Metrics for Assessing Earthquake‐Hazard Map Performance

Abstract

Recent large earthquakes that caused great damage in areas predicted to be relatively safe, illustrate the importance of criteria that assess how well earthquake hazard maps used to develop codes for earthquake-resistant construction are actually performing. At present, there is no agreed-upon way of assessing how well a map performed and thus determining whether one map performed better than another. The fractional site exceedance metric implicit in current maps, that during the chosen time interval the predicted ground motion will be exceeded only at a specific fraction of the sites, is useful but permits maps to be nominally successful even if they significantly underpredict or overpredict shaking, or permits them to be nominally unsuccessful but do well in terms of predicting shaking. We explore some possible metrics that better measure the effects of overprediction and underprediction and can be weighted to reflect the two differently and to reflect differences in populations and property at risk. Although no single metric alone fully characterizes map behavior, using several metrics can provide useful insight for comparing and improving hazard maps. For example, both probabilistic and deterministic hazard maps for Italy dramatically overpredict the recorded shaking in a 2200-yr-long historical intensity catalog, illustrating problems in the data (most likely), models, or both.

Tsunamis: bridging science, engineering and society

“…Hence, Stein et al [119] assert that it is better to recognize and communicate the uncertainties involved. They thus propose methods to assess how well a specific map performed and how to revise maps [120].…”

Challenges in assessing seismic hazard in intraplate Europe

“…Similar approaches are used to present uncertainties for analogous forecasts with significant economic and policy implications (Stein et al 2015a).…”

“…3. Assumed probability p that during a t-year-long observation period, shaking at a site will exceed a value that is expected on average once in a T-year return period (Stein et al 2015a). Reproduced with permission of the Seismological Society of America.…”

“…4. Comparison of (a) historical intensity data for Italy with (b) probabilistic and (c) deterministic hazard maps, both of which over-predict the observed shaking (Stein et al 2015a). Reproduced with permission of the Seismological Society of America.…”

“…Comparison of successive Italian hazard maps(Stein et al 2015a), which forecast some earthquake locations well and others poorly. The 1999 map was updated to reflect the 2002 Molise earthquake and the 2006 map will probably be updated after the 2012 Emilia earthquake.…”