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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS004 Oral Presentation 1896
Deglacial earthquakes in Fennoscandia can be reconciled with stablecraton-core
earthquake rates
Dr. John Adams
Geological Survey of Canada Geological Survey of Canada IASPEI
It is believed that the weight of the Greenland and Antarctic ice sheets inhibits current earthquake
activity (Johnston's 1987 hypothesis), and that when the Scandinavian ice sheet melted the stored
strain energy was released in a burst of large earthquakes in immediate deglacial times. I test the
hypothesis that, allowing for this effect, the long-term seismicity rate in Sweden is substantially the
same as that of other Stable Craton Cores (SCCs). I tried to reconcile the per-unit-area rate of
magnitude > 6 earthquakes from a) the low contemporary seismicity rate in Sweden, b) the high
seismicity rate that occurred immediately following deglaciation, and c) the much lower rate from the
past 8000 years (both b and c were taken from available paleoseismic catalogs) with the global SCC
rate. The reconciliation needs an assessment of the completeness of the information and some
additional assumptions. I conclude that the Swedish deglacial earthquakes appears to represent the
release of ~50,000 years strain accumulation at a typical stable craton seismic activity release rate. In
the long term, about 8 to 15 earthquakes of moment magnitude 6.0 or greater might be expected
within a 100-km radius of a site during a future 100,000 year period (the full uncertainty is much larger
than this best-estimate range). Past history indicates that much of this activity might be concentrated
into a relatively short time window in the more distant future, or alternatively the analysis places a limit
on the probability of a M>6 event in the near future.
Keywords: deglacial, earthquakes, sweden