                                                                                                    (10.103)
                                                                  r 0 = 2.34 C s /2 f 0



















































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