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2009-04-06 – SEMINAR by Shane Murphy: Estimating an earthquake’s magnitude using initial P- and S-arrivals

6 April, 2009 (16:00 GMT), 5 Merrion Square, Dublin 2.

Speaker: Shane Murphy (University College Dublin).
Title: Estimating an earthquake’s magnitude using initial P- and S-arrivals.


Recent seismological analysis has shown a general scaling between final magnitude and the averaged first few seconds of ground motion recorded by seismic arrays.
This scaling is now being used in earthquake early warning systems to estimate the size of an occurring earthquake. However the cause of this scaling is not clearly understood nor is the range over which it is applicable known. One possible explanation for this scaling is that an earthquake’s final size is somehow related to it’s initiation.  Another possible hypothesis is that the initial recorded ground motion relates to a substantial section of the overall fault size.

By using simple dynamic and kinematic numerical models we investigate both theories.  Our dynamic models show that scaling is valid only over a narrow magnitude range for a particular class of rupture. Simple kinematic models on the other hand provide a more fruitful result whereby scaling between magnitude and a simplified peak ground displacement is similar to that observed in real data.