Liquefaction Hazard Mapping Liquefaction Vulnerability Mapping for a

Liquefaction Hazard Mapping Liquefaction Vulnerability Mapping for a Given Return Period versus Return Period Mapping for a Given Severity of Liquefaction Vulnerability V. Lacrosse, S. van Ballegooy, M. Ogden

Overview • Common practice • Liquefaction assessment parameters • New methodology • Liquefaction Vulnerability Mapping • Present the median or mean liquefaction vulnerability for a given level of earthquake shaking • Liquefaction Return Period Mapping • Determine the level of earthquake shaking required to attain a given level of liquefaction vulnerability • Future work

Common Practice

Liquefaction Assessment Parameters Liquefaction Triggering Method Boulanger & Idriss (2014) Liquefaction Calculated Deformation Method Zhang et al. (2002) Liquefaction Vulnerability Parameter Liquefaction Severity Number Probability of Liquefaction (CRR Curve) PL = 50% Geotechnical Investigations CPT (from NZGD) Magnitude 6

New Methodology

Similar Expected Ground Performance Areas GY O HOL P R MO O E G ELEV ATIO DEPTH TO GROUNDW ATE R FACE SUB-SUR Y GEOLOG N

LSN Liquefaction Vulnerability Functions PGA (g)

Liquefaction Vulnerability Functions

Frequency Density Liquefaction Vulnerability Functions LSN

Liquefaction Vulnerability Mapping

LSN Liquefaction Return Period Mapping PGA (g)

Liquefaction Return Period Mapping

Liquefaction Return Period Mapping ~25 -200 yr ~25 -100 yr >1000 yr ~50 -500 yr ~25 -100 yr ~500 -1000 yr

Future Work • Main focus – spatial variability • Despite spatial variability in ground conditions, land generally performs homogeneously • Case history in areas of similar expected performance • Over-prediction in spatial variability? • Should standard deviation be reduced? • Develop methodology in areas with less data • Create a potential liquefaction hazard map for all of New Zealand

Conclusions • Methodology is applicable regardless of number of investigations • Emphasis on consideration of geomorphology, geology, elevation, groundwater depth • By creating areas of similar expected ground performance, can account for spatial variability and uncertainty • There are different ways of presenting liquefaction vulnerability • Liquefaction return period map more aligned with other hazards

Acknowledgements Co-authors Sjoerd van Ballegooy (T+T) Matt Ogden (T+T)