New ground motion data and concepts in seismic hazard analysis

The strong motion data from the Izmit, Turkey and Chi-Chi, Taiwan earthquakes have pointed out uncertainties in current strong motion attenuation curves for large earthquakes. Although the near-source strong motion data from these two well-recorded large earthquakes were well below the estimated values by the ground motion models, they were consistent with constraints estimated from precarious rock methodology. This discrepancy could be a result of inadequate ground motion data for large earthquakes and possible flaws with a number of statistical parameter assumptions that were necessary for extrapolation from existing database, which is dominated by small earthquake data. This review article discusses several important issues that have the potential to cause major impact on seismic hazard analysis. They are: (i) partitioning of uncertainties into aleatory and epistemic contributions, (ii) quantification of precarious rock observations and use of the data to constrain and improve ground motion models, (iii) continuing to deploy strong motion instruments near major faults since only more strong motion data will definitively resolve the issues of what is normal behaviour, and (iv) understanding through modelling and observations, the physical phenomena that affect strong motion, including the effect of total fault offset, surface rupture and type of faulting.