Blenheim Paleoliquefaction Trenching Many Proximal Fault Sources and
Blenheim Paleo-liquefaction Trenching
Many Proximal Fault Sources and Susceptible Sediments • Liquefaction previously reported in area following large earthquakes • 2013 Mw 6. 6 Lake Grassmere • 1885 Mw ~8. 2 Wairarapa • 1848 Mw ~7. 5 Marlborough
Trenching at sites where liquefaction was and was not observed in 2016 yet was predicted
Vernon Street • Liquefaction predicted for 2016 but not observed • No subsurface liquefaction features observed • Excavated to 3. 3 m depth • Stratigraphy comprised predominantly cohesive silts to 2. 7 m depth with thin (10 cm thick) silty fine sand lenses • Below 2. 7 m depth is fine to medium sand with shells
Equestrian Park • Liquefaction and lateral spreading observed following the 2016 earthquake • Excavation to approx. 4+ m depth • Predominantly silts (cohesive) to 4 m depth with thin (10 cm thick) silty fine to very fine sand lenses • Blue grey sand encountered below ~4 m – trench collapse
Lansdowne Park • Liquefaction observed following the 2016 Kaikoura earthquake • No liquefaction features observed in trench albeit recorded at the site • Trench excavated to 2. 5 m depth • Predominantly silt to 2. 3 m depth • Thin sand lens present from 2. 3 – 2. 45 m depth • 2. 5 m depth transition to medium to coarse sand with floating gravel clasts and wood (log) Trench
Blenheim Rowing Club • Liquefaction observed in paleochannel of Wairau River • Excavation in paleo-channel • Silt with thin sand lenses to 2. 5 m depth – interlayered at 30 -40 cm thick scale • Transition to blue-grey at 1. 7 m • Excavation in paleo-flood plain • 0 -3 m depth = plastic silt with no distinct sand layers • Transition to blue-grey at 3. 2 m depth • 4. 5 m depth excavation ceased due to trench collapse – still cohesive silts • 4. 2 m depth dike present in silt
Initial observations • A lot of silt present in trenches • Comparably thin sand lenses present in top 2 -3 m • All liquefaction sites located near waterways indicating influences of lateral spreading
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