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Volume 17, issue 5 | Copyright
Nat. Hazards Earth Syst. Sci., 17, 781-800, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 01 Jun 2017

Research article | 01 Jun 2017

Evaluating simplified methods for liquefaction assessment for loss estimation

Indranil Kongar1, Tiziana Rossetto1, and Sonia Giovinazzi2 Indranil Kongar et al.
  • 1Earthquake and People Interaction Centre (EPICentre), Department of Civil, Environmental and Geomatic Engineering, University College London, London, WC1E 6BT, UK
  • 2Department of Civil and Natural Resources Engineering, University of Canterbury, Christchurch, 8140, New Zealand

Abstract. Currently, some catastrophe models used by the insurance industry account for liquefaction by applying a simple factor to shaking-induced losses. The factor is based only on local liquefaction susceptibility and this highlights the need for a more sophisticated approach to incorporating the effects of liquefaction in loss models. This study compares 11 unique models, each based on one of three principal simplified liquefaction assessment methods: liquefaction potential index (LPI) calculated from shear-wave velocity, the HAZUS software method and a method created specifically to make use of USGS remote sensing data. Data from the September 2010 Darfield and February 2011 Christchurch earthquakes in New Zealand are used to compare observed liquefaction occurrences to forecasts from these models using binary classification performance measures. The analysis shows that the best-performing model is the LPI calculated using known shear-wave velocity profiles, which correctly forecasts 78% of sites where liquefaction occurred and 80% of sites where liquefaction did not occur, when the threshold is set at 7. However, these data may not always be available to insurers. The next best model is also based on LPI but uses shear-wave velocity profiles simulated from the combination of USGS VS30 data and empirical functions that relate VS30 to average shear-wave velocities at shallower depths. This model correctly forecasts 58% of sites where liquefaction occurred and 84% of sites where liquefaction did not occur, when the threshold is set at 4. These scores increase to 78 and 86%, respectively, when forecasts are based on liquefaction probabilities that are empirically related to the same values of LPI. This model is potentially more useful for insurance since the input data are publicly available. HAZUS models, which are commonly used in studies where no local model is available, perform poorly and incorrectly forecast 87% of sites where liquefaction occurred, even at optimal thresholds. This paper also considers two models (HAZUS and EPOLLS) for estimation of the scale of liquefaction in terms of permanent ground deformation but finds that both models perform poorly, with correlations between observations and forecasts lower than 0.4 in all cases. Therefore these models potentially provide negligible additional value to loss estimation analysis outside of the regions for which they have been developed.

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Short summary
The purpose of this research is to evaluate the predictive capability of simplified liquefaction models that can be applied across wide geographical areas for insurance and risk management purposes. Predictions from nine models are compared to observations from the Canterbury earthquake sequence and finds that models based on a previously proposed Liquefaction Potential Index perform the best, whilst the commonly used HAZUS methodology does not perform well.
The purpose of this research is to evaluate the predictive capability of simplified liquefaction...