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Bulletin of the Seismological Society of America, Vol. 93, No. 4, pp. 14331448, August 2003 Secondary Aftershocks and Their Importance for Aftershock Forecasting
 

Summary: 1433
Bulletin of the Seismological Society of America, Vol. 93, No. 4, pp. 1433­1448, August 2003
Secondary Aftershocks and Their Importance for Aftershock Forecasting
by Karen R. Felzer, Rachel E. Abercrombie, and Go¨ran Ekstro¨m
Abstract The potential locations of aftershocks, which can be large and damag-
ing, are often forecast by calculating where the mainshock increased stress. We find,
however, that the mainshock-induced stress field is often rapidly altered by after-
shock-induced stresses. We find that the percentage of aftershocks that are secondary
aftershocks, or aftershocks triggered by previous aftershocks, increases with time
after the mainshock. If we only consider aftershock sequences in which all after-
shocks are smaller than the mainshock, the percentage of aftershocks that are sec-
ondary also increases with mainshock magnitude. Using the California earthquake
catalog and Monte Carlo trials we estimate that on average more than 50% of after-
shocks produced 8 or more days after M 5 mainshocks, and more than 50% of all
aftershocks produced by M 7 mainshocks that have aftershock sequences lasting
at least 15 days, are triggered by previous aftershocks. These results suggest that
previous aftershock times and locations may be important predictors for new after-
shocks. We find that for four large aftershock sequences in California, an updated
forecast method using previous aftershock data (and neglecting mainshock-induced
stress changes) can outperform forecasts made by calculating the static Coulomb

  

Source: Abercrombie, Rachel E. - Department of Earth Sciences, Boston University

 

Collections: Geosciences