Background seismicity

The assumption that areas of lower natural seismicity also are areas less likely to respond with high levels of induced seismicity, or with lower maximum magnitudes is intuitive. Evans et al. (2012) suggested, based on a European database, that indeed areas with lower background hazards (defined arbitrarily as peak ground acceleration (PGA) values < 0.08) also have lower maximum observed magnitudes. To investigate this potentially important relation further, we have updated the Evans et al. (2012) database, adding data from outside of Europe. As seen in Figure 114, these additional data suggest that the hypothesis of low PGA regions producing lower maximum magnitude events can be rejected.