abstract

The examination of the BENHAM aftershocks is extended to 162 earthquakes approximately an order of magnitude smaller than those previously studied. The spatial distribution of these smaller events is similar to that found for larger events examined by Hamilton and Healy (1969). Focal mechanisms are also similar to those of the larger aftershocks: dip-slip along northeasterly trending zones and generally strike-slip along a north-south trending zone west of the shot-point. About one third of the mechanism solutions are ambiguous, capable of either interpretation. Amplitude data are successfully used to resolve the ambiguity in about one half of these cases by selecting the solution which gives a notably lesser value of the variance, Σ ((Ai, obs − kAi, calc)2/N of the amplitude residuals. The value of k is related to the magnitude of the shocks. A b value of 1.09 indicates that aftershocks of the explosion follow a recurrence rate normal for regional earthquakes or aftershock sequences.

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