Log-periodicity and Periodicity in Foreshocks and Aftershocks
Abstract
Log-periodicities observed in foreshock sequences may result from very precise fractal patterns of earthquake inter-event times (Virgin Islands; Varnes and Bufe, 1996), or may be artifacts of cumulative distributions in accelerating seismic release sequences (Loma Prieta; Huang et al., 2000). Foreshock sequences also manifest linear periodicity probably associated with triggering of earthquakes in situations of high stress or nearing criticality. Possible sources of such triggering are tidal and seasonal changes. Aftershocks of large earthquakes can exhibit periodicity due to triggering by free oscillations of the Earth (Bufe and Varnes, 2001). In both cases, triggering appears to occur preferentially for the larger events in the sequence. We discuss observations of annual, semi-annual, and fortnightly periods in precursory accelerating seismic energy release. These data indicate that conditions for triggering, and possibly criticality, may exist for decades before the occurrence of large earthquakes. In this paper we compare apparent log-periodicities in both the foreshocks and aftershocks of the 1997 M 7.8 Kamchatka earthquake and re-examine the periodicities and log-periodicities found in the Virgin Islands foreshock sequence, where the log-periodic intervals are multiples of fortnightly intervals.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFMNG41B..06V
- Keywords:
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- 7209 Earthquake dynamics and mechanics