Abstract

A survey of the continuing microearthquake activity in the 1982 Miramichi earthquake epicentral region of central New Brunswick took place between July 3 and August 19, 1985. MEQ-800 analog seismographs were deployed at six recording stations for the 47 day period of the survey. Three BakPak digital seismographs were added to the network on July 23, two at the same locations as analog units and one at a seventh site.Three hundred and twenty-five microearthquakes were recorded during the survey. The activity was episodic, with days of few earthquakes being followed by periods when events clustered together in miniswarms. Coda-magnitude relationships for five stations were established from regression analysis of scaled coda lengths of events on the MEQ 800 records and Nuttli magnitudes determined at an Eastern Canadian Telemetered Network station KLN. Only 21 of the events had coda magnitudes (Mc) greater than 0, the largest being 2.0. The larger magnitude earthquakes occurred in zones where there had been little preceding activity. The highest rate of activity was associated with the northeastern corner of the 1982 aftershock zone. Sporadic activity was also recorded from the western side of the zone.Composite P-nodal solutions for three subzones are consistent with the conjugate pattern of thrust faulting obtained in previous studies, except for rotation of fault-plane strikes from northerly to northwesterly directions for two of the subzones. It is remarkable that the pattern of activity first mapped by the 1982 aftershock surveys has remained relatively stationary over the subsequent 3½ year period.Un levé microséismique de l'activité courante dans la région épicentrale du tremblement de terre de Miramichi au Nouveau-Brunswick de janvier 1982 a été effectué entre le 3 juillet et le 19 août 1985. Des séismographes portatifs (MEQ 800) furent installés à six stations pendant une période de 47 jours. Trois séismographes numériques (BakPak) furent ajoutés au réseau le 23 juillet : deux sur sites de MEQ 800's et l'autre sur un septième emplacement.

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