Seismic hazard – sensitivity to b-value

Probabilistic seismic hazard calculations are dependent on the number of events (N) and the b-value. But which has more effect on the hazard result? The chart below shows how seismic hazard varies with b-value for N = 1,000, N = 10,000 and N = 100,000.

The seismic hazard in the chart below can be considered in the following way. For a given time span and volume, if N events have been recorded, what is the probability that one of those events was above Mdesign? In this case Mdesign = ML2.

Seismic hazard increases with increasing N and decreasing b-value. Note on the chart, N = 1,000 and b = 0.9 gives the same seismic hazard as N = 10,000 and b = 1.2 (approx.). In other words an increase of 0.3 in b means you need 10 times more events for an equivalent hazard.

So, seismic hazard is very sensitive to the b-value of the area. This is important to consider when looking at daily activity rates. In some areas, 100 events may represent a very different hazard to 100 events in another area if the b-value varies.

Another point of interest in the chart is that for areas with b-values above 2, even very high event numbers represent low hazard.

For assistance with any of these features, you are always welcome to reach out to the mXrap team at moc.parxmobfsctd-68b99f@troppus